From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:02:58 +0200
Subject: Adding upstream version 1.64.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../auxiliary/specialization-trait.rs              |  6 ++++
 .../min_specialization/dyn-trait-assoc-types.rs    | 32 ++++++++++++++++++++++
 .../dyn-trait-assoc-types.stderr                   | 14 ++++++++++
 .../min_specialization/impl-on-nonexisting.rs      |  7 +++++
 .../min_specialization/impl-on-nonexisting.stderr  |  9 ++++++
 .../impl_specialization_trait.rs                   | 16 +++++++++++
 .../impl_specialization_trait.stderr               | 10 +++++++
 .../implcit-well-formed-bounds.rs                  | 30 ++++++++++++++++++++
 .../min_specialization/issue-79224.rs              | 24 ++++++++++++++++
 .../min_specialization/issue-79224.stderr          | 27 ++++++++++++++++++
 .../min_specialization/repeated_projection_type.rs | 24 ++++++++++++++++
 .../repeated_projection_type.stderr                |  8 ++++++
 .../min_specialization/repeating_lifetimes.rs      | 19 +++++++++++++
 .../min_specialization/repeating_lifetimes.stderr  |  8 ++++++
 .../min_specialization/repeating_param.rs          | 17 ++++++++++++
 .../min_specialization/repeating_param.stderr      |  8 ++++++
 .../specialization/min_specialization/spec-iter.rs | 20 ++++++++++++++
 .../min_specialization/spec-marker-supertraits.rs  | 29 ++++++++++++++++++++
 .../spec-marker-supertraits.stderr                 |  8 ++++++
 .../min_specialization/spec-reference.rs           | 19 +++++++++++++
 .../min_specialization/specialization_marker.rs    | 17 ++++++++++++
 .../specialization_marker.stderr                   | 15 ++++++++++
 .../specialization_super_trait.rs                  | 18 ++++++++++++
 .../specialization_super_trait.stderr              |  8 ++++++
 .../min_specialization/specialization_trait.rs     | 26 ++++++++++++++++++
 .../min_specialization/specialization_trait.stderr | 20 ++++++++++++++
 .../min_specialization/specialize_on_marker.rs     | 24 ++++++++++++++++
 .../min_specialization/specialize_on_spec_trait.rs | 27 ++++++++++++++++++
 .../min_specialization/specialize_on_static.rs     | 18 ++++++++++++
 .../min_specialization/specialize_on_static.stderr |  8 ++++++
 .../min_specialization/specialize_on_trait.rs      | 20 ++++++++++++++
 .../min_specialization/specialize_on_trait.stderr  |  8 ++++++
 32 files changed, 544 insertions(+)
 create mode 100644 src/test/ui/specialization/min_specialization/auxiliary/specialization-trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.rs
 create mode 100644 src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/impl-on-nonexisting.rs
 create mode 100644 src/test/ui/specialization/min_specialization/impl-on-nonexisting.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/impl_specialization_trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/impl_specialization_trait.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/implcit-well-formed-bounds.rs
 create mode 100644 src/test/ui/specialization/min_specialization/issue-79224.rs
 create mode 100644 src/test/ui/specialization/min_specialization/issue-79224.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/repeated_projection_type.rs
 create mode 100644 src/test/ui/specialization/min_specialization/repeated_projection_type.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/repeating_lifetimes.rs
 create mode 100644 src/test/ui/specialization/min_specialization/repeating_lifetimes.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/repeating_param.rs
 create mode 100644 src/test/ui/specialization/min_specialization/repeating_param.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/spec-iter.rs
 create mode 100644 src/test/ui/specialization/min_specialization/spec-marker-supertraits.rs
 create mode 100644 src/test/ui/specialization/min_specialization/spec-marker-supertraits.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/spec-reference.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_marker.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_marker.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_super_trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_super_trait.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialization_trait.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_marker.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_spec_trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_static.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_static.stderr
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_trait.rs
 create mode 100644 src/test/ui/specialization/min_specialization/specialize_on_trait.stderr

(limited to 'src/test/ui/specialization/min_specialization')

diff --git a/src/test/ui/specialization/min_specialization/auxiliary/specialization-trait.rs b/src/test/ui/specialization/min_specialization/auxiliary/specialization-trait.rs
new file mode 100644
index 000000000..6ec0d261d
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/auxiliary/specialization-trait.rs
@@ -0,0 +1,6 @@
+#![feature(rustc_attrs)]
+
+#[rustc_specialization_trait]
+pub trait SpecTrait {
+    fn method(&self);
+}
diff --git a/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.rs b/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.rs
new file mode 100644
index 000000000..03cab00b0
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.rs
@@ -0,0 +1,32 @@
+// Test that associated types in trait objects are not considered to be
+// constrained.
