Do not ICE on unmet trait alias impl bounds

Author: eggyal

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -714,7 +714,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         );
                     }
                     Some(Node::Item(hir::Item {
-                        ident, kind: hir::ItemKind::Trait(..), ..
+                        ident,
+                        kind: hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..),
+                        ..
                     })) => {
                         skip_list.insert(p);
                         let entry = spanned_predicates.entry(ident.span);

tests/ui/traits/alias/issue-108132-unmet-trait-alias-bound-on-generic-impl.rs

@@ -0,0 +1,15 @@
+// Regression test for #108132: do not ICE upon unmet trait alias constraint in generic impl
+
+#![feature(trait_alias)]
+
+trait IteratorAlias = Iterator;
+
+struct Foo<I>(I);
+
+impl<I: IteratorAlias> Foo<I> {
+    fn f() {}
+}
+
+fn main() {
+    Foo::<()>::f() //~ trait bounds were not satisfied
+}

tests/ui/traits/alias/issue-108132-unmet-trait-alias-bound-on-generic-impl.stderr

@@ -0,0 +1,25 @@
+error[E0599]: the function or associated item `f` exists for struct `Foo<()>`, but its trait bounds were not satisfied
+  --> $DIR/issue-108132-unmet-trait-alias-bound-on-generic-impl.rs:14:16
+   |
+LL | struct Foo<I>(I);
+   | ------------- function or associated item `f` not found for this struct
+...
+LL |     Foo::<()>::f()
+   |                ^ function or associated item cannot be called on `Foo<()>` due to unsatisfied trait bounds
+   |
+note: trait bound `(): Iterator` was not satisfied
+  --> $DIR/issue-108132-unmet-trait-alias-bound-on-generic-impl.rs:5:23
+   |
+LL | trait IteratorAlias = Iterator;
+   |       -------------   ^^^^^^^^ unsatisfied trait bound introduced here
+note: trait bound `(): IteratorAlias` was not satisfied
+  --> $DIR/issue-108132-unmet-trait-alias-bound-on-generic-impl.rs:9:9
+   |
+LL | impl<I: IteratorAlias> Foo<I> {
+   |         ^^^^^^^^^^^^^  ------
+   |         |
+   |         unsatisfied trait bound introduced here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.