Require `~const` qualifier on trait bounds in specializing impls if present in base impl.

7 files changed, 94 insertions, 8 deletions

diff --git a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.rs b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.rs
new file mode 100644
index 00000000000..3ac90992486
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.rs
@@ -0,0 +1,46 @@
+// Tests that trait bounds on specializing trait impls must be `~const` if the
+// same bound is present on the default impl and is `~const` there.
+
+#![feature(const_trait_impl)]
+#![feature(rustc_attrs)]
+#![feature(min_specialization)]
+
+#[rustc_specialization_trait]
+trait Specialize {}
+
+#[const_trait]
+trait Foo {}
+
+#[const_trait]
+trait Bar {}
+
+// bgr360: I was only able to exercise the code path that raises the
+// "missing ~const qualifier" error by making this base impl non-const, even
+// though that doesn't really make sense to do. As seen below, if the base impl
+// is made const, rustc fails earlier with an overlapping impl failure.
+impl<T> Bar for T
+where
+    T: ~const Foo,
+{}
+
+impl<T> Bar for T
+where
+    T: Foo, //~ ERROR missing `~const` qualifier
+    T: Specialize,
+{}
+
+#[const_trait]
+trait Baz {}
+
+impl<T> const Baz for T
+where
+    T: ~const Foo,
+{}
+
+impl<T> const Baz for T //~ ERROR conflicting implementations of trait `Baz`
+where
+    T: Foo,
+    T: Specialize,
+{}
+
+fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.stderr b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.stderr
new file mode 100644
index 00000000000..583c4cec77f
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-bound-non-const-specialized-bound.stderr
@@ -0,0 +1,18 @@
+error: missing `~const` qualifier
+  --> $DIR/const-default-bound-non-const-specialized-bound.rs:28:8
+   |
+LL |     T: Foo,
+   |        ^^^
+
+error[E0119]: conflicting implementations of trait `Baz`
+  --> $DIR/const-default-bound-non-const-specialized-bound.rs:40:1
+   |
+LL | impl<T> const Baz for T
+   | ----------------------- first implementation here
+...
+LL | impl<T> const Baz for T
+   | ^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0119`.
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-non-const-specialized.rs b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-impl-non-const-specialized-impl.rs
index 79dd4950af3..a3bb9b3f93e 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-non-const-specialized.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-impl-non-const-specialized-impl.rs
@@ -1,5 +1,4 @@
-// Tests that a const default trait impl cannot be specialized by a non-const
-// trait impl.
+// Tests that specializing trait impls must be at least as const as the default impl.
 
 #![feature(const_trait_impl)]
 #![feature(min_specialization)]
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-non-const-specialized.stderr b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-impl-non-const-specialized-impl.stderr
index 5232a8609cd..24766804708 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-non-const-specialized.stderr
+++ b/src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-impl-non-const-specialized-impl.stderr
@@ -1,5 +1,5 @@
 error: cannot specialize on const impl with non-const impl
-  --> $DIR/const-default-non-const-specialized.rs:20:1
+  --> $DIR/const-default-impl-non-const-specialized-impl.rs:19:1
    |
 LL | impl Value for FortyTwo {
    | ^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specialization/issue-95187-same-trait-bound-different-constness.rs b/src/test/ui/rfc-2632-const-trait-impl/specialization/issue-95187-same-trait-bound-different-constness.rs
index 3370aebf063..1e6b1c6513b 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/specialization/issue-95187-same-trait-bound-different-constness.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/specialization/issue-95187-same-trait-bound-different-constness.rs
@@ -1,5 +1,6 @@
-// Tests that `T: Foo` and `T: ~const Foo` are treated as equivalent for the
-// purposes of min_specialization.
+// Tests that `T: ~const Foo` in a specializing impl is treated as equivalent to
+// `T: Foo` in the default impl for the purposes of specialization (i.e., it
+// does not think that the user is attempting to specialize on trait `Foo`).
 
 // check-pass
 
@@ -27,4 +28,18 @@ where
     T: Specialize,
 {}
 
+#[const_trait]
+trait Baz {}
+
+impl<T> const Baz for T
+where
+    T: Foo,
+{}
+
+impl<T> const Baz for T
+where
+    T: ~const Foo,
+    T: Specialize,
+{}
+
 fn main() {}
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.rs b/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.rs
index ff0cd489d47..9ab170f0920 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.rs
+++ b/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.rs
@@ -17,7 +17,9 @@ impl<T: ~const Default> const A for T {
     }
 }
 
-impl<T: Default + Sup> A for T { //~ ERROR: cannot specialize
+impl<T: Default + Sup> A for T {
+//~^ ERROR: cannot specialize
+//~| ERROR: missing `~const` qualifier
     fn a() -> u32 {
         3
     }
diff --git a/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.stderr b/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.stderr
index 3296c109c4e..281ba82d644 100644
--- a/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.stderr
+++ b/src/test/ui/rfc-2632-const-trait-impl/specializing-constness.stderr
@@ -1,8 +1,14 @@
-error: cannot specialize on trait `Default`
+error: cannot specialize on const impl with non-const impl
+  --> $DIR/specializing-constness.rs:20:1
+   |
+LL | impl<T: Default + Sup> A for T {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: missing `~const` qualifier
   --> $DIR/specializing-constness.rs:20:9
    |
 LL | impl<T: Default + Sup> A for T {
    |         ^^^^^^^
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors