Add a test showing how impl_trait_in_bindings is a breaking change

Author: oli-obk

src/test/ui/mir/issue-75053.full_tait.stderr

@@ -0,0 +1,17 @@
+warning: the feature `type_alias_impl_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-75053.rs:5:32
+   |
+LL | #![cfg_attr(full_tait, feature(type_alias_impl_trait))]
+   |                                ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+
+error: fatal error triggered by #[rustc_error]
+  --> $DIR/issue-75053.rs:51:1
+   |
+LL | fn main() {
+   | ^^^^^^^^^
+
+error: aborting due to previous error; 1 warning emitted
+

src/test/ui/mir/issue-75053.in_bindings.stderr

@@ -0,0 +1,24 @@
+warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-75053.rs:7:34
+   |
+LL | #![cfg_attr(in_bindings, 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[E0282]: type annotations needed
+  --> $DIR/issue-75053.rs:53:38
+   |
+LL |     type O;
+   |     ------- `<Self as MyIndex<T>>::O` defined here
+...
+LL |     let _pos: Phantom1<DummyT<()>> = Scope::new().my_index();
+   |                                      ^^^^^^^^^^-------------
+   |                                      |
+   |                                      this method call resolves to `<Self as MyIndex<T>>::O`
+   |                                      cannot infer type for type parameter `T`
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/mir/issue-75053.min_tait.stderr

@@ -0,0 +1,8 @@
+error: fatal error triggered by #[rustc_error]
+  --> $DIR/issue-75053.rs:51:1
+   |
+LL | fn main() {
+   | ^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/mir/issue-75053.rs

@@ -1,7 +1,11 @@
 // compile-flags: -Z mir-opt-level=3
-// build-pass
 
-#![feature(type_alias_impl_trait)]
+// revisions: min_tait full_tait in_bindings
+#![feature(min_type_alias_impl_trait, rustc_attrs)]
+#![cfg_attr(full_tait, feature(type_alias_impl_trait))]
+//[full_tait]~^ WARN incomplete
+#![cfg_attr(in_bindings, feature(impl_trait_in_bindings))]
+//[in_bindings]~^ WARN incomplete
 
 use std::marker::PhantomData;
 
@@ -43,6 +47,9 @@ impl<T: MyFrom<Phantom2<DummyT<U>>>, U> MyIndex<Phantom1<T>> for Scope<U> {
     }
 }
 
+#[rustc_error]
 fn main() {
+    //[min_tait,full_tait]~^ ERROR rustc_error
     let _pos: Phantom1<DummyT<()>> = Scope::new().my_index();
+    //[in_bindings]~^ ERROR type annotations needed
 }