Use erased self type when autoderefing for trait error suggestion

Author: compiler-errors

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

@@ -776,18 +776,14 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 real_trait_pred = parent_trait_pred;
             }
 
-            let real_ty = real_trait_pred.self_ty();
             // We `erase_late_bound_regions` here because `make_subregion` does not handle
             // `ReLateBound`, and we don't particularly care about the regions.
-            if !self.can_eq(
-                obligation.param_env,
-                self.tcx.erase_late_bound_regions(real_ty),
-                arg_ty,
-            ) {
+            let real_ty = self.tcx.erase_late_bound_regions(real_trait_pred.self_ty());
+            if !self.can_eq(obligation.param_env, real_ty, arg_ty) {
                 continue;
             }
 
-            if let ty::Ref(region, base_ty, mutbl) = *real_ty.skip_binder().kind() {
+            if let ty::Ref(region, base_ty, mutbl) = *real_ty.kind() {
                 let autoderef = (self.autoderef_steps)(base_ty);
                 if let Some(steps) =
                     autoderef.into_iter().enumerate().find_map(|(steps, (ty, obligations))| {

tests/ui/traits/dont-autoderef-ty-with-escaping-var.rs

@@ -0,0 +1,22 @@
+// issue:113951
+
+trait Foo<'x, T> {}
+
+trait RefFoo<T> {
+    fn ref_foo(&self);
+}
+
+impl<T> RefFoo<T> for T
+where
+    for<'a> &'a mut Vec<&'a u32>: Foo<'static, T>,
+{
+    fn ref_foo(&self) {}
+}
+
+fn coerce_lifetime2() {
+    <i32 as RefFoo<i32>>::ref_foo(unknown);
+    //~^ ERROR cannot find value `unknown` in this scope
+    //~| ERROR the trait bound `for<'a> &'a mut Vec<&'a u32>: Foo<'static, i32>` is not satisfied
+}
+
+fn main() {}

tests/ui/traits/dont-autoderef-ty-with-escaping-var.stderr

@@ -0,0 +1,27 @@
+error[E0425]: cannot find value `unknown` in this scope
+  --> $DIR/dont-autoderef-ty-with-escaping-var.rs:17:35
+   |
+LL |     <i32 as RefFoo<i32>>::ref_foo(unknown);
+   |                                   ^^^^^^^ not found in this scope
+
+error[E0277]: the trait bound `for<'a> &'a mut Vec<&'a u32>: Foo<'static, i32>` is not satisfied
+  --> $DIR/dont-autoderef-ty-with-escaping-var.rs:17:35
+   |
+LL |     <i32 as RefFoo<i32>>::ref_foo(unknown);
+   |     ----------------------------- ^^^^^^^ the trait `for<'a> Foo<'static, i32>` is not implemented for `&'a mut Vec<&'a u32>`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required for `i32` to implement `RefFoo<i32>`
+  --> $DIR/dont-autoderef-ty-with-escaping-var.rs:9:9
+   |
+LL | impl<T> RefFoo<T> for T
+   |         ^^^^^^^^^     ^
+LL | where
+LL |     for<'a> &'a mut Vec<&'a u32>: Foo<'static, T>,
+   |                                   --------------- unsatisfied trait bound introduced here
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0425.
+For more information about an error, try `rustc --explain E0277`.