Merging upstream version 127.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

265 files changed, 8283 insertions, 0 deletions

diff --git a/third_party/rust/zerocopy/tests/trybuild.rs b/third_party/rust/zerocopy/tests/trybuild.rs
new file mode 100644
index 0000000000..24abc28622
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/trybuild.rs
@@ -0,0 +1,41 @@
+// Copyright 2019 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+use testutil::ToolchainVersion;
+
+#[test]
+#[cfg_attr(miri, ignore)]
+fn ui() {
+    let version = ToolchainVersion::extract_from_pwd().unwrap();
+    // See the doc comment on this method for an explanation of what this does
+    // and why we store source files in different directories.
+    let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
+
+    let t = trybuild::TestCases::new();
+    t.compile_fail(format!("tests/{source_files_dirname}/*.rs"));
+}
+
+// The file `invalid-impls.rs` directly includes `src/macros.rs` in order to
+// test the `impl_or_verify!` macro which is defined in that file. Specifically,
+// it tests the verification portion of that macro, which is enabled when
+// `cfg(any(feature = "derive", test))`. While `--cfg test` is of course passed
+// to the code in the file you're reading right now, `trybuild` does not pass
+// `--cfg test` when it invokes Cargo. As a result, this `trybuild` test only
+// tests the correct behavior when the "derive" feature is enabled.
+#[cfg(feature = "derive")]
+#[test]
+#[cfg_attr(miri, ignore)]
+fn ui_invalid_impls() {
+    let version = ToolchainVersion::extract_from_pwd().unwrap();
+    // See the doc comment on this method for an explanation of what this does
+    // and why we store source files in different directories.
+    let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
+
+    let t = trybuild::TestCases::new();
+    t.compile_fail(format!("tests/{source_files_dirname}/invalid-impls/*.rs"));
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.rs
new file mode 100644
index 0000000000..45b6138f47
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.rs
@@ -0,0 +1,12 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because `UnsafeCell<u32>: !FromBytes`.
+const NOT_FROM_BYTES: core::cell::UnsafeCell<u32> =
+    include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.stderr
new file mode 100644
index 0000000000..21f6443bbf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/include_value_not_from_bytes.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `UnsafeCell<u32>: FromBytes` is not satisfied
+  --> tests/ui-msrv/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `UnsafeCell<u32>`
+   |
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-msrv/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `$crate::transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.rs b/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.rs
new file mode 100644
index 0000000000..d87b30698b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.rs
@@ -0,0 +1,11 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because the file is 4 bytes long, not 8.
+const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.stderr b/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.stderr
new file mode 100644
index 0000000000..30045849d7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/include_value_wrong_size.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/include_value_wrong_size.rs:11:25
+   |
+11 | const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 4]` (32 bits)
+   = note: target type: `u64` (64 bits)
+   = note: this error originates in the macro `$crate::transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.rs b/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.rs
new file mode 100644
index 0000000000..ea963907df
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.rs
@@ -0,0 +1,29 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// Since some macros from `macros.rs` are unused.
+#![allow(unused)]
+
+extern crate zerocopy;
+extern crate zerocopy_derive;
+
+include!("../../../src/macros.rs");
+
+use zerocopy::*;
+use zerocopy_derive::*;
+
+fn main() {}
+
+#[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+#[repr(transparent)]
+struct Foo<T>(T);
+
+impl_or_verify!(T => FromZeroes for Foo<T>);
+impl_or_verify!(T => FromBytes for Foo<T>);
+impl_or_verify!(T => AsBytes for Foo<T>);
+impl_or_verify!(T => Unaligned for Foo<T>);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.stderr b/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.stderr
new file mode 100644
index 0000000000..c1de466ece
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/invalid-impls/invalid-impls.stderr
@@ -0,0 +1,127 @@
+error[E0277]: the trait bound `T: zerocopy::FromZeroes` is not satisfied
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             impl<$($tyvar $(: $(? $optbound +)* $($bound +)*)?),*> Subtrait for $ty {}
+   |                                                                    ^^^^^^^^ the trait `zerocopy::FromZeroes` is not implemented for `T`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:26:1
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   | ------------------------------------------- in this macro invocation
+   |
+note: required because of the requirements on the impl of `zerocopy::FromZeroes` for `Foo<T>`
+  --> tests/ui-msrv/invalid-impls/invalid-impls.rs:22:10
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |          ^^^^^^^^^^
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `_::Subtrait`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:26:1
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   | ------------------------------------------- in this macro invocation
+   = note: this error originates in the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+26 | impl_or_verify!(T: zerocopy::FromZeroes => FromZeroes for Foo<T>);
+   |                  ++++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::FromBytes` is not satisfied
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             impl<$($tyvar $(: $(? $optbound +)* $($bound +)*)?),*> Subtrait for $ty {}
+   |                                                                    ^^^^^^^^ the trait `zerocopy::FromBytes` is not implemented for `T`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:27:1
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   |
+note: required because of the requirements on the impl of `zerocopy::FromBytes` for `Foo<T>`
+  --> tests/ui-msrv/invalid-impls/invalid-impls.rs:22:22
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                      ^^^^^^^^^
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `_::Subtrait`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:27:1
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+27 | impl_or_verify!(T: zerocopy::FromBytes => FromBytes for Foo<T>);
+   |                  +++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::AsBytes` is not satisfied
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             impl<$($tyvar $(: $(? $optbound +)* $($bound +)*)?),*> Subtrait for $ty {}
+   |                                                                    ^^^^^^^^ the trait `zerocopy::AsBytes` is not implemented for `T`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:28:1
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   | ---------------------------------------- in this macro invocation
+   |
+note: required because of the requirements on the impl of `zerocopy::AsBytes` for `Foo<T>`
+  --> tests/ui-msrv/invalid-impls/invalid-impls.rs:22:33
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                 ^^^^^^^
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `_::Subtrait`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:28:1
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   | ---------------------------------------- in this macro invocation
+   = note: this error originates in the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+28 | impl_or_verify!(T: zerocopy::AsBytes => AsBytes for Foo<T>);
+   |                  +++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::Unaligned` is not satisfied
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             impl<$($tyvar $(: $(? $optbound +)* $($bound +)*)?),*> Subtrait for $ty {}
+   |                                                                    ^^^^^^^^ the trait `zerocopy::Unaligned` is not implemented for `T`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:29:1
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   |
+note: required because of the requirements on the impl of `zerocopy::Unaligned` for `Foo<T>`
+  --> tests/ui-msrv/invalid-impls/invalid-impls.rs:22:42
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                          ^^^^^^^^^
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-msrv/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `_::Subtrait`
+   |
+  ::: tests/ui-msrv/invalid-impls/invalid-impls.rs:29:1
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+29 | impl_or_verify!(T: zerocopy::Unaligned => Unaligned for Foo<T>);
+   |                  +++++++++++++++++++++
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/max-align.rs b/third_party/rust/zerocopy/tests/ui-msrv/max-align.rs
new file mode 100644
index 0000000000..53e3eb9b0a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/max-align.rs
@@ -0,0 +1,99 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+#[repr(C, align(1))]
+struct Align1;
+
+#[repr(C, align(2))]
+struct Align2;
+
+#[repr(C, align(4))]
+struct Align4;
+
+#[repr(C, align(8))]
+struct Align8;
+
+#[repr(C, align(16))]
+struct Align16;
+
+#[repr(C, align(32))]
+struct Align32;
+
+#[repr(C, align(64))]
+struct Align64;
+
+#[repr(C, align(128))]
+struct Align128;
+
+#[repr(C, align(256))]
+struct Align256;
+
+#[repr(C, align(512))]
+struct Align512;
+
+#[repr(C, align(1024))]
+struct Align1024;
+
+#[repr(C, align(2048))]
+struct Align2048;
+
+#[repr(C, align(4096))]
+struct Align4096;
+
+#[repr(C, align(8192))]
+struct Align8192;
+
+#[repr(C, align(16384))]
+struct Align16384;
+
+#[repr(C, align(32768))]
+struct Align32768;
+
+#[repr(C, align(65536))]
+struct Align65536;
+
+#[repr(C, align(131072))]
+struct Align131072;
+
+#[repr(C, align(262144))]
+struct Align262144;
+
+#[repr(C, align(524288))]
+struct Align524288;
+
+#[repr(C, align(1048576))]
+struct Align1048576;
+
+#[repr(C, align(2097152))]
+struct Align2097152;
+
+#[repr(C, align(4194304))]
+struct Align4194304;
+
+#[repr(C, align(8388608))]
+struct Align8388608;
+
+#[repr(C, align(16777216))]
+struct Align16777216;
+
+#[repr(C, align(33554432))]
+struct Align33554432;
+
+#[repr(C, align(67108864))]
+struct Align67108864;
+
+#[repr(C, align(134217728))]
+struct Align13421772;
+
+#[repr(C, align(268435456))]
+struct Align26843545;
+
+#[repr(C, align(1073741824))]
+struct Align1073741824;
+
+fn main() {}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/max-align.stderr b/third_party/rust/zerocopy/tests/ui-msrv/max-align.stderr
new file mode 100644
index 0000000000..6ab6e47e2b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/max-align.stderr
@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-msrv/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.rs
new file mode 100644
index 0000000000..c4caaff917
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..b4afbbd60c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-dst-not-frombytes.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-msrv/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `NotZerocopy`
+   |
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-msrv/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.rs
new file mode 100644
index 0000000000..0928564dd5
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.stderr
new file mode 100644
index 0000000000..033031c91b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-alignment-increase.stderr
@@ -0,0 +1,36 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-alignment-increase.rs:19:39
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-msrv/transmute-mut-alignment-increase.rs:19:54
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                                      ^^^^^^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+
+error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], AU16>` in constants
+  --> tests/ui-msrv/transmute-mut-alignment-increase.rs:19:39
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-msrv/transmute-mut-alignment-increase.rs:19:59
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                       --------------------^^^^^^^^-
+   |                                       |                   |
+   |                                       |                   creates a temporary which is freed while still in use
+   |                                       temporary value is freed at the end of this statement
+   |                                       using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.rs
new file mode 100644
index 0000000000..021b562f18
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.rs
@@ -0,0 +1,20 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+
+// `transmute_mut!` cannot, generally speaking, be used in const contexts.
