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diff --git a/mozglue/static/rust/moz_asserts/lib.rs b/mozglue/static/rust/moz_asserts/lib.rs
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+++ b/mozglue/static/rust/moz_asserts/lib.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// Implementation note: It seems tempting to use if cfg!(feature = ...) directly
+// in the macro, but that doesn't work, as the feature would be evaluated
+// against the dependent crate.
+//
+// It'd also seem tempting to export different macros depending on the features
+// enabled, but that's also not great because it causes warnings when the
+// features are enabled, e.g.:
+//
+//   nightly_panic!("foo");
+//   return SAFE_VALUE;
+//
+// would cause an unreachable code warning for Nightly builds. So instead we
+// choose an exported constant to guard the condition. (For reference, this
+// is also how rust's `debug_assert!` is implemented)
+
+/// Whether Nightly-only assertions are enabled.
+pub use mozbuild::config::NIGHTLY_BUILD;
+
+/// Whether diagnostic assertions are enabled.
+pub use mozbuild::config::MOZ_DIAGNOSTIC_ASSERT_ENABLED;
+
+/// assert! on Nightly, gets compiled out otherwise.
+#[macro_export]
+macro_rules! nightly_assert {
+    ($($arg:tt)*) => (if $crate::NIGHTLY_BUILD { assert!($($arg)*); })
+}
+
+/// assert_eq! on Nightly, gets compiled out otherwise.
+#[macro_export]
+macro_rules! nightly_assert_eq {
+    ($($arg:tt)*) => (if $crate::NIGHTLY_BUILD { assert_eq!($($arg)*); })
+}
+
+/// assert_ne! on Nightly, gets compiled out otherwise.
+#[macro_export]
+macro_rules! nightly_assert_ne {
+    ($($arg:tt)*) => (if $crate::NIGHTLY_BUILD { assert_ne!($($arg)*); })
+}
+
+/// panic! on Nightly, gets compiled out otherwise.
+#[macro_export]
+macro_rules! nightly_panic {
+    ($($arg:tt)*) => (if $crate::NIGHTLY_BUILD { panic!($($arg)*); })
+}
+
+/// unreachable! on Nightly, `std::hint::unreachable_unchecked()` otherwise.
+///
+/// Use carefully! Consider using nightly_panic! and handling the failure
+/// gracefully if you can't prove it's really unreachable.
+///
+/// See https://doc.rust-lang.org/std/hint/fn.unreachable_unchecked.html#safety
+/// for safety details.
+#[macro_export]
+macro_rules! nightly_unreachable {
+    ($($arg:tt)*) => {
+        if $crate::NIGHTLY_BUILD {
+            unreachable!($($arg)*);
+        } else {
+            std::hint::unreachable_unchecked()
+        }
+    }
+}
+
+/// assert! when diagnostic asserts are enabled, gets compiled out otherwise.
+#[macro_export]
+macro_rules! diagnostic_assert {
+    ($($arg:tt)*) => (if $crate::MOZ_DIAGNOSTIC_ASSERT_ENABLED { assert!($($arg)*); })
+}
+
+/// assert_eq! when diagnostic asserts are enabled, gets compiled out otherwise.
+#[macro_export]
+macro_rules! diagnostic_assert_eq {
+    ($($arg:tt)*) => (if $crate::MOZ_DIAGNOSTIC_ASSERT_ENABLED { assert_eq!($($arg)*); })
+}
+
+/// assert_ne! when diagnostic asserts are enabled, gets compiled out otherwise.
+#[macro_export]
+macro_rules! diagnostic_assert_ne {
+    ($($arg:tt)*) => (if $crate::MOZ_DIAGNOSTIC_ASSERT_ENABLED { assert_ne!($($arg)*); })
+}
+
+/// unreachable! when diagnostic asserts are enabled,
+/// `std::hint::unreachable_unchecked()` otherwise.
+///
+/// Use carefully! Consider using diagnostic_panic! and handling the failure
+/// gracefully if you can't prove it's really unreachable.
+///
+/// See https://doc.rust-lang.org/std/hint/fn.unreachable_unchecked.html#safety
+/// for safety details.
+#[macro_export]
+macro_rules! diagnostic_unreachable {
+    ($($arg:tt)*) => {
+        if $crate::MOZ_DIAGNOSTIC_ASSERT_ENABLED {
+            unreachable!($($arg)*);
+        } else {
+            std::hint::unreachable_unchecked()
+        }
+    }
+}