+
+#![feature(min_specialization)]
+
+trait Specializable {
+    fn f();
+}
+
+trait B<T> {
+    type Y;
+}
+
+trait C {
+    type Y;
+}
+
+impl<A: ?Sized> Specializable for A {
+    default fn f() {}
+}
+
+impl<'a, T> Specializable for dyn B<T, Y = T> + 'a {
+    //~^ ERROR specializing impl repeats parameter `T`
+    fn f() {}
+}
+
+impl<'a, T> Specializable for dyn C<Y = (T, T)> + 'a {
+    //~^ ERROR specializing impl repeats parameter `T`
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.stderr b/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.stderr
new file mode 100644
index 000000000..db5558f16
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/dyn-trait-assoc-types.stderr
@@ -0,0 +1,14 @@
+error: specializing impl repeats parameter `T`
+  --> $DIR/dyn-trait-assoc-types.rs:22:1
+   |
+LL | impl<'a, T> Specializable for dyn B<T, Y = T> + 'a {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: specializing impl repeats parameter `T`
+  --> $DIR/dyn-trait-assoc-types.rs:27:1
+   |
+LL | impl<'a, T> Specializable for dyn C<Y = (T, T)> + 'a {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/specialization/min_specialization/impl-on-nonexisting.rs b/src/test/ui/specialization/min_specialization/impl-on-nonexisting.rs
new file mode 100644
index 000000000..77a64320d
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/impl-on-nonexisting.rs
@@ -0,0 +1,7 @@
+#![feature(min_specialization)]
+
+trait Trait {}
+impl Trait for NonExistent {}
+//~^ ERROR cannot find type `NonExistent` in this scope
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/impl-on-nonexisting.stderr b/src/test/ui/specialization/min_specialization/impl-on-nonexisting.stderr
new file mode 100644
index 000000000..b032ccbe5
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/impl-on-nonexisting.stderr
@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `NonExistent` in this scope
+  --> $DIR/impl-on-nonexisting.rs:4:16
+   |
+LL | impl Trait for NonExistent {}
+   |                ^^^^^^^^^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.
diff --git a/src/test/ui/specialization/min_specialization/impl_specialization_trait.rs b/src/test/ui/specialization/min_specialization/impl_specialization_trait.rs
new file mode 100644
index 000000000..723ed71c3
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/impl_specialization_trait.rs
@@ -0,0 +1,16 @@
+// Check that specialization traits can't be implemented without a feature.
+
+// gate-test-min_specialization
+
+// aux-build:specialization-trait.rs
+
+extern crate specialization_trait;
+
+struct A {}
+
+impl specialization_trait::SpecTrait for A {
+    //~^ ERROR implementing `rustc_specialization_trait` traits is unstable
+    fn method(&self) {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/impl_specialization_trait.stderr b/src/test/ui/specialization/min_specialization/impl_specialization_trait.stderr
new file mode 100644
index 000000000..934103d49
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/impl_specialization_trait.stderr
@@ -0,0 +1,10 @@
+error: implementing `rustc_specialization_trait` traits is unstable
+  --> $DIR/impl_specialization_trait.rs:11:1
+   |
+LL | impl specialization_trait::SpecTrait for A {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(min_specialization)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/implcit-well-formed-bounds.rs b/src/test/ui/specialization/min_specialization/implcit-well-formed-bounds.rs
new file mode 100644
index 000000000..98d7f9194
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/implcit-well-formed-bounds.rs
@@ -0,0 +1,30 @@
+// Test that specializing on the well-formed predicates of the trait and
+// self-type of an impl is allowed.
