Fix debug assert failure in note_obligation_cause_code_inner

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

@@ -4974,8 +4974,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         .as_ref()
                         .and_then(|typeck| typeck.node_type_opt(expr.hir_id))
                     && let Some(pred) = predicate.as_clause()
-                    && let ty::ClauseKind::Trait(pred) = pred.kind().skip_binder()
-                    && self.can_eq(param_env, pred.self_ty(), expr_ty)
+                    && let Some(pred) = pred.as_trait_clause()
+                    && self
+                        .infcx
+                        .enter_forall(pred, |pred| self.can_eq(param_env, pred.self_ty(), expr_ty))
                 {
                     (expr_ty, expr)
                 } else {

tests/ui/impl-trait/diagnostics/incorrect-skip-binder-for-item-bound.next.stderr

@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `for<'a> u8: From<&'a ()>` is not satisfied
-  --> $DIR/incorrect-skip-binder-for-item-bound.rs:19:15
+  --> $DIR/incorrect-skip-binder-for-item-bound.rs:16:15
    |
 LL | fn hello() -> impl for<'a> A<'a, Assoc: Into<u8> + 'static + Copy> {
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> From<&'a ()>` is not implemented for `u8`

tests/ui/impl-trait/diagnostics/incorrect-skip-binder-for-item-bound.old.stderr

@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `for<'a> u8: From<&'a ()>` is not satisfied
+  --> $DIR/incorrect-skip-binder-for-item-bound.rs:16:15
+   |
+LL | fn hello() -> impl for<'a> A<'a, Assoc: Into<u8> + 'static + Copy> {
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> From<&'a ()>` is not implemented for `u8`
+   |
+help: `u8` implements trait `From<T>`
+  --> $SRC_DIR/core/src/convert/num.rs:LL:COL
+   |
+   = note: `From<bool>`
+  ::: $SRC_DIR/core/src/convert/num.rs:LL:COL
+   |
+   = note: in this macro invocation
+  --> $SRC_DIR/core/src/ascii/ascii_char.rs:LL:COL
+   |
+   = note: `From<std::ascii::Char>`
+  ::: $SRC_DIR/core/src/ascii/ascii_char.rs:LL:COL
+   |
+   = note: in this macro invocation
+   = note: required for `&'a ()` to implement `for<'a> Into<u8>`
+   = note: this error originates in the macro `impl_from_bool` which comes from the expansion of the macro `into_int_impl` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/diagnostics/incorrect-skip-binder-for-item-bound.rs

@@ -1,9 +1,6 @@
 //@ revisions: old next
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
-//@[old] failure-status: 101
-//@[old] dont-check-compiler-stderr
-//@[old] known-bug: #139381
 //@ needs-rustc-debug-assertions
 
 // An ICE caused by an incorrect `skip_binder()` in diagnostics code, see #139381.
@@ -17,7 +14,7 @@ impl<'a> A<'a> for () {
 }
 
 fn hello() -> impl for<'a> A<'a, Assoc: Into<u8> + 'static + Copy> {
-    //[next]~^ ERROR: the trait bound `for<'a> u8: From<&'a ()>` is not satisfied
+    //~^ ERROR: the trait bound `for<'a> u8: From<&'a ()>` is not satisfied
     ()
 }