+const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.stderr
new file mode 100644
index 0000000000..30bfe45412
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-const.stderr
@@ -0,0 +1,41 @@
+warning: taking a mutable reference to a `const` item
+  --> tests/ui-msrv/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(const_item_mutation)]` on by default
+   = note: each usage of a `const` item creates a new temporary
+   = note: the mutable reference will refer to this temporary, not the original `const` item
+note: `const` item defined here
+  --> tests/ui-msrv/transmute-mut-const.rs:17:1
+   |
+17 | const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-msrv/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+
+error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], [u8; 2]>` in constants
+  --> tests/ui-msrv/transmute-mut-const.rs:20:37
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-msrv/transmute-mut-const.rs:20:57
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     --------------------^^^^^^^^^^^^-
+   |                                     |                   |
+   |                                     |                   creates a temporary which is freed while still in use
+   |                                     temporary value is freed at the end of this statement
+   |                                     using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.rs
new file mode 100644
index 0000000000..7068f1026d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(u: &mut u8) -> &mut T {
+    // `transmute_mut!` requires the destination type to be concrete.
+    transmute_mut!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.stderr
new file mode 100644
index 0000000000..f6b54ce1c2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.rs
new file mode 100644
index 0000000000..33a9ecd955
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..8f0ea801ef
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-a-reference.stderr
@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.rs
new file mode 100644
index 0000000000..b72f12928c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `AsBytes`
+const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.stderr
new file mode 100644
index 0000000000..7e2dd78b8f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-asbytes.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `Dst: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Dst`
+   |
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.rs
new file mode 100644
index 0000000000..102fcedc9a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..663e085a30
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-not-frombytes.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `Dst: FromBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Dst`
+   |
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.rs
new file mode 100644
index 0000000000..693ccda56f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.stderr
new file mode 100644
index 0000000000..cb60a82a78
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-dst-unsized.stderr
@@ -0,0 +1,108 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                         ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                          ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.rs
new file mode 100644
index 0000000000..c31765e4b9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let mut x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.stderr
new file mode 100644
index 0000000000..5ff7145966
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-illegal-lifetime.stderr
@@ -0,0 +1,9 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-msrv/transmute-mut-illegal-lifetime.rs:14:56
+   |
+14 |     let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+   |            ----------------                            ^^^^^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.rs
new file mode 100644
index 0000000000..c6eec3a9c2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// We require that the size of the destination type is not smaller than the size
+// of the source type.
+const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.stderr
new file mode 100644
index 0000000000..2bfc21898b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-decrease.stderr
@@ -0,0 +1,36 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-size-decrease.rs:17:32
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-msrv/transmute-mut-size-decrease.rs:17:47
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                               ^^^^^^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+
+error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], u8>` in constants
+  --> tests/ui-msrv/transmute-mut-size-decrease.rs:17:32
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-msrv/transmute-mut-size-decrease.rs:17:52
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                --------------------^^^^^^^^-
+   |                                |                   |
+   |                                |                   creates a temporary which is freed while still in use
+   |                                temporary value is freed at the end of this statement
+   |                                using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.rs
new file mode 100644
index 0000000000..a4657c2838
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.stderr
new file mode 100644
index 0000000000..6e866a0d32
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-size-increase.stderr
@@ -0,0 +1,36 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-size-increase.rs:17:37
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-msrv/transmute-mut-size-increase.rs:17:52
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                                    ^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+
+error[E0015]: cannot call non-const fn `transmute_mut::<u8, [u8; 2]>` in constants
+  --> tests/ui-msrv/transmute-mut-size-increase.rs:17:37
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-msrv/transmute-mut-size-increase.rs:17:57
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                     --------------------^^^-
+   |                                     |                   |
+   |                                     |                   creates a temporary which is freed while still in use
+   |                                     temporary value is freed at the end of this statement
+   |                                     using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.rs
new file mode 100644
index 0000000000..aed7ded96f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes, U: AsBytes + FromBytes>(t: &mut T) -> &mut U {
+    // `transmute_mut!` requires the source and destination types to be
+    // concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.stderr
new file mode 100644
index 0000000000..1162f21f9c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.rs
new file mode 100644
index 0000000000..98cc520889
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.stderr
new file mode 100644
index 0000000000..c500a93af7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-not-references.stderr
@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-src-dst-not-references.rs:17:59
+   |
+17 | const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
+   |                                            ---------------^^^^^^-
+   |                                            |              |
+   |                                            |              expected `&mut _`, found `usize`
+   |                                            |              help: consider mutably borrowing here: `&mut 0usize`
+   |                                            expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.rs
new file mode 100644
index 0000000000..1bebcf2d68
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.stderr
new file mode 100644
index 0000000000..00201a6b68
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-dst-unsized.stderr
@@ -0,0 +1,237 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                      ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.rs
new file mode 100644
index 0000000000..a3ef397876
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+    // `transmute_mut!` requires the source type to be concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.stderr
new file mode 100644
index 0000000000..8a9296ca66
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-generic.stderr
@@ -0,0 +1,10 @@
+error[E0405]: cannot find trait `FromBytes` in this scope
+  --> tests/ui-msrv/transmute-mut-src-generic.rs:15:31
+   |
+15 | fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+   |                               ^^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+11 | use zerocopy::FromBytes;
+   |
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.rs
new file mode 100644
index 0000000000..08088d0db6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+fn ref_src_immutable() {
+    // `transmute_mut!` requires that its source type be a mutable reference.
+    let _: &mut u8 = transmute_mut!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.stderr
new file mode 100644
index 0000000000..8262f169a2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-immutable.stderr
@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-src-immutable.rs:17:37
+   |
+17 |     let _: &mut u8 = transmute_mut!(&0u8);
+   |                      ---------------^^^^-
+   |                      |              |
+   |                      |              types differ in mutability
+   |                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                      found reference `&u8`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.rs
new file mode 100644
index 0000000000..bf8bc32592
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.stderr
new file mode 100644
index 0000000000..3a6bdf78a6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-a-reference.stderr
@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-mut-src-not-a-reference.rs:17:53
+   |
+17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
+   |                                      ---------------^^^^^^-
+   |                                      |              |
+   |                                      |              expected `&mut _`, found `usize`
+   |                                      |              help: consider mutably borrowing here: `&mut 0usize`
+   |                                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.rs
new file mode 100644
index 0000000000..6a14f12fd0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.stderr
new file mode 100644
index 0000000000..4056975829
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-asbytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Src`
+   |
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Src`
+   |
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.rs
new file mode 100644
index 0000000000..2ebe03601b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `FromBytes`
+const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.stderr
new file mode 100644
index 0000000000..b859c41cd2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Src`
+   |
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-msrv/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Src`
+   |
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.rs
new file mode 100644
index 0000000000..413dd68d89
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.stderr
new file mode 100644
index 0000000000..6b18695e66
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-mut-src-unsized.stderr
@@ -0,0 +1,198 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                      ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.rs
new file mode 100644
index 0000000000..5af8859332
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.rs
@@ -0,0 +1,20 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// It is unclear whether we can or should support this transmutation, especially
+// in a const context. This test ensures that even if such a transmutation
+// becomes valid due to the requisite implementations of `FromBytes` being
+// added, that we re-examine whether it should specifically be valid in a const
+// context.
+const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.stderr
new file mode 100644
index 0000000000..06b1bbaf2d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ptr-to-usize.stderr
@@ -0,0 +1,37 @@
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
+   |
+   = help: the following implementations were found:
+             <usize as AsBytes>
+             <f32 as AsBytes>
+             <f64 as AsBytes>
+             <i128 as AsBytes>
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
+   |
+   = help: the following implementations were found:
+             <usize as AsBytes>
+             <f32 as AsBytes>
+             <f64 as AsBytes>
+             <i128 as AsBytes>
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.rs
new file mode 100644
index 0000000000..bf1988c66b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.stderr
new file mode 100644
index 0000000000..72864e144d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-alignment-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-alignment-increase.rs:19:35
+   |
+19 | const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.rs
new file mode 100644
index 0000000000..bf4a0f9adf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: FromBytes>(u: &u8) -> &T {
+    // `transmute_ref!` requires the destination type to be concrete.
+    transmute_ref!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.stderr
new file mode 100644
index 0000000000..ec7ec74894
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.rs
new file mode 100644
index 0000000000..fa0e6e4c9b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+fn ref_dst_mutable() {
+    // `transmute_ref!` requires that its destination type be an immutable
+    // reference.