+
+// check-pass
+
+#![feature(min_specialization)]
+
+struct OrdOnly<T: Ord>(T);
+
+trait SpecTrait<U> {
+    fn f();
+}
+
+impl<T, U> SpecTrait<U> for T {
+    default fn f() {}
+}
+
+impl<T: Ord> SpecTrait<()> for OrdOnly<T> {
+    fn f() {}
+}
+
+impl<T: Ord> SpecTrait<OrdOnly<T>> for () {
+    fn f() {}
+}
+
+impl<T: Ord, U: Ord, V: Ord> SpecTrait<(OrdOnly<T>, OrdOnly<U>)> for &[OrdOnly<V>] {
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/issue-79224.rs b/src/test/ui/specialization/min_specialization/issue-79224.rs
new file mode 100644
index 000000000..408732fe9
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/issue-79224.rs
@@ -0,0 +1,24 @@
+#![feature(min_specialization)]
+use std::fmt::{self, Display};
+
+pub enum Cow<'a, B: ?Sized + 'a, O = <B as ToOwned>::Owned>
+where
+    B: ToOwned,
+{
+    Borrowed(&'a B),
+    Owned(O),
+}
+
+impl ToString for Cow<'_, str> {
+    fn to_string(&self) -> String {
+        String::new()
+    }
+}
+
+impl<B: ?Sized> Display for Cow<'_, B> { //~ ERROR: the trait bound `B: Clone` is not satisfied [E0277]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { //~ ERROR: the trait bound `B: Clone` is not satisfied [E0277]
+        write!(f, "foo")
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/issue-79224.stderr b/src/test/ui/specialization/min_specialization/issue-79224.stderr
new file mode 100644
index 000000000..cfb9007c7
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/issue-79224.stderr
@@ -0,0 +1,27 @@
+error[E0277]: the trait bound `B: Clone` is not satisfied
+  --> $DIR/issue-79224.rs:18:17
+   |
+LL | impl<B: ?Sized> Display for Cow<'_, B> {
+   |                 ^^^^^^^ the trait `Clone` is not implemented for `B`
+   |
+   = note: required because of the requirements on the impl of `ToOwned` for `B`
+help: consider further restricting this bound
+   |
+LL | impl<B: ?Sized + std::clone::Clone> Display for Cow<'_, B> {
+   |                +++++++++++++++++++
+
+error[E0277]: the trait bound `B: Clone` is not satisfied
+  --> $DIR/issue-79224.rs:19:12
+   |
+LL |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+   |            ^^^^^ the trait `Clone` is not implemented for `B`
+   |
+   = note: required because of the requirements on the impl of `ToOwned` for `B`
+help: consider further restricting this bound
+   |
+LL | impl<B: ?Sized + std::clone::Clone> Display for Cow<'_, B> {
+   |                +++++++++++++++++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/specialization/min_specialization/repeated_projection_type.rs b/src/test/ui/specialization/min_specialization/repeated_projection_type.rs
new file mode 100644
index 000000000..f21f39f06
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeated_projection_type.rs
@@ -0,0 +1,24 @@
+// Test that projection bounds can't be specialized on.
