Fix ICE when lookup method in trait for type that have bound vars

compiler/rustc_typeck/src/check/_match.rs

@@ -31,7 +31,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => (false, false, false),
         };
 
-        // Type check the descriminant and get its type.
+        // Type check the discriminant and get its type.
         let scrutinee_ty = if force_scrutinee_bool {
             // Here we want to ensure:
             //

compiler/rustc_typeck/src/check/op.rs

@@ -503,8 +503,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if !self.tcx.has_typeck_results(def_id) {
                 return false;
             }
-            // We're emitting a suggestion, so we can just ignore regions
-            let fn_sig = self.tcx.fn_sig(def_id).skip_binder();
+            // FIXME: Instead of exiting early when encountering bound vars in
+            // the function signature, consider keeping the binder here and
+            // propagating it downwards.
+            let fn_sig = if let Some(fn_sig) = self.tcx.fn_sig(def_id).no_bound_vars() {
+                fn_sig
+            } else {
+                return false;
+            };
 
             let other_ty = if let FnDef(def_id, _) = *other_ty.kind() {
                 if !self.tcx.has_typeck_results(def_id) {

src/test/ui/binop/issue-77910-1.rs

@@ -0,0 +1,11 @@
+fn foo(s: &i32) -> &i32 {
+    let xs;
+    xs
+}
+fn main() {
+    let y;
+    // we shouldn't ice with the bound var here.
+    assert_eq!(foo, y);
+    //~^ ERROR binary operation `==` cannot be applied to type
+    //~| ERROR `for<'r> fn(&'r i32) -> &'r i32 {foo}` doesn't implement `Debug`
+}

src/test/ui/binop/issue-77910-1.stderr

@@ -0,0 +1,26 @@
+error[E0369]: binary operation `==` cannot be applied to type `for<'r> fn(&'r i32) -> &'r i32 {foo}`
+  --> $DIR/issue-77910-1.rs:8:5
+   |
+LL |     assert_eq!(foo, y);
+   |     ^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     for<'r> fn(&'r i32) -> &'r i32 {foo}
+   |     _
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: `for<'r> fn(&'r i32) -> &'r i32 {foo}` doesn't implement `Debug`
+  --> $DIR/issue-77910-1.rs:8:5
+   |
+LL |     assert_eq!(foo, y);
+   |     ^^^^^^^^^^^^^^^^^^^ `for<'r> fn(&'r i32) -> &'r i32 {foo}` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+   = help: the trait `Debug` is not implemented for `for<'r> fn(&'r i32) -> &'r i32 {foo}`
+   = note: required because of the requirements on the impl of `Debug` for `&for<'r> fn(&'r i32) -> &'r i32 {foo}`
+   = note: required by `std::fmt::Debug::fmt`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0369.
+For more information about an error, try `rustc --explain E0277`.

src/test/ui/binop/issue-77910-2.rs

@@ -0,0 +1,9 @@
+fn foo(s: &i32) -> &i32 {
+    let xs;
+    xs
+}
+fn main() {
+    let y;
+    if foo == y {}
+    //~^ ERROR binary operation `==` cannot be applied to type
+}

src/test/ui/binop/issue-77910-2.stderr

@@ -0,0 +1,11 @@
+error[E0369]: binary operation `==` cannot be applied to type `for<'r> fn(&'r i32) -> &'r i32 {foo}`
+  --> $DIR/issue-77910-2.rs:7:12
+   |
+LL |     if foo == y {}
+   |        --- ^^ - _
+   |        |
+   |        for<'r> fn(&'r i32) -> &'r i32 {foo}
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0369`.