Rollup merge of #96679 - ricked-twice:issue-96223-fix, r=jackh726

Quick fix for #96223.

This PR is a quick fix regarding #96223.

As mentioned in the issue, others modification could be added to not elide types with bound vars from suggestions.

Special thanks to `@jackh726` for mentoring and `@Manishearth` for minimal test case.

r? `@jackh726`

Author: JohnTitor

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -866,7 +866,13 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 return false;
             }
 
-            let orig_ty = old_pred.self_ty().skip_binder();
+            // This is a quick fix to resolve an ICE (#96223).
+            // This change should probably be deeper.
+            // As suggested by @jackh726, `mk_trait_obligation_with_new_self_ty` could take a `Binder<(TraitRef, Ty)>
+            // instead of `Binder<Ty>` leading to some changes to its call places.
+            let Some(orig_ty) = old_pred.self_ty().no_bound_vars() else {
+                return false;
+            };
             let mk_result = |new_ty| {
                 let obligation =
                     self.mk_trait_obligation_with_new_self_ty(param_env, old_pred, new_ty);

src/test/ui/suggestions/issue-96223.rs

@@ -0,0 +1,52 @@
+// Previously ICEd because we didn't properly track binders in suggestions
+// check-fail
+
+pub trait Foo<'de>: Sized {}
+
+pub trait Bar<'a>: 'static {
+    type Inner: 'a;
+}
+
+pub trait Fubar {
+    type Bar: for<'a> Bar<'a>;
+}
+
+pub struct Baz<T>(pub T);
+
+impl<'de, T> Foo<'de> for Baz<T> where T: Foo<'de> {}
+
+struct Empty;
+
+impl<M> Dummy<M> for Empty
+where
+    M: Fubar,
+    for<'de> Baz<<M::Bar as Bar<'de>>::Inner>: Foo<'de>,
+{
+}
+
+pub trait Dummy<M>
+where
+    M: Fubar,
+{
+}
+
+pub struct EmptyBis<'a>(&'a [u8]);
+
+impl<'a> Bar<'a> for EmptyBis<'static> {
+    type Inner = EmptyBis<'a>;
+}
+
+pub struct EmptyMarker;
+
+impl Fubar for EmptyMarker {
+    type Bar = EmptyBis<'static>;
+}
+
+fn icey_bounds<D: Dummy<EmptyMarker>>(p: &D) {}
+
+fn trigger_ice() {
+    let p = Empty;
+    icey_bounds(&p); //~ERROR the trait bound
+}
+
+fn main() {}

src/test/ui/suggestions/issue-96223.stderr

@@ -0,0 +1,28 @@
+error[E0277]: the trait bound `for<'de> EmptyBis<'de>: Foo<'_>` is not satisfied
+  --> $DIR/issue-96223.rs:49:17
+   |
+LL |     icey_bounds(&p);
+   |     ----------- ^^ the trait `for<'de> Foo<'_>` is not implemented for `EmptyBis<'de>`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the trait `Foo<'de>` is implemented for `Baz<T>`
+note: required because of the requirements on the impl of `for<'de> Foo<'de>` for `Baz<EmptyBis<'de>>`
+  --> $DIR/issue-96223.rs:16:14
+   |
+LL | impl<'de, T> Foo<'de> for Baz<T> where T: Foo<'de> {}
+   |              ^^^^^^^^     ^^^^^^
+note: required because of the requirements on the impl of `Dummy<EmptyMarker>` for `Empty`
+  --> $DIR/issue-96223.rs:20:9
+   |
+LL | impl<M> Dummy<M> for Empty
+   |         ^^^^^^^^     ^^^^^
+note: required by a bound in `icey_bounds`
+  --> $DIR/issue-96223.rs:45:19
+   |
+LL | fn icey_bounds<D: Dummy<EmptyMarker>>(p: &D) {}
+   |                   ^^^^^^^^^^^^^^^^^^ required by this bound in `icey_bounds`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.