+
+#![feature(min_specialization)]
+
+trait X {
+    fn f();
+}
+trait Id {
+    type This;
+}
+impl<T> Id for T {
+    type This = T;
+}
+
+impl<T: Id> X for T {
+    default fn f() {}
+}
+
+impl<I, V: Id<This = (I,)>> X for V {
+    //~^ ERROR cannot specialize on
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/repeated_projection_type.stderr b/src/test/ui/specialization/min_specialization/repeated_projection_type.stderr
new file mode 100644
index 000000000..a751ba793
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeated_projection_type.stderr
@@ -0,0 +1,8 @@
+error: cannot specialize on associated type `<V as Id>::This == (I,)`
+  --> $DIR/repeated_projection_type.rs:19:15
+   |
+LL | impl<I, V: Id<This = (I,)>> X for V {
+   |               ^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/repeating_lifetimes.rs b/src/test/ui/specialization/min_specialization/repeating_lifetimes.rs
new file mode 100644
index 000000000..49bfacec0
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeating_lifetimes.rs
@@ -0,0 +1,19 @@
+// Test that directly specializing on repeated lifetime parameters is not
+// allowed.
+
+#![feature(min_specialization)]
+
+trait X {
+    fn f();
+}
+
+impl<T> X for T {
+    default fn f() {}
+}
+
+impl<'a> X for (&'a u8, &'a u8) {
+    //~^ ERROR specializing impl repeats parameter `'a`
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/repeating_lifetimes.stderr b/src/test/ui/specialization/min_specialization/repeating_lifetimes.stderr
new file mode 100644
index 000000000..16dccb10b
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeating_lifetimes.stderr
@@ -0,0 +1,8 @@
+error: specializing impl repeats parameter `'a`
+  --> $DIR/repeating_lifetimes.rs:14:1
+   |
+LL | impl<'a> X for (&'a u8, &'a u8) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/repeating_param.rs b/src/test/ui/specialization/min_specialization/repeating_param.rs
new file mode 100644
index 000000000..5a1c97fd3
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeating_param.rs
@@ -0,0 +1,17 @@
+// Test that specializing on two type parameters being equal is not allowed.
+
+#![feature(min_specialization)]
+
+trait X {
+    fn f();
+}
+
+impl<T> X for T {
+    default fn f() {}
+}
+impl<T> X for (T, T) {
+    //~^ ERROR specializing impl repeats parameter `T`
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/repeating_param.stderr b/src/test/ui/specialization/min_specialization/repeating_param.stderr
new file mode 100644
index 000000000..5e6adf723
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/repeating_param.stderr
@@ -0,0 +1,8 @@
+error: specializing impl repeats parameter `T`
+  --> $DIR/repeating_param.rs:12:1
+   |
+LL | impl<T> X for (T, T) {
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/spec-iter.rs b/src/test/ui/specialization/min_specialization/spec-iter.rs
new file mode 100644
index 000000000..e17e9dd5f
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/spec-iter.rs
@@ -0,0 +1,20 @@
+// Check that we can specialize on a concrete iterator type. This requires us
+// to consider which parameters in the parent impl are constrained.
+
+// check-pass
+
+#![feature(min_specialization)]
+
+trait SpecFromIter<T> {
+    fn f(&self);
+}
+
+impl<'a, T: 'a, I: Iterator<Item = &'a T>> SpecFromIter<T> for I {
+    default fn f(&self) {}
+}
+
+impl<'a, T> SpecFromIter<T> for std::slice::Iter<'a, T> {
+    fn f(&self) {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/spec-marker-supertraits.rs b/src/test/ui/specialization/min_specialization/spec-marker-supertraits.rs
new file mode 100644
index 000000000..3bb2480e9
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/spec-marker-supertraits.rs
@@ -0,0 +1,29 @@
+// Check that supertraits cannot be used to work around min_specialization
+// limitations.