+    let _: &mut u8 = transmute_ref!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.stderr
new file mode 100644
index 0000000000..5ccf2cd20d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-mutable.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.rs
new file mode 100644
index 0000000000..de55f9acdf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..9a61c4c7ce
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-a-reference.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.rs
new file mode 100644
index 0000000000..d81f64d21b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..d317675446
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-not-frombytes.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-msrv/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `NotZerocopy`
+   |
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-msrv/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.rs
new file mode 100644
index 0000000000..625f1fac07
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.stderr
new file mode 100644
index 0000000000..78135de876
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-dst-unsized.stderr
@@ -0,0 +1,94 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                         ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                                ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.rs
new file mode 100644
index 0000000000..8dd191e6f4
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static u64 = zerocopy::transmute_ref!(&x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.stderr
new file mode 100644
index 0000000000..866ea56a66
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-illegal-lifetime.stderr
@@ -0,0 +1,9 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-msrv/transmute-ref-illegal-lifetime.rs:14:52
+   |
+14 |     let _: &'static u64 = zerocopy::transmute_ref!(&x);
+   |            ------------                            ^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.rs
new file mode 100644
index 0000000000..1d66a54ef7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.stderr
new file mode 100644
index 0000000000..95669f9063
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-size-decrease.rs:17:28
+   |
+17 | const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.rs
new file mode 100644
index 0000000000..cdca560b30
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.stderr
new file mode 100644
index 0000000000..10f0e1038c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-size-increase.rs:17:33
+   |
+17 | const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
+   |                                 ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.rs
new file mode 100644
index 0000000000..409d785b20
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes, U: FromBytes>(t: &T) -> &U {
+    // `transmute_ref!` requires the source and destination types to be
+    // concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.stderr
new file mode 100644
index 0000000000..eb3268fa8f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.rs
new file mode 100644
index 0000000000..114e917b54
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.stderr
new file mode 100644
index 0000000000..2c5e23b6dd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-not-references.stderr
@@ -0,0 +1,42 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-src-dst-not-references.rs:17:54
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ---------------^^^^^^-
+   |                                       |              |
+   |                                       |              expected reference, found `usize`
+   |                                       |              help: consider borrowing here: `&0usize`
+   |                                       expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found reference
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.rs
new file mode 100644
index 0000000000..6bfe7ffdfd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.stderr
new file mode 100644
index 0000000000..adfd59792a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-dst-unsized.stderr
@@ -0,0 +1,195 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                      ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.rs
new file mode 100644
index 0000000000..010281c32e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes>(t: &T) -> &u8 {
+    // `transmute_ref!` requires the source type to be concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.stderr
new file mode 100644
index 0000000000..4cb3e51bc7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, u8>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.rs
new file mode 100644
index 0000000000..90661b3e2c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.stderr
new file mode 100644
index 0000000000..0f4aeec9e2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-a-reference.stderr
@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> tests/ui-msrv/transmute-ref-src-not-a-reference.rs:17:49
+   |
+17 | const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
+   |                                  ---------------^^^^^^-
+   |                                  |              |
+   |                                  |              expected reference, found `usize`
+   |                                  |              help: consider borrowing here: `&0usize`
+   |                                  expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.rs
new file mode 100644
index 0000000000..6ab19f3c82
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.stderr
new file mode 100644
index 0000000000..6b80d4f494
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-not-asbytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.rs
new file mode 100644
index 0000000000..14e72b4ddc
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.stderr
new file mode 100644
index 0000000000..43bac53595
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-ref-src-unsized.stderr
@@ -0,0 +1,170 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<T, U>(e: T) -> U;
+   |                      ^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-msrv/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all function arguments must have a statically known size
+   = note: this error originates in the macro `$crate::assert_size_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.rs
new file mode 100644
index 0000000000..1d56831f22
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: u8 = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.stderr
new file mode 100644
index 0000000000..ffa5688485
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-size-decrease.rs:19:27
+   |
+19 | const DECREASE_SIZE: u8 = transmute!(AU16(0));
+   |                           ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AU16` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.rs
new file mode 100644
index 0000000000..32f9363089
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: AU16 = transmute!(0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.stderr
new file mode 100644
index 0000000000..865d0caf9e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-msrv/transmute-size-increase.rs:19:29
+   |
+19 | const INCREASE_SIZE: AU16 = transmute!(0u8);
+   |                             ^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `AU16` (16 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.rs
new file mode 100644
index 0000000000..dd730216b6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.stderr
new file mode 100644
index 0000000000..93eeda0c26
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-msrv/transmute-src-not-asbytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-msrv/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-msrv/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.rs
new file mode 100644
index 0000000000..45b6138f47
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.rs
@@ -0,0 +1,12 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because `UnsafeCell<u32>: !FromBytes`.
+const NOT_FROM_BYTES: core::cell::UnsafeCell<u32> =
+    include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.stderr
new file mode 100644
index 0000000000..d948a0db81
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/include_value_not_from_bytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `UnsafeCell<u32>: FromBytes` is not satisfied
+  --> tests/ui-nightly/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     the trait `FromBytes` is not implemented for `UnsafeCell<u32>`
+   |     required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-nightly/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `$crate::transmute` which comes from the expansion of the macro `include_value` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.rs b/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.rs
new file mode 100644
index 0000000000..d87b30698b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.rs
@@ -0,0 +1,11 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because the file is 4 bytes long, not 8.
+const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.stderr b/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.stderr
new file mode 100644
index 0000000000..f592ece1de
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/include_value_wrong_size.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/include_value_wrong_size.rs:11:25
+   |
+11 | const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 4]` (32 bits)
+   = note: target type: `u64` (64 bits)
+   = note: this error originates in the macro `$crate::transmute` which comes from the expansion of the macro `include_value` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.rs b/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.rs
new file mode 100644
index 0000000000..ea963907df
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.rs
@@ -0,0 +1,29 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// Since some macros from `macros.rs` are unused.
+#![allow(unused)]
+
+extern crate zerocopy;
+extern crate zerocopy_derive;
+
+include!("../../../src/macros.rs");
+
+use zerocopy::*;
+use zerocopy_derive::*;
+
+fn main() {}
+
+#[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+#[repr(transparent)]
+struct Foo<T>(T);
+
+impl_or_verify!(T => FromZeroes for Foo<T>);
+impl_or_verify!(T => FromBytes for Foo<T>);
+impl_or_verify!(T => AsBytes for Foo<T>);
+impl_or_verify!(T => Unaligned for Foo<T>);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.stderr b/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.stderr
new file mode 100644
index 0000000000..e5651d169e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/invalid-impls/invalid-impls.stderr
@@ -0,0 +1,107 @@
+error[E0277]: the trait bound `T: zerocopy::FromZeroes` is not satisfied
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:26:37
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   |                                     ^^^^^^ the trait `zerocopy::FromZeroes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::FromZeroes`
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:22:10
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |          ^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-nightly/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-nightly/invalid-impls/invalid-impls.rs:26:1
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   | ------------------------------------------- in this macro invocation
+   = note: this error originates in the derive macro `FromZeroes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+26 | impl_or_verify!(T: zerocopy::FromZeroes => FromZeroes for Foo<T>);
+   |                  ++++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::FromBytes` is not satisfied
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:27:36
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   |                                    ^^^^^^ the trait `zerocopy::FromBytes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::FromBytes`
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:22:22
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                      ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-nightly/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-nightly/invalid-impls/invalid-impls.rs:27:1
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the derive macro `FromBytes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+27 | impl_or_verify!(T: zerocopy::FromBytes => FromBytes for Foo<T>);
+   |                  +++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::AsBytes` is not satisfied
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:28:34
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   |                                  ^^^^^^ the trait `zerocopy::AsBytes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::AsBytes`
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:22:33
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                 ^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-nightly/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-nightly/invalid-impls/invalid-impls.rs:28:1
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   | ---------------------------------------- in this macro invocation
+   = note: this error originates in the derive macro `AsBytes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+28 | impl_or_verify!(T: zerocopy::AsBytes => AsBytes for Foo<T>);
+   |                  +++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::Unaligned` is not satisfied
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:29:36
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   |                                    ^^^^^^ the trait `zerocopy::Unaligned` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::Unaligned`
+  --> tests/ui-nightly/invalid-impls/invalid-impls.rs:22:42
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                          ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-nightly/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-nightly/invalid-impls/invalid-impls.rs:29:1
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the derive macro `Unaligned` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+29 | impl_or_verify!(T: zerocopy::Unaligned => Unaligned for Foo<T>);
+   |                  +++++++++++++++++++++
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/max-align.rs b/third_party/rust/zerocopy/tests/ui-nightly/max-align.rs
new file mode 100644
index 0000000000..53e3eb9b0a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/max-align.rs
@@ -0,0 +1,99 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+#[repr(C, align(1))]
+struct Align1;
+
+#[repr(C, align(2))]
+struct Align2;
+
+#[repr(C, align(4))]
+struct Align4;
+
+#[repr(C, align(8))]
+struct Align8;
+
+#[repr(C, align(16))]
+struct Align16;
+
+#[repr(C, align(32))]
+struct Align32;
+
+#[repr(C, align(64))]
+struct Align64;
+
+#[repr(C, align(128))]
+struct Align128;
+
+#[repr(C, align(256))]
+struct Align256;
+
+#[repr(C, align(512))]
+struct Align512;
+
+#[repr(C, align(1024))]
+struct Align1024;
+
+#[repr(C, align(2048))]
+struct Align2048;
+
+#[repr(C, align(4096))]
+struct Align4096;
+
+#[repr(C, align(8192))]
+struct Align8192;
+
+#[repr(C, align(16384))]
+struct Align16384;
+
+#[repr(C, align(32768))]
+struct Align32768;
+
+#[repr(C, align(65536))]
+struct Align65536;
+
+#[repr(C, align(131072))]
+struct Align131072;
+
+#[repr(C, align(262144))]
+struct Align262144;
+
+#[repr(C, align(524288))]
+struct Align524288;
+
+#[repr(C, align(1048576))]
+struct Align1048576;
+
+#[repr(C, align(2097152))]
+struct Align2097152;
+
+#[repr(C, align(4194304))]
+struct Align4194304;
+
+#[repr(C, align(8388608))]
+struct Align8388608;
+
+#[repr(C, align(16777216))]
+struct Align16777216;
+
+#[repr(C, align(33554432))]
+struct Align33554432;
+
+#[repr(C, align(67108864))]
+struct Align67108864;
+
+#[repr(C, align(134217728))]
+struct Align13421772;
+
+#[repr(C, align(268435456))]
+struct Align26843545;
+
+#[repr(C, align(1073741824))]
+struct Align1073741824;
+
+fn main() {}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/max-align.stderr b/third_party/rust/zerocopy/tests/ui-nightly/max-align.stderr
new file mode 100644
index 0000000000..0cadb9a99a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/max-align.stderr
@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-nightly/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.rs
new file mode 100644
index 0000000000..c4caaff917
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..a9f1f7becf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-nightly/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^
+   |                                         |
+   |                                         the trait `FromBytes` is not implemented for `NotZerocopy`
+   |                                         required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-nightly/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.rs
new file mode 100644
index 0000000000..0928564dd5
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.stderr
new file mode 100644
index 0000000000..0666f8b526
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-alignment-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-alignment-increase.rs:19:39
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.rs
new file mode 100644
index 0000000000..021b562f18
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.rs
@@ -0,0 +1,20 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+
+// `transmute_mut!` cannot, generally speaking, be used in const contexts.
