Rollup merge of #72045 - RalfJung:incomplete-unsound, r=petrochenkov

Incomplete features can also be unsound

Some incomplete features do not just ICE, they are also currently unsound (e.g. https://github.com/rust-lang/rust/pull/72029, and also `specialization` -- which is not yet marked incomplete but [should be](https://github.com/rust-lang/rust/pull/71420)). This makes the message reflect that.

While at it I also added a link to the tracking issue, which hopefully should explain what is incomplete/unsound about the feature.

6 files changed, 10 insertions, 6 deletions

diff --git a/src/test/ui/impl-trait/bindings-opaque.rs b/src/test/ui/impl-trait/bindings-opaque.rs
index d4eef29ed32..d1f42be077d 100644
--- a/src/test/ui/impl-trait/bindings-opaque.rs
+++ b/src/test/ui/impl-trait/bindings-opaque.rs
@@ -1,5 +1,5 @@
 #![feature(impl_trait_in_bindings)]
-//~^ WARN the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+//~^ WARN the feature `impl_trait_in_bindings` is incomplete
 
 const FOO: impl Copy = 42;
 
diff --git a/src/test/ui/impl-trait/bindings-opaque.stderr b/src/test/ui/impl-trait/bindings-opaque.stderr
index 14d33270ca5..6656968d79a 100644
--- a/src/test/ui/impl-trait/bindings-opaque.stderr
+++ b/src/test/ui/impl-trait/bindings-opaque.stderr
@@ -1,10 +1,11 @@
-warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/bindings-opaque.rs:1:12
    |
 LL | #![feature(impl_trait_in_bindings)]
    |            ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
 
 error[E0599]: no method named `count_ones` found for opaque type `impl std::marker::Copy` in the current scope
   --> $DIR/bindings-opaque.rs:11:17
diff --git a/src/test/ui/impl-trait/bindings.rs b/src/test/ui/impl-trait/bindings.rs
index 104a44d6566..fd79ba68fbd 100644
--- a/src/test/ui/impl-trait/bindings.rs
+++ b/src/test/ui/impl-trait/bindings.rs
@@ -1,5 +1,5 @@
 #![feature(impl_trait_in_bindings)]
-//~^ WARN the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+//~^ WARN the feature `impl_trait_in_bindings` is incomplete
 
 fn a<T: Clone>(x: T) {
     const foo: impl Clone = x;
diff --git a/src/test/ui/impl-trait/bindings.stderr b/src/test/ui/impl-trait/bindings.stderr
index 7d64980074a..e983fdecdba 100644
--- a/src/test/ui/impl-trait/bindings.stderr
+++ b/src/test/ui/impl-trait/bindings.stderr
@@ -22,13 +22,14 @@ error[E0435]: attempt to use a non-constant value in a constant
 LL |         const foo: impl Clone = x;
    |                                 ^ non-constant value
 
-warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/bindings.rs:1:12
    |
 LL | #![feature(impl_trait_in_bindings)]
    |            ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
 
 error: aborting due to 4 previous errors; 1 warning emitted
 
diff --git a/src/test/ui/impl-trait/bound-normalization-fail.stderr b/src/test/ui/impl-trait/bound-normalization-fail.stderr
index f5092044627..36b4ebca4df 100644
--- a/src/test/ui/impl-trait/bound-normalization-fail.stderr
+++ b/src/test/ui/impl-trait/bound-normalization-fail.stderr
@@ -1,10 +1,11 @@
-warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/bound-normalization-fail.rs:4:12
    |
 LL | #![feature(impl_trait_in_bindings)]
    |            ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
 
 error[E0271]: type mismatch resolving `<Foo<()> as FooLike>::Output == <T as impl_trait::Trait>::Assoc`
   --> $DIR/bound-normalization-fail.rs:27:32
diff --git a/src/test/ui/impl-trait/bound-normalization-pass.stderr b/src/test/ui/impl-trait/bound-normalization-pass.stderr
index fcc3cc51236..afc181a906a 100644
--- a/src/test/ui/impl-trait/bound-normalization-pass.stderr
+++ b/src/test/ui/impl-trait/bound-normalization-pass.stderr
@@ -1,10 +1,11 @@
-warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash
+warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/bound-normalization-pass.rs:5:12
    |
 LL | #![feature(impl_trait_in_bindings)]
    |            ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
 
 warning: 1 warning emitted