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+trait HasMethod {
+    fn method(&self);
+}
+
+#[rustc_unsafe_specialization_marker]
+trait Marker: HasMethod {}
+
+trait Spec {
+    fn spec_me(&self);
+}
+
+impl<T> Spec for T {
+    default fn spec_me(&self) {}
+}
+
+impl<T: Marker> Spec for T {
+    //~^ ERROR cannot specialize on trait `HasMethod`
+    fn spec_me(&self) {
+        self.method();
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/spec-marker-supertraits.stderr b/src/test/ui/specialization/min_specialization/spec-marker-supertraits.stderr
new file mode 100644
index 000000000..ba9d6bbe3
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/spec-marker-supertraits.stderr
@@ -0,0 +1,8 @@
+error: cannot specialize on trait `HasMethod`
+  --> $DIR/spec-marker-supertraits.rs:22:9
+   |
+LL | impl<T: Marker> Spec for T {
+   |         ^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/spec-reference.rs b/src/test/ui/specialization/min_specialization/spec-reference.rs
new file mode 100644
index 000000000..377889e2c
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/spec-reference.rs
@@ -0,0 +1,19 @@
+// Check that lifetime parameters are allowed in specializing impls.
+
+// check-pass
+
+#![feature(min_specialization)]
+
+trait MySpecTrait {
+    fn f();
+}
+
+impl<T> MySpecTrait for T {
+    default fn f() {}
+}
+
+impl<'a, T: ?Sized> MySpecTrait for &'a T {
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialization_marker.rs b/src/test/ui/specialization/min_specialization/specialization_marker.rs
new file mode 100644
index 000000000..93462d02e
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_marker.rs
@@ -0,0 +1,17 @@
+// Test that `rustc_unsafe_specialization_marker` is only allowed on marker traits.
+
+#![feature(rustc_attrs)]
+
+#[rustc_unsafe_specialization_marker]
+trait SpecMarker {
+    fn f();
+    //~^ ERROR marker traits
+}
+
+#[rustc_unsafe_specialization_marker]
+trait SpecMarker2 {
+    type X;
+    //~^ ERROR marker traits
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialization_marker.stderr b/src/test/ui/specialization/min_specialization/specialization_marker.stderr
new file mode 100644
index 000000000..b47c14f3c
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_marker.stderr
@@ -0,0 +1,15 @@
+error[E0714]: marker traits cannot have associated items
+  --> $DIR/specialization_marker.rs:7:5
+   |
+LL |     fn f();
+   |     ^^^^^^^
+
+error[E0714]: marker traits cannot have associated items
+  --> $DIR/specialization_marker.rs:13:5
+   |
+LL |     type X;
+   |     ^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0714`.
diff --git a/src/test/ui/specialization/min_specialization/specialization_super_trait.rs b/src/test/ui/specialization/min_specialization/specialization_super_trait.rs
new file mode 100644
index 000000000..145f376ed
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_super_trait.rs
@@ -0,0 +1,18 @@
+// Test that supertraits can't be assumed in impls of
+// `rustc_specialization_trait`, as such impls would
+// allow specializing on the supertrait.
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+#[rustc_specialization_trait]
+trait SpecMarker: Default {
+    fn f();
+}
+
+impl<T: Default> SpecMarker for T {
+    //~^ ERROR cannot specialize
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialization_super_trait.stderr b/src/test/ui/specialization/min_specialization/specialization_super_trait.stderr
new file mode 100644
index 000000000..e93578662
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_super_trait.stderr
@@ -0,0 +1,8 @@
+error: cannot specialize on trait `Default`
+  --> $DIR/specialization_super_trait.rs:13:9
+   |
+LL | impl<T: Default> SpecMarker for T {
+   |         ^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/specialization_trait.rs b/src/test/ui/specialization/min_specialization/specialization_trait.rs
new file mode 100644
index 000000000..d597278d2
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_trait.rs
@@ -0,0 +1,26 @@
+// Test that `rustc_specialization_trait` requires always applicable impls.