+const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.stderr
new file mode 100644
index 0000000000..fa53ed09a9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-const.stderr
@@ -0,0 +1,42 @@
+warning: taking a mutable reference to a `const` item
+  --> tests/ui-nightly/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: each usage of a `const` item creates a new temporary
+   = note: the mutable reference will refer to this temporary, not the original `const` item
+note: `const` item defined here
+  --> tests/ui-nightly/transmute-mut-const.rs:17:1
+   |
+17 | const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(const_item_mutation)]` on by default
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-nightly/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+   = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
+
+error[E0015]: cannot call non-const fn `transmute_mut::<'_, '_, [u8; 2], [u8; 2]>` in constants
+  --> tests/ui-nightly/transmute-mut-const.rs:20:37
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-nightly/transmute-mut-const.rs:20:57
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     --------------------^^^^^^^^^^^^-
+   |                                     |                   |
+   |                                     |                   creates a temporary value which is freed while still in use
+   |                                     temporary value is freed at the end of this statement
+   |                                     using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.rs
new file mode 100644
index 0000000000..7068f1026d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(u: &mut u8) -> &mut T {
+    // `transmute_mut!` requires the destination type to be concrete.
+    transmute_mut!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.stderr
new file mode 100644
index 0000000000..f278558cf8
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.rs
new file mode 100644
index 0000000000..33a9ecd955
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..a84547bd03
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-a-reference.stderr
@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.rs
new file mode 100644
index 0000000000..b72f12928c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `AsBytes`
+const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.stderr
new file mode 100644
index 0000000000..54c8e6023f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-asbytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Dst: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    the trait `AsBytes` is not implemented for `Dst`
+   |                                    required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.rs
new file mode 100644
index 0000000000..102fcedc9a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..ea2123bc0b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Dst: FromBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                      |
+   |                                      the trait `FromBytes` is not implemented for `Dst`
+   |                                      required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.rs
new file mode 100644
index 0000000000..693ccda56f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.stderr
new file mode 100644
index 0000000000..a670e25013
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-dst-unsized.stderr
@@ -0,0 +1,86 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                          ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.rs
new file mode 100644
index 0000000000..c31765e4b9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let mut x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.stderr
new file mode 100644
index 0000000000..b826fcc7a9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-illegal-lifetime.stderr
@@ -0,0 +1,12 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-nightly/transmute-mut-illegal-lifetime.rs:14:56
+   |
+12 |     let mut x = 0u64;
+   |         ----- binding `x` declared here
+13 |     // It is illegal to increase the lifetime scope.
+14 |     let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+   |            ----------------                            ^^^^^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.rs
new file mode 100644
index 0000000000..c6eec3a9c2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// We require that the size of the destination type is not smaller than the size
+// of the source type.
+const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.stderr
new file mode 100644
index 0000000000..ac1e35cec7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-size-decrease.rs:17:32
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.rs
new file mode 100644
index 0000000000..a4657c2838
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.stderr
new file mode 100644
index 0000000000..d343bd65e6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-size-increase.rs:17:37
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.rs
new file mode 100644
index 0000000000..aed7ded96f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes, U: AsBytes + FromBytes>(t: &mut T) -> &mut U {
+    // `transmute_mut!` requires the source and destination types to be
+    // concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.stderr
new file mode 100644
index 0000000000..e3f3a3fd79
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.rs
new file mode 100644
index 0000000000..98cc520889
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.stderr
new file mode 100644
index 0000000000..df3cf2dba0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-not-references.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-src-dst-not-references.rs:17:59
+   |
+17 | const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
+   |                                            ---------------^^^^^^-
+   |                                            |              |
+   |                                            |              expected `&mut _`, found `usize`
+   |                                            expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
+help: consider mutably borrowing here
+   |
+17 | const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(&mut 0usize);
+   |                                                           ++++
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.rs
new file mode 100644
index 0000000000..1bebcf2d68
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.stderr
new file mode 100644
index 0000000000..0f41a420eb
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-dst-unsized.stderr
@@ -0,0 +1,231 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                          ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.rs
new file mode 100644
index 0000000000..a3ef397876
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+    // `transmute_mut!` requires the source type to be concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.stderr
new file mode 100644
index 0000000000..c06d775072
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-generic.stderr
@@ -0,0 +1,10 @@
+error[E0405]: cannot find trait `FromBytes` in this scope
+  --> tests/ui-nightly/transmute-mut-src-generic.rs:15:31
+   |
+15 | fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+   |                               ^^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+11 + use zerocopy::FromBytes;
+   |
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.rs
new file mode 100644
index 0000000000..08088d0db6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+fn ref_src_immutable() {
+    // `transmute_mut!` requires that its source type be a mutable reference.
+    let _: &mut u8 = transmute_mut!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.stderr
new file mode 100644
index 0000000000..7b7969d5d5
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-immutable.stderr
@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-src-immutable.rs:17:37
+   |
+17 |     let _: &mut u8 = transmute_mut!(&0u8);
+   |                      ---------------^^^^-
+   |                      |              |
+   |                      |              types differ in mutability
+   |                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                      found reference `&u8`
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.rs
new file mode 100644
index 0000000000..bf8bc32592
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.stderr
new file mode 100644
index 0000000000..12b7674f0e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-a-reference.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-mut-src-not-a-reference.rs:17:53
+   |
+17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
+   |                                      ---------------^^^^^^-
+   |                                      |              |
+   |                                      |              expected `&mut _`, found `usize`
+   |                                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
+help: consider mutably borrowing here
+   |
+17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(&mut 0usize);
+   |                                                     ++++
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.rs
new file mode 100644
index 0000000000..6a14f12fd0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.stderr
new file mode 100644
index 0000000000..b755d3c654
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    the trait `AsBytes` is not implemented for `Src`
+   |                                    required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Src`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.rs
new file mode 100644
index 0000000000..2ebe03601b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `FromBytes`
+const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.stderr
new file mode 100644
index 0000000000..5a9f0a7a7f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-not-frombytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                      |
+   |                                      the trait `FromBytes` is not implemented for `Src`
+   |                                      required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-nightly/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Src`
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.rs
new file mode 100644
index 0000000000..413dd68d89
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.stderr
new file mode 100644
index 0000000000..99475adee0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-mut-src-unsized.stderr
@@ -0,0 +1,158 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.rs
new file mode 100644
index 0000000000..5af8859332
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.rs
@@ -0,0 +1,20 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// It is unclear whether we can or should support this transmutation, especially
+// in a const context. This test ensures that even if such a transmutation
+// becomes valid due to the requisite implementations of `FromBytes` being
+// added, that we re-examine whether it should specifically be valid in a const
+// context.
+const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.stderr
new file mode 100644
index 0000000000..2fcba2fb6f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ptr-to-usize.stderr
@@ -0,0 +1,30 @@
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                              |
+   |                              the trait `AsBytes` is not implemented for `*const usize`
+   |                              required by a bound introduced by this call
+   |
+   = help: the trait `AsBytes` is implemented for `usize`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
+   |
+   = help: the trait `AsBytes` is implemented for `usize`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.rs
new file mode 100644
index 0000000000..bf1988c66b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.stderr
new file mode 100644
index 0000000000..1cef246bc3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-alignment-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-alignment-increase.rs:19:35
+   |
+19 | const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.rs
new file mode 100644
index 0000000000..bf4a0f9adf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: FromBytes>(u: &u8) -> &T {
+    // `transmute_ref!` requires the destination type to be concrete.
+    transmute_ref!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.stderr
new file mode 100644
index 0000000000..4c94d501c2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.rs
new file mode 100644
index 0000000000..fa0e6e4c9b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+fn ref_dst_mutable() {
+    // `transmute_ref!` requires that its destination type be an immutable
+    // reference.
+    let _: &mut u8 = transmute_ref!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.stderr
new file mode 100644
index 0000000000..0cbdd176b8
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-mutable.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.rs
new file mode 100644
index 0000000000..de55f9acdf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..847d54732e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-a-reference.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.rs
new file mode 100644
index 0000000000..d81f64d21b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..e4791d76b0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-nightly/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                          |
+   |                                          the trait `FromBytes` is not implemented for `NotZerocopy`
+   |                                          required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-nightly/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.rs
new file mode 100644
index 0000000000..625f1fac07
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.stderr
new file mode 100644
index 0000000000..3d0f6d0300
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-dst-unsized.stderr
@@ -0,0 +1,69 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                            |
+   |                            doesn't have a size known at compile-time
+   |                            required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                                ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.rs
new file mode 100644
index 0000000000..8dd191e6f4
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static u64 = zerocopy::transmute_ref!(&x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.stderr
new file mode 100644
index 0000000000..e16a557611
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-illegal-lifetime.stderr
@@ -0,0 +1,12 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-nightly/transmute-ref-illegal-lifetime.rs:14:52
+   |
+12 |     let x = 0u64;
+   |         - binding `x` declared here
+13 |     // It is illegal to increase the lifetime scope.
+14 |     let _: &'static u64 = zerocopy::transmute_ref!(&x);
+   |            ------------                            ^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.rs
new file mode 100644
index 0000000000..1d66a54ef7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.stderr
new file mode 100644
index 0000000000..793ecc54c0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-size-decrease.rs:17:28
+   |
+17 | const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.rs
new file mode 100644
index 0000000000..cdca560b30
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.stderr
new file mode 100644
index 0000000000..40c69f63c4
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-size-increase.rs:17:33
+   |
+17 | const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
+   |                                 ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.rs
new file mode 100644
index 0000000000..409d785b20
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes, U: FromBytes>(t: &T) -> &U {
+    // `transmute_ref!` requires the source and destination types to be
+    // concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.stderr
new file mode 100644
index 0000000000..6a3a4fd95b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.rs
new file mode 100644
index 0000000000..114e917b54
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.stderr
new file mode 100644
index 0000000000..0f1f7fc7b3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-not-references.stderr
@@ -0,0 +1,45 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-src-dst-not-references.rs:17:54
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ---------------^^^^^^-
+   |                                       |              |
+   |                                       |              expected `&_`, found `usize`
+   |                                       expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
+help: consider borrowing here
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(&0usize);
+   |                                                      +
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.rs
new file mode 100644
index 0000000000..6bfe7ffdfd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.stderr
new file mode 100644
index 0000000000..02e62bce0b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-dst-unsized.stderr
@@ -0,0 +1,183 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                                ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.rs
new file mode 100644
index 0000000000..010281c32e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes>(t: &T) -> &u8 {
+    // `transmute_ref!` requires the source type to be concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.stderr
new file mode 100644
index 0000000000..a168f44bb4
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, u8>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.rs
new file mode 100644
index 0000000000..90661b3e2c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.stderr
new file mode 100644
index 0000000000..be477c6c5e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-a-reference.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-nightly/transmute-ref-src-not-a-reference.rs:17:49
+   |
+17 | const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
+   |                                  ---------------^^^^^^-
+   |                                  |              |
+   |                                  |              expected `&_`, found `usize`
+   |                                  expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
+help: consider borrowing here
+   |
+17 | const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(&0usize);
+   |                                                 +
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.rs
new file mode 100644
index 0000000000..6ab19f3c82
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.stderr
new file mode 100644
index 0000000000..eb28ccf7c8
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                 |
+   |                                 the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |                                 required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.rs
new file mode 100644
index 0000000000..14e72b4ddc
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.stderr
new file mode 100644
index 0000000000..b280429b03
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-ref-src-unsized.stderr
@@ -0,0 +1,127 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-nightly/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.rs
new file mode 100644
index 0000000000..1d56831f22
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: u8 = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.stderr
new file mode 100644
index 0000000000..83742d7824
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-size-decrease.rs:19:27
+   |
+19 | const DECREASE_SIZE: u8 = transmute!(AU16(0));
+   |                           ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AU16` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.rs
new file mode 100644
index 0000000000..32f9363089
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: AU16 = transmute!(0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.stderr
new file mode 100644
index 0000000000..230bb17a77
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-nightly/transmute-size-increase.rs:19:29
+   |
+19 | const INCREASE_SIZE: AU16 = transmute!(0u8);
+   |                             ^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `AU16` (16 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.rs
new file mode 100644
index 0000000000..dd730216b6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.stderr
new file mode 100644
index 0000000000..b36a820686
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-nightly/transmute-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |                                required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-nightly/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-nightly/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.rs b/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.rs
new file mode 100644
index 0000000000..45b6138f47
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.rs
@@ -0,0 +1,12 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because `UnsafeCell<u32>: !FromBytes`.
+const NOT_FROM_BYTES: core::cell::UnsafeCell<u32> =
+    include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.stderr
new file mode 100644
index 0000000000..7e9a035dc3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/include_value_not_from_bytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `UnsafeCell<u32>: FromBytes` is not satisfied
+  --> tests/ui-stable/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     the trait `FromBytes` is not implemented for `UnsafeCell<u32>`
+   |     required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-stable/include_value_not_from_bytes.rs:12:5
+   |
+12 |     include_value!("../../testdata/include_value/data");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `$crate::transmute` which comes from the expansion of the macro `include_value` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.rs b/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.rs
new file mode 100644
index 0000000000..d87b30698b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.rs
@@ -0,0 +1,11 @@
+// Copyright 2022 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[macro_use]
+extern crate zerocopy;
+
+fn main() {}
+
+// Should fail because the file is 4 bytes long, not 8.
+const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
diff --git a/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.stderr b/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.stderr
new file mode 100644
index 0000000000..956d74c505
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/include_value_wrong_size.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/include_value_wrong_size.rs:11:25
+   |
+11 | const WRONG_SIZE: u64 = include_value!("../../testdata/include_value/data");
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 4]` (32 bits)
+   = note: target type: `u64` (64 bits)
+   = note: this error originates in the macro `$crate::transmute` which comes from the expansion of the macro `include_value` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.rs b/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.rs
new file mode 100644
index 0000000000..ea963907df
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.rs
@@ -0,0 +1,29 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// Since some macros from `macros.rs` are unused.
