Rollup merge of rust-lang#156301 - TaKO8Ki:fix-156299-closure-receiver-suggestion-ice, r=wesleywiser

Avoid ICE when suggesting as_ref for ill-typed closure receivers

Fixes rust-lang#156299

When building mismatch suggestions, `can_use_as_ref` may inspect the receiver of a method call that is itself an ill-typed closure expression. In that recovery path, the receiver may not have a recorded type in `TypeckResults`.

Use `expr_ty_opt` instead of `expr_ty` so the optional `as_ref()` suggestion is skipped when the receiver type is unavailable.

Author: JonathanBrouwer

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -2787,7 +2787,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return None;
         };
 
-        let self_ty = self.typeck_results.borrow().expr_ty(receiver);
+        let self_ty = self.typeck_results.borrow().expr_ty_opt(receiver)?;
         let name = method_path.ident.name;
         let is_as_ref_able = match self_ty.peel_refs().kind() {
             ty::Adt(def, _) => {

tests/ui/closures/closure-arg-type-mismatch-method-receiver.rs

@@ -0,0 +1,13 @@
+// Regression test for https://github.com/rust-lang/rust/issues/156299.
+
+struct A;
+
+fn foo(_: &A) {}
+
+fn test_foo() {
+    (|a: A| foo(a)).bar();
+        //~^ ERROR mismatched types
+        //~| ERROR no method named `bar` found
+}
+
+fn main() {}

tests/ui/closures/closure-arg-type-mismatch-method-receiver.stderr

@@ -0,0 +1,28 @@
+error[E0308]: mismatched types
+  --> $DIR/closure-arg-type-mismatch-method-receiver.rs:8:17
+   |
+LL |     (|a: A| foo(a)).bar();
+   |             --- ^ expected `&A`, found `A`
+   |             |
+   |             arguments to this function are incorrect
+   |
+note: function defined here
+  --> $DIR/closure-arg-type-mismatch-method-receiver.rs:5:4
+   |
+LL | fn foo(_: &A) {}
+   |    ^^^ -----
+help: consider borrowing here
+   |
+LL |     (|a: A| foo(&a)).bar();
+   |                 +
+
+error[E0599]: no method named `bar` found for closure `{closure@$DIR/closure-arg-type-mismatch-method-receiver.rs:8:6: 8:12}` in the current scope
+  --> $DIR/closure-arg-type-mismatch-method-receiver.rs:8:21
+   |
+LL |     (|a: A| foo(a)).bar();
+   |                     ^^^ method not found in `{closure@$DIR/closure-arg-type-mismatch-method-receiver.rs:8:6: 8:12}`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0308, E0599.
+For more information about an error, try `rustc --explain E0308`.