Rollup merge of rust-lang#66388 - estebank:melt-ice, r=Centril

Do not ICE on recovery from unmet associated type bound obligation

Fix rust-lang#66353.

r? @Centril

Author: JohnTitor

src/librustc_typeck/check/mod.rs

@@ -3108,7 +3108,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         fallback_has_occurred: bool,
         mutate_fullfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
     ) {
-        if let Err(mut errors) = self.fulfillment_cx.borrow_mut().select_where_possible(self) {
+        let result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
+        if let Err(mut errors) = result {
             mutate_fullfillment_errors(&mut errors);
             self.report_fulfillment_errors(&errors, self.inh.body_id, fallback_has_occurred);
         }

src/test/ui/issues/issue-66353.rs

@@ -0,0 +1,15 @@
+// #66353: ICE when trying to recover from incorrect associated type
+
+trait _Func<T> {
+    fn func(_: Self);
+}
+
+trait _A {
+    type AssocT;
+}
+
+fn main() {
+    _Func::< <() as _A>::AssocT >::func(());
+    //~^ ERROR the trait bound `(): _A` is not satisfied
+    //~| ERROR the trait bound `(): _Func<_>` is not satisfied
+}

src/test/ui/issues/issue-66353.stderr

@@ -0,0 +1,18 @@
+error[E0277]: the trait bound `(): _A` is not satisfied
+  --> $DIR/issue-66353.rs:12:14
+   |
+LL |     _Func::< <() as _A>::AssocT >::func(());
+   |              ^^^^^^^^^^^^^^^^^^ the trait `_A` is not implemented for `()`
+
+error[E0277]: the trait bound `(): _Func<_>` is not satisfied
+  --> $DIR/issue-66353.rs:12:41
+   |
+LL |     fn func(_: Self);
+   |     ----------------- required by `_Func::func`
+...
+LL |     _Func::< <() as _A>::AssocT >::func(());
+   |                                         ^^ the trait `_Func<_>` is not implemented for `()`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.