+#![allow(unused)]
+
+extern crate zerocopy;
+extern crate zerocopy_derive;
+
+include!("../../../src/macros.rs");
+
+use zerocopy::*;
+use zerocopy_derive::*;
+
+fn main() {}
+
+#[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+#[repr(transparent)]
+struct Foo<T>(T);
+
+impl_or_verify!(T => FromZeroes for Foo<T>);
+impl_or_verify!(T => FromBytes for Foo<T>);
+impl_or_verify!(T => AsBytes for Foo<T>);
+impl_or_verify!(T => Unaligned for Foo<T>);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.stderr b/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.stderr
new file mode 100644
index 0000000000..7737d67175
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/invalid-impls/invalid-impls.stderr
@@ -0,0 +1,107 @@
+error[E0277]: the trait bound `T: zerocopy::FromZeroes` is not satisfied
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:26:37
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   |                                     ^^^^^^ the trait `zerocopy::FromZeroes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::FromZeroes`
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:22:10
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |          ^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-stable/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-stable/invalid-impls/invalid-impls.rs:26:1
+   |
+26 | impl_or_verify!(T => FromZeroes for Foo<T>);
+   | ------------------------------------------- in this macro invocation
+   = note: this error originates in the derive macro `FromZeroes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+26 | impl_or_verify!(T: zerocopy::FromZeroes => FromZeroes for Foo<T>);
+   |                  ++++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::FromBytes` is not satisfied
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:27:36
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   |                                    ^^^^^^ the trait `zerocopy::FromBytes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::FromBytes`
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:22:22
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                      ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-stable/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-stable/invalid-impls/invalid-impls.rs:27:1
+   |
+27 | impl_or_verify!(T => FromBytes for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the derive macro `FromBytes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+27 | impl_or_verify!(T: zerocopy::FromBytes => FromBytes for Foo<T>);
+   |                  +++++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::AsBytes` is not satisfied
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:28:34
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   |                                  ^^^^^^ the trait `zerocopy::AsBytes` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::AsBytes`
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:22:33
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                 ^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-stable/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-stable/invalid-impls/invalid-impls.rs:28:1
+   |
+28 | impl_or_verify!(T => AsBytes for Foo<T>);
+   | ---------------------------------------- in this macro invocation
+   = note: this error originates in the derive macro `AsBytes` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+28 | impl_or_verify!(T: zerocopy::AsBytes => AsBytes for Foo<T>);
+   |                  +++++++++++++++++++
+
+error[E0277]: the trait bound `T: zerocopy::Unaligned` is not satisfied
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:29:36
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   |                                    ^^^^^^ the trait `zerocopy::Unaligned` is not implemented for `T`
+   |
+note: required for `Foo<T>` to implement `zerocopy::Unaligned`
+  --> tests/ui-stable/invalid-impls/invalid-impls.rs:22:42
+   |
+22 | #[derive(FromZeroes, FromBytes, AsBytes, Unaligned)]
+   |                                          ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
+note: required by a bound in `_::Subtrait`
+  --> tests/ui-stable/invalid-impls/../../../src/macros.rs
+   |
+   |             trait Subtrait: $trait {}
+   |                             ^^^^^^ required by this bound in `Subtrait`
+   |
+  ::: tests/ui-stable/invalid-impls/invalid-impls.rs:29:1
+   |
+29 | impl_or_verify!(T => Unaligned for Foo<T>);
+   | ------------------------------------------ in this macro invocation
+   = note: this error originates in the derive macro `Unaligned` which comes from the expansion of the macro `impl_or_verify` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider restricting type parameter `T`
+   |
+29 | impl_or_verify!(T: zerocopy::Unaligned => Unaligned for Foo<T>);
+   |                  +++++++++++++++++++++
diff --git a/third_party/rust/zerocopy/tests/ui-stable/max-align.rs b/third_party/rust/zerocopy/tests/ui-stable/max-align.rs
new file mode 100644
index 0000000000..53e3eb9b0a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/max-align.rs
@@ -0,0 +1,99 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+#[repr(C, align(1))]
+struct Align1;
+
+#[repr(C, align(2))]
+struct Align2;
+
+#[repr(C, align(4))]
+struct Align4;
+
+#[repr(C, align(8))]
+struct Align8;
+
+#[repr(C, align(16))]
+struct Align16;
+
+#[repr(C, align(32))]
+struct Align32;
+
+#[repr(C, align(64))]
+struct Align64;
+
+#[repr(C, align(128))]
+struct Align128;
+
+#[repr(C, align(256))]
+struct Align256;
+
+#[repr(C, align(512))]
+struct Align512;
+
+#[repr(C, align(1024))]
+struct Align1024;
+
+#[repr(C, align(2048))]
+struct Align2048;
+
+#[repr(C, align(4096))]
+struct Align4096;
+
+#[repr(C, align(8192))]
+struct Align8192;
+
+#[repr(C, align(16384))]
+struct Align16384;
+
+#[repr(C, align(32768))]
+struct Align32768;
+
+#[repr(C, align(65536))]
+struct Align65536;
+
+#[repr(C, align(131072))]
+struct Align131072;
+
+#[repr(C, align(262144))]
+struct Align262144;
+
+#[repr(C, align(524288))]
+struct Align524288;
+
+#[repr(C, align(1048576))]
+struct Align1048576;
+
+#[repr(C, align(2097152))]
+struct Align2097152;
+
+#[repr(C, align(4194304))]
+struct Align4194304;
+
+#[repr(C, align(8388608))]
+struct Align8388608;
+
+#[repr(C, align(16777216))]
+struct Align16777216;
+
+#[repr(C, align(33554432))]
+struct Align33554432;
+
+#[repr(C, align(67108864))]
+struct Align67108864;
+
+#[repr(C, align(134217728))]
+struct Align13421772;
+
+#[repr(C, align(268435456))]
+struct Align26843545;
+
+#[repr(C, align(1073741824))]
+struct Align1073741824;
+
+fn main() {}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/max-align.stderr b/third_party/rust/zerocopy/tests/ui-stable/max-align.stderr
new file mode 100644
index 0000000000..ea472f2df7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/max-align.stderr
@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-stable/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.rs
new file mode 100644
index 0000000000..c4caaff917
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..b008bcdb10
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-stable/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^
+   |                                         |
+   |                                         the trait `FromBytes` is not implemented for `NotZerocopy`
+   |                                         required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-stable/transmute-dst-not-frombytes.rs:18:41
+   |
+18 | const DST_NOT_FROM_BYTES: NotZerocopy = transmute!(AU16(0));
+   |                                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.rs
new file mode 100644
index 0000000000..0928564dd5
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.stderr
new file mode 100644
index 0000000000..252fec9ef8
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-alignment-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-alignment-increase.rs:19:39
+   |
+19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.rs
new file mode 100644
index 0000000000..021b562f18
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.rs
@@ -0,0 +1,20 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+
+// `transmute_mut!` cannot, generally speaking, be used in const contexts.
+const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.stderr
new file mode 100644
index 0000000000..a89ea67558
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-const.stderr
@@ -0,0 +1,41 @@
+warning: taking a mutable reference to a `const` item
+  --> tests/ui-stable/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: each usage of a `const` item creates a new temporary
+   = note: the mutable reference will refer to this temporary, not the original `const` item
+note: `const` item defined here
+  --> tests/ui-stable/transmute-mut-const.rs:17:1
+   |
+17 | const ARRAY_OF_U8S: [u8; 2] = [0u8; 2];
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[warn(const_item_mutation)]` on by default
+
+error[E0658]: mutable references are not allowed in constants
+  --> tests/ui-stable/transmute-mut-const.rs:20:52
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                                    ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
+
+error[E0015]: cannot call non-const fn `transmute_mut::<'_, '_, [u8; 2], [u8; 2]>` in constants
+  --> tests/ui-stable/transmute-mut-const.rs:20:37
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> tests/ui-stable/transmute-mut-const.rs:20:57
+   |
+20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
+   |                                     --------------------^^^^^^^^^^^^-
+   |                                     |                   |
+   |                                     |                   creates a temporary value which is freed while still in use
+   |                                     temporary value is freed at the end of this statement
+   |                                     using this value as a constant requires that borrow lasts for `'static`
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.rs
new file mode 100644
index 0000000000..7068f1026d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(u: &mut u8) -> &mut T {
+    // `transmute_mut!` requires the destination type to be concrete.
+    transmute_mut!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.stderr
new file mode 100644
index 0000000000..0000eb0bab
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-dst-generic.rs:17:5
+   |
+17 |     transmute_mut!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.rs
new file mode 100644
index 0000000000..33a9ecd955
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..14ee444cc5
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-a-reference.stderr
@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_mut!(&mut 0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&mut _`
+   |
+   = note:           expected type `usize`
+           found mutable reference `&mut _`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.rs
new file mode 100644
index 0000000000..b72f12928c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `AsBytes`
+const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.stderr
new file mode 100644
index 0000000000..f3cacca09d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-asbytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Dst: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    the trait `AsBytes` is not implemented for `Dst`
+   |                                    required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-stable/transmute-mut-dst-not-asbytes.rs:24:36
+   |
+24 | const DST_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.rs
new file mode 100644
index 0000000000..102fcedc9a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..39bb4fd96d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `Dst: FromBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                      |
+   |                                      the trait `FromBytes` is not implemented for `Dst`
+   |                                      required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-stable/transmute-mut-dst-not-frombytes.rs:24:38
+   |
+24 | const DST_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.rs
new file mode 100644
index 0000000000..693ccda56f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.stderr
new file mode 100644
index 0000000000..07727850cd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-dst-unsized.stderr
@@ -0,0 +1,106 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-dst-unsized.rs:17:32
+   |
+17 | const DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8; 1]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                          ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.rs
new file mode 100644
index 0000000000..c31765e4b9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let mut x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.stderr
new file mode 100644
index 0000000000..7f128138f3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-illegal-lifetime.stderr
@@ -0,0 +1,12 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-stable/transmute-mut-illegal-lifetime.rs:14:56
+   |
+12 |     let mut x = 0u64;
+   |         ----- binding `x` declared here
+13 |     // It is illegal to increase the lifetime scope.
+14 |     let _: &'static mut u64 = zerocopy::transmute_mut!(&mut x);
+   |            ----------------                            ^^^^^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.rs
new file mode 100644
index 0000000000..c6eec3a9c2
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// We require that the size of the destination type is not smaller than the size
+// of the source type.
+const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.stderr
new file mode 100644
index 0000000000..239991357d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-size-decrease.rs:17:32
+   |
+17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.rs
new file mode 100644
index 0000000000..a4657c2838
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.stderr
new file mode 100644
index 0000000000..1427c7b0e9
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-size-increase.rs:17:37
+   |
+17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.rs
new file mode 100644
index 0000000000..aed7ded96f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes, U: AsBytes + FromBytes>(t: &mut T) -> &mut U {
+    // `transmute_mut!` requires the source and destination types to be
+    // concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.stderr
new file mode 100644
index 0000000000..ddb8bb6fe7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-mut-src-dst-generic.rs:18:5
+   |
+18 |     transmute_mut!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.rs
new file mode 100644
index 0000000000..98cc520889
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.stderr
new file mode 100644
index 0000000000..c0d9e0f0d3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-not-references.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-src-dst-not-references.rs:17:59
+   |
+17 | const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(0usize);
+   |                                            ---------------^^^^^^-
+   |                                            |              |
+   |                                            |              expected `&mut _`, found `usize`
+   |                                            expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
+help: consider mutably borrowing here
+   |
+17 | const SRC_DST_NOT_REFERENCES: &mut usize = transmute_mut!(&mut 0usize);
+   |                                                           ++++
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.rs
new file mode 100644
index 0000000000..1bebcf2d68
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.stderr
new file mode 100644
index 0000000000..8cf76649eb
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-dst-unsized.stderr
@@ -0,0 +1,288 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertDstIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertDstIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                      ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    doesn't have a size known at compile-time
+   |                                    required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-dst-unsized.rs:17:36
+   |
+17 | const SRC_DST_UNSIZED: &mut [u8] = transmute_mut!(&mut [0u8][..]);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                          ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.rs
new file mode 100644
index 0000000000..a3ef397876
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_mut, AsBytes};
+
+fn main() {}
+
+fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+    // `transmute_mut!` requires the source type to be concrete.