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+#[rustc_specialization_trait]
+trait SpecMarker {
+    fn f();
+}
+
+impl SpecMarker for &'static u8 {
+    //~^ ERROR cannot specialize
+    fn f() {}
+}
+
+impl<T> SpecMarker for (T, T) {
+    //~^ ERROR specializing impl
+    fn f() {}
+}
+
+impl<T: Clone> SpecMarker for [T] {
+    //~^ ERROR cannot specialize
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialization_trait.stderr b/src/test/ui/specialization/min_specialization/specialization_trait.stderr
new file mode 100644
index 000000000..bc87ae0f8
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialization_trait.stderr
@@ -0,0 +1,20 @@
+error: cannot specialize on `'static` lifetime
+  --> $DIR/specialization_trait.rs:11:1
+   |
+LL | impl SpecMarker for &'static u8 {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: specializing impl repeats parameter `T`
+  --> $DIR/specialization_trait.rs:16:1
+   |
+LL | impl<T> SpecMarker for (T, T) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: cannot specialize on trait `Clone`
+  --> $DIR/specialization_trait.rs:21:9
+   |
+LL | impl<T: Clone> SpecMarker for [T] {
+   |         ^^^^^
+
+error: aborting due to 3 previous errors
+
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_marker.rs b/src/test/ui/specialization/min_specialization/specialize_on_marker.rs
new file mode 100644
index 000000000..4219bd13b
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_marker.rs
@@ -0,0 +1,24 @@
+// Test that specializing on a `rustc_unsafe_specialization_marker` trait is
+// allowed.
+
+// check-pass
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+#[rustc_unsafe_specialization_marker]
+trait SpecMarker {}
+
+trait X {
+    fn f();
+}
+
+impl<T> X for T {
+    default fn f() {}
+}
+
+impl<T: SpecMarker> X for T {
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_spec_trait.rs b/src/test/ui/specialization/min_specialization/specialize_on_spec_trait.rs
new file mode 100644
index 000000000..abbab5c23
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_spec_trait.rs
@@ -0,0 +1,27 @@
+// Test that specializing on a `rustc_specialization_trait` trait is allowed.
+
+// check-pass
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+#[rustc_specialization_trait]
+trait SpecTrait {
+    fn g(&self);
+}
+
+trait X {
+    fn f(&self);
+}
+
+impl<T> X for T {
+    default fn f(&self) {}
+}
+
+impl<T: SpecTrait> X for T {
+    fn f(&self) {
+        self.g();
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_static.rs b/src/test/ui/specialization/min_specialization/specialize_on_static.rs
new file mode 100644
index 000000000..dd1b05401
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_static.rs
@@ -0,0 +1,18 @@
+// Test that directly specializing on `'static` is not allowed.
+
+#![feature(min_specialization)]
+
+trait X {
+    fn f();
+}
+
+impl<T> X for &'_ T {
+    default fn f() {}
+}
+
+impl X for &'static u8 {
+    //~^ ERROR cannot specialize on `'static` lifetime
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_static.stderr b/src/test/ui/specialization/min_specialization/specialize_on_static.stderr
new file mode 100644
index 000000000..9a16798f1
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_static.stderr
@@ -0,0 +1,8 @@
+error: cannot specialize on `'static` lifetime
+  --> $DIR/specialize_on_static.rs:13:1
+   |
+LL | impl X for &'static u8 {
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_trait.rs b/src/test/ui/specialization/min_specialization/specialize_on_trait.rs
new file mode 100644
index 000000000..0588442c3
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_trait.rs
@@ -0,0 +1,20 @@
+// Test that specializing on a trait is not allowed in general.
+
+#![feature(min_specialization)]
+
+trait SpecMarker {}
+
+trait X {
+    fn f();
+}
+
+impl<T> X for T {
+    default fn f() {}
+}
+
+impl<T: SpecMarker> X for T {
+    //~^ ERROR cannot specialize on trait `SpecMarker`
+    fn f() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/specialization/min_specialization/specialize_on_trait.stderr b/src/test/ui/specialization/min_specialization/specialize_on_trait.stderr
new file mode 100644
index 000000000..7b79c7eb4
--- /dev/null
+++ b/src/test/ui/specialization/min_specialization/specialize_on_trait.stderr
@@ -0,0 +1,8 @@
+error: cannot specialize on trait `SpecMarker`
+  --> $DIR/specialize_on_trait.rs:15:9
+   |
+LL | impl<T: SpecMarker> X for T {
+   |         ^^^^^^^^^^
+
+error: aborting due to previous error
+
-- 
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