Merge pull request #22930 from shulaoda/07-27-fix_don_t_panic_on_a_qualified_path_whose_trait_is_not_a_trait

fix: don't panic on a qualified path whose trait is not a trait

Author: ChayimFriedman2

crates/hir-ty/src/lower/path.rs

@@ -1234,6 +1234,12 @@ pub(crate) fn substs_from_args_and_bindings<'db>(
         };
         params.next();
         substs.push(self_ty);
+    } else if has_self_arg {
+        // A qualified path `<T as Trait>::Assoc` where `Trait` resolved to something without a
+        // `Self` parameter, e.g. a struct. `check_generic_args_len()` skips the self type
+        // unconditionally, so drop it here too instead of matching it against a real parameter.
+        // FIXME: Report a diagnostic here, rustc emits `E0404: expected trait, found struct`.
+        args.next();
     }
 
     loop {

crates/hir-ty/src/tests/regression.rs

@@ -3016,3 +3016,15 @@ fn f(s: S) { s.m(); }
     "#,
     );
 }
+
+#[test]
+fn regression_22799() {
+    check_no_mismatches(
+        r#"
+struct S;
+fn f() {
+    <S as S>::S;
+}
+    "#,
+    );
+}