+    transmute_mut!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.stderr
new file mode 100644
index 0000000000..fc4809e418
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-generic.stderr
@@ -0,0 +1,10 @@
+error[E0405]: cannot find trait `FromBytes` in this scope
+  --> tests/ui-stable/transmute-mut-src-generic.rs:15:31
+   |
+15 | fn transmute_mut<T: AsBytes + FromBytes>(t: &mut T) -> &mut u8 {
+   |                               ^^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+11 + use zerocopy::FromBytes;
+   |
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.rs
new file mode 100644
index 0000000000..08088d0db6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+fn ref_src_immutable() {
+    // `transmute_mut!` requires that its source type be a mutable reference.
+    let _: &mut u8 = transmute_mut!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.stderr
new file mode 100644
index 0000000000..0115c791d3
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-immutable.stderr
@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-src-immutable.rs:17:37
+   |
+17 |     let _: &mut u8 = transmute_mut!(&0u8);
+   |                      ---------------^^^^-
+   |                      |              |
+   |                      |              types differ in mutability
+   |                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                      found reference `&u8`
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.rs
new file mode 100644
index 0000000000..bf8bc32592
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.stderr
new file mode 100644
index 0000000000..8c1d9b47ba
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-a-reference.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-mut-src-not-a-reference.rs:17:53
+   |
+17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(0usize);
+   |                                      ---------------^^^^^^-
+   |                                      |              |
+   |                                      |              expected `&mut _`, found `usize`
+   |                                      expected due to this
+   |
+   = note: expected mutable reference `&mut _`
+                           found type `usize`
+help: consider mutably borrowing here
+   |
+17 | const SRC_NOT_A_REFERENCE: &mut u8 = transmute_mut!(&mut 0usize);
+   |                                                     ++++
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.rs
new file mode 100644
index 0000000000..6a14f12fd0
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.stderr
new file mode 100644
index 0000000000..9fc954654e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                    |
+   |                                    the trait `AsBytes` is not implemented for `Src`
+   |                                    required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `Src`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-not-asbytes.rs:24:36
+   |
+24 | const SRC_NOT_AS_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.rs
new file mode 100644
index 0000000000..2ebe03601b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.rs
@@ -0,0 +1,24 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+#[derive(zerocopy::AsBytes)]
+#[repr(C)]
+struct Src;
+
+#[derive(zerocopy::FromZeroes, zerocopy::FromBytes, zerocopy::AsBytes)]
+#[repr(C)]
+struct Dst;
+
+// `transmute_mut` requires that the source type implements `FromBytes`
+const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.stderr
new file mode 100644
index 0000000000..cc4a19d724
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-not-frombytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                      |
+   |                                      the trait `FromBytes` is not implemented for `Src`
+   |                                      required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `Src: FromBytes` is not satisfied
+  --> tests/ui-stable/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes` is not implemented for `Src`
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-not-frombytes.rs:24:38
+   |
+24 | const SRC_NOT_FROM_BYTES: &mut Dst = transmute_mut!(&mut Src);
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.rs
new file mode 100644
index 0000000000..413dd68d89
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_mut;
+
+fn main() {}
+
+// `transmute_mut!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.stderr
new file mode 100644
index 0000000000..7f6def929d
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-mut-src-unsized.stderr
@@ -0,0 +1,195 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsFromBytes`
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsFromBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertSrcIsAsBytes`
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertSrcIsAsBytes`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                      ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-mut-src-unsized.rs:16:35
+   |
+16 | const SRC_UNSIZED: &mut [u8; 1] = transmute_mut!(&mut [0u8][..]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                   |
+   |                                   doesn't have a size known at compile-time
+   |                                   required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_mut`
+  --> src/macro_util.rs
+   |
+   | pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                               ^^^ required by this bound in `transmute_mut`
+   = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.rs
new file mode 100644
index 0000000000..5af8859332
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.rs
@@ -0,0 +1,20 @@
+// Copyright 2022 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// It is unclear whether we can or should support this transmutation, especially
+// in a const context. This test ensures that even if such a transmutation
+// becomes valid due to the requisite implementations of `FromBytes` being
+// added, that we re-examine whether it should specifically be valid in a const
+// context.
+const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.stderr
new file mode 100644
index 0000000000..4f4d583dbe
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ptr-to-usize.stderr
@@ -0,0 +1,30 @@
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                              |
+   |                              the trait `AsBytes` is not implemented for `*const usize`
+   |                              required by a bound introduced by this call
+   |
+   = help: the trait `AsBytes` is implemented for `usize`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
+   |
+   = help: the trait `AsBytes` is implemented for `usize`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ptr-to-usize.rs:20:30
+   |
+20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.rs
new file mode 100644
index 0000000000..bf1988c66b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a type of smaller
+// alignment to one of larger alignment.
+const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.stderr
new file mode 100644
index 0000000000..a34c4065d1
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-alignment-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-alignment-increase.rs:19:35
+   |
+19 | const INCREASE_ALIGNMENT: &AU16 = transmute_ref!(&[0u8; 2]);
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<[u8; 2]>` (8 bits)
+   = note: target type: `MaxAlignsOf<[u8; 2], AU16>` (16 bits)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.rs
new file mode 100644
index 0000000000..bf4a0f9adf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: FromBytes>(u: &u8) -> &T {
+    // `transmute_ref!` requires the destination type to be concrete.
+    transmute_ref!(u)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.stderr
new file mode 100644
index 0000000000..e30b9f67a6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `T` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-dst-generic.rs:17:5
+   |
+17 |     transmute_ref!(u)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<u8>` (8 bits)
+   = note: target type: `MaxAlignsOf<u8, T>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.rs
new file mode 100644
index 0000000000..fa0e6e4c9b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+fn ref_dst_mutable() {
+    // `transmute_ref!` requires that its destination type be an immutable
+    // reference.
+    let _: &mut u8 = transmute_ref!(&0u8);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.stderr
new file mode 100644
index 0000000000..c70f6ea618
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-mutable.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-mutable.rs:18:22
+   |
+18 |     let _: &mut u8 = transmute_ref!(&0u8);
+   |                      ^^^^^^^^^^^^^^^^^^^^ types differ in mutability
+   |
+   = note: expected mutable reference `&mut u8`
+                      found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.rs
new file mode 100644
index 0000000000..de55f9acdf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into a non-reference
+// destination type.
+const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.stderr
new file mode 100644
index 0000000000..ab3f90c2fd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-a-reference.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-dst-not-a-reference.rs:17:36
+   |
+17 | const DST_NOT_A_REFERENCE: usize = transmute_ref!(&0u8);
+   |                                    ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.rs
new file mode 100644
index 0000000000..d81f64d21b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the destination type implements `FromBytes`
+const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.stderr
new file mode 100644
index 0000000000..76d18c5e45
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-not-frombytes.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `NotZerocopy: FromBytes` is not satisfied
+  --> tests/ui-stable/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                          |
+   |                                          the trait `FromBytes` is not implemented for `NotZerocopy`
+   |                                          required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `FromBytes`:
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+             usize
+             u8
+           and $N others
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-stable/transmute-ref-dst-not-frombytes.rs:18:42
+   |
+18 | const DST_NOT_FROM_BYTES: &NotZerocopy = transmute_ref!(&AU16(0));
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.rs
new file mode 100644
index 0000000000..625f1fac07
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting into an unsized destination
+// type.
+const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.stderr
new file mode 100644
index 0000000000..8a0c761466
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-dst-unsized.stderr
@@ -0,0 +1,89 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                            |
+   |                            doesn't have a size known at compile-time
+   |                            required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                          ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                            |
+   |                            doesn't have a size known at compile-time
+   |                            required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-dst-unsized.rs:17:28
+   |
+17 | const DST_UNSIZED: &[u8] = transmute_ref!(&[0u8; 1]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                                ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.rs
new file mode 100644
index 0000000000..8dd191e6f4
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+fn main() {}
+
+fn increase_lifetime() {
+    let x = 0u64;
+    // It is illegal to increase the lifetime scope.
+    let _: &'static u64 = zerocopy::transmute_ref!(&x);
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.stderr
new file mode 100644
index 0000000000..1ef34feb7f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-illegal-lifetime.stderr
@@ -0,0 +1,12 @@
+error[E0597]: `x` does not live long enough
+  --> tests/ui-stable/transmute-ref-illegal-lifetime.rs:14:52
+   |
+12 |     let x = 0u64;
+   |         - binding `x` declared here
+13 |     // It is illegal to increase the lifetime scope.
+14 |     let _: &'static u64 = zerocopy::transmute_ref!(&x);
+   |            ------------                            ^^ borrowed value does not live long enough
+   |            |
+   |            type annotation requires that `x` is borrowed for `'static`
+15 | }
+   | - `x` dropped here while still borrowed
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.rs
new file mode 100644
index 0000000000..1d66a54ef7
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.stderr
new file mode 100644
index 0000000000..f353b26ece
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-size-decrease.rs:17:28
+   |
+17 | const DECREASE_SIZE: &u8 = transmute_ref!(&[0u8; 2]);
+   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; 2]` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.rs
new file mode 100644
index 0000000000..cdca560b30
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.stderr
new file mode 100644
index 0000000000..f51eb63f4b
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-size-increase.rs:17:33
+   |
+17 | const INCREASE_SIZE: &[u8; 2] = transmute_ref!(&0u8);
+   |                                 ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `[u8; 2]` (16 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.rs
new file mode 100644
index 0000000000..409d785b20
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes, FromBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes, U: FromBytes>(t: &T) -> &U {
+    // `transmute_ref!` requires the source and destination types to be
+    // concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.stderr
new file mode 100644
index 0000000000..0905dc6d5f
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `U` (this type does not have a fixed size)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-src-dst-generic.rs:18:5
+   |
+18 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, U>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.rs
new file mode 100644
index 0000000000..114e917b54
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between non-reference source
+// and destination types.
+const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.stderr
new file mode 100644
index 0000000000..8a80e991e6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-not-references.stderr
@@ -0,0 +1,45 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-src-dst-not-references.rs:17:54
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ---------------^^^^^^-
+   |                                       |              |
+   |                                       |              expected `&_`, found `usize`
+   |                                       expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
+help: consider borrowing here
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(&0usize);
+   |                                                      +
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-src-dst-not-references.rs:17:39
+   |
+17 | const SRC_DST_NOT_REFERENCES: usize = transmute_ref!(0usize);
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `&_`
+   |
+   = note:   expected type `usize`
+           found reference `&_`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.rs
new file mode 100644
index 0000000000..6bfe7ffdfd
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting between unsized source and
+// destination types.
+const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.stderr
new file mode 100644
index 0000000000..ca62fcf7db
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-dst-unsized.stderr
@@ -0,0 +1,240 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsFromBytes`
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsFromBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                      ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                           ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |         ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                doesn't have a size known at compile-time
+   |                                required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-dst-unsized.rs:17:32
+   |
+17 | const SRC_DST_UNSIZED: &[u8] = transmute_ref!(&[0u8][..]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                                ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.rs
new file mode 100644
index 0000000000..010281c32e
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::{transmute_ref, AsBytes};
+
+fn main() {}
+
+fn transmute_ref<T: AsBytes>(t: &T) -> &u8 {
+    // `transmute_ref!` requires the source type to be concrete.
+    transmute_ref!(t)
+}
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.stderr
new file mode 100644
index 0000000000..b6bbd1648a
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-generic.stderr
@@ -0,0 +1,19 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `T` (this type does not have a fixed size)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-ref-src-generic.rs:17:5
+   |
+17 |     transmute_ref!(t)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AlignOf<T>` (size can vary because of T)
+   = note: target type: `MaxAlignsOf<T, u8>` (size can vary because of T)
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.rs
new file mode 100644
index 0000000000..90661b3e2c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.rs
@@ -0,0 +1,17 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from a non-reference source
+// type.
+const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.stderr
new file mode 100644
index 0000000000..622c3db9ac
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-a-reference.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> tests/ui-stable/transmute-ref-src-not-a-reference.rs:17:49
+   |
+17 | const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(0usize);
+   |                                  ---------------^^^^^^-
+   |                                  |              |
+   |                                  |              expected `&_`, found `usize`
+   |                                  expected due to this
+   |
+   = note: expected reference `&_`
+                   found type `usize`
+help: consider borrowing here
+   |
+17 | const SRC_NOT_A_REFERENCE: &u8 = transmute_ref!(&0usize);
+   |                                                 +
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.rs
new file mode 100644
index 0000000000..6ab19f3c82
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.stderr
new file mode 100644
index 0000000000..2ded6baa03
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                 |
+   |                                 the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |                                 required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-not-asbytes.rs:18:33
+   |
+18 | const SRC_NOT_AS_BYTES: &AU16 = transmute_ref!(&NotZerocopy(AU16(0)));
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.rs
new file mode 100644
index 0000000000..14e72b4ddc
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.rs
@@ -0,0 +1,16 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+extern crate zerocopy;
+
+use zerocopy::transmute_ref;
+
+fn main() {}
+
+// `transmute_ref!` does not support transmuting from an unsized source type.
+const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.stderr
new file mode 100644
index 0000000000..b194d67473
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-ref-src-unsized.stderr
@@ -0,0 +1,164 @@
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute`
+  --> $RUST/core/src/intrinsics.rs
+   |
+   |     pub fn transmute<Src, Dst>(src: Src) -> Dst;
+   |                      ^^^ required by this bound in `transmute`
+   = note: this error originates in the macro `$crate::assert_size_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf::<T>::into_t`
+  --> src/macro_util.rs
+   |
+   | impl<T> AlignOf<T> {
+   |      ^ required by this bound in `AlignOf::<T>::into_t`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn into_t(self) -> T {
+   |            ------ required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+   = note: the left-hand-side of an assignment must have a statically known size
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf::<T, U>::new`
+  --> src/macro_util.rs
+   |
+   | impl<T, U> MaxAlignsOf<T, U> {
+   |      ^ required by this bound in `MaxAlignsOf::<T, U>::new`
+   |     #[inline(never)] // Make `missing_inline_in_public_items` happy.
+   |     pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
+   |            --- required by a bound in this associated function
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `MaxAlignsOf`
+  --> src/macro_util.rs
+   |
+   | pub union MaxAlignsOf<T, U> {
+   |                       ^ required by this bound in `MaxAlignsOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `AlignOf`
+  --> src/macro_util.rs
+   |
+   | pub struct AlignOf<T> {
+   |                    ^ required by this bound in `AlignOf`
+   = note: this error originates in the macro `$crate::assert_align_gt_eq` which comes from the expansion of the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> tests/ui-stable/transmute-ref-src-unsized.rs:16:31
+   |
+16 | const SRC_UNSIZED: &[u8; 1] = transmute_ref!(&[0u8][..]);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                               |
+   |                               doesn't have a size known at compile-time
+   |                               required by a bound introduced by this call
+   |
+   = help: the trait `Sized` is not implemented for `[u8]`
+note: required by a bound in `transmute_ref`
+  --> src/macro_util.rs
+   |
+   | pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
+   |                                                     ^^^ required by this bound in `transmute_ref`
+   = note: this error originates in the macro `transmute_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.rs
new file mode 100644
index 0000000000..1d56831f22
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// Although this is not a soundness requirement, we currently require that the
+// size of the destination type is not smaller than the size of the source type.
+const DECREASE_SIZE: u8 = transmute!(AU16(0));
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.stderr
new file mode 100644
index 0000000000..0241662fdf
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-decrease.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-size-decrease.rs:19:27
+   |
+19 | const DECREASE_SIZE: u8 = transmute!(AU16(0));
+   |                           ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `AU16` (16 bits)
+   = note: target type: `u8` (8 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.rs
new file mode 100644
index 0000000000..32f9363089
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.rs
@@ -0,0 +1,19 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute!` does not support transmuting from a smaller type to a larger
+// one.
+const INCREASE_SIZE: AU16 = transmute!(0u8);
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.stderr
new file mode 100644
index 0000000000..87d82a208c
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-size-increase.stderr
@@ -0,0 +1,9 @@
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> tests/ui-stable/transmute-size-increase.rs:19:29
+   |
+19 | const INCREASE_SIZE: AU16 = transmute!(0u8);
+   |                             ^^^^^^^^^^^^^^^
+   |
+   = note: source type: `u8` (8 bits)
+   = note: target type: `AU16` (16 bits)
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.rs b/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.rs
new file mode 100644
index 0000000000..dd730216b6
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.rs
@@ -0,0 +1,18 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+include!("../../zerocopy-derive/tests/util.rs");
+
+extern crate zerocopy;
+
+use zerocopy::transmute;
+
+fn main() {}
+
+// `transmute` requires that the source type implements `AsBytes`
+const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
diff --git a/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.stderr b/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.stderr
new file mode 100644
index 0000000000..f2e834eb57
--- /dev/null
+++ b/third_party/rust/zerocopy/tests/ui-stable/transmute-src-not-asbytes.stderr
@@ -0,0 +1,48 @@
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                |
+   |                                the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |                                required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: the trait bound `NotZerocopy<AU16>: AsBytes` is not satisfied
+  --> tests/ui-stable/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `NotZerocopy<AU16>`
+   |
+   = help: the following other types implement trait `AsBytes`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others
+note: required by a bound in `AssertIsAsBytes`
+  --> tests/ui-stable/transmute-src-not-asbytes.rs:18:32
+   |
+18 | const SRC_NOT_AS_BYTES: AU16 = transmute!(NotZerocopy(AU16(0)));
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `AssertIsAsBytes`
+   = note: this error originates in the macro `transmute` (in Nightly builds, run with -Z macro-backtrace for more info)