add the logic for when other_ty is FnDef

src/librustc_typeck/check/op.rs

@@ -333,18 +333,22 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                 lhs_ty);
 
                             if !lhs_expr.span.eq(&rhs_expr.span) {
-                                self.add_type_neq_err_label(&mut err,
+                                self.add_type_neq_err_label(
+                                    &mut err,
                                     lhs_expr.span,
                                     lhs_ty,
                                     rhs_ty,
                                     op,
-                                                            is_assign);
+                                    is_assign
-                                self.add_type_neq_err_label(&mut err,
+                                );
+                                self.add_type_neq_err_label(
+                                    &mut err,
                                     rhs_expr.span,
                                     rhs_ty,
                                     lhs_ty,
                                     op,
-                                                            is_assign);
+                                    is_assign
+                                );
                             }
 
                             let mut suggested_deref = false;
@@ -447,21 +451,35 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
             };
 
+            let other_ty = if let FnDef(def_id, _) = other_ty.sty {
+                let hir_id = &self.tcx.hir().as_local_hir_id(def_id).unwrap();
+                match self.tcx.typeck_tables_of(def_id).liberated_fn_sigs().get(*hir_id) {
+                    Some(f) => f.clone().output(),
+                    None => {
+                        bug!("No fn-sig entry for def_id={:?}", def_id);
+                    }
+                }
+            } else {
+                other_ty
+            };
+
             if self.lookup_op_method(fn_sig.output(),
                                     &[other_ty],
                                     Op::Binary(op, is_assign))
                     .is_ok() {
-                let variable_snippet = if fn_sig.inputs().len() > 0 {
+                let (variable_snippet, applicability) = if fn_sig.inputs().len() > 0 {
-                    format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap())
+                    (format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap()),
+                    Applicability::HasPlaceholders)
                 } else {
-                    format!("{}()", source_map.span_to_snippet(span).unwrap())
+                    (format!("{}()", source_map.span_to_snippet(span).unwrap()),
+                    Applicability::MaybeIncorrect)
                 };
 
                 err.span_suggestion(
                     span,
-                    "did you forget",
+                    "you might have forgotten to call this function",
                     variable_snippet,
-                    Applicability::MachineApplicable,
+                    applicability,
                 );
             }
         }

src/test/ui/fn/fn-compare-mismatch.stderr

@@ -7,6 +7,14 @@ LL |     let x = f == g;
    |             fn() {main::f}
    |
    = note: an implementation of `std::cmp::PartialEq` might be missing for `fn() {main::f}`
+help: you might have forgotten to call this function
+   |
+LL |     let x = f() == g;
+   |             ^^^
+help: you might have forgotten to call this function
+   |
+LL |     let x = f == g();
+   |                  ^^^
 
 error[E0308]: mismatched types
   --> $DIR/fn-compare-mismatch.rs:4:18

src/test/ui/issues/issue-59488.rs

@@ -16,4 +16,11 @@ fn main() {
     bar > 13;
     //~^ ERROR 16:9: 16:10: binary operation `>` cannot be applied to type `fn(i64) -> i64 {bar}` [E0369]
     //~| ERROR 16:11: 16:13: mismatched types [E0308]
+
+    foo > foo;
+    //~^ ERROR 20:9: 20:10: binary operation `>` cannot be applied to type `fn() -> i32 {foo}` [E0369]
+
+    foo > bar;
+    //~^ ERROR 23:9: 23:10: binary operation `>` cannot be applied to type `fn() -> i32 {foo}` [E0369]
+    //~| ERROR 23:11: 23:14: mismatched types [E0308]
 }

src/test/ui/issues/issue-59488.stderr

@@ -5,7 +5,7 @@ LL |     foo > 12;
    |     --- ^ -- {integer}
    |     |
    |     fn() -> i32 {foo}
-   |     help: did you forget: `foo()`
+   |     help: you might have forgotten to call this function: `foo()`
    |
    = note: an implementation of `std::cmp::PartialOrd` might be missing for `fn() -> i32 {foo}`
 
@@ -25,7 +25,7 @@ LL |     bar > 13;
    |     --- ^ -- {integer}
    |     |
    |     fn(i64) -> i64 {bar}
-   |     help: did you forget: `bar( /* arguments */ )`
+   |     help: you might have forgotten to call this function: `bar( /* arguments */ )`
    |
    = note: an implementation of `std::cmp::PartialOrd` might be missing for `fn(i64) -> i64 {bar}`
 
@@ -38,7 +38,44 @@ LL |     bar > 13;
    = note: expected type `fn(i64) -> i64 {bar}`
               found type `i64`
 
-error: aborting due to 4 previous errors
+error[E0369]: binary operation `>` cannot be applied to type `fn() -> i32 {foo}`
+  --> $DIR/issue-59488.rs:20:9
+   |
+LL |     foo > foo;
+   |     --- ^ --- fn() -> i32 {foo}
+   |     |
+   |     fn() -> i32 {foo}
+   |
+   = note: an implementation of `std::cmp::PartialOrd` might be missing for `fn() -> i32 {foo}`
+help: you might have forgotten to call this function
+   |
+LL |     foo() > foo;
+   |     ^^^^^
+help: you might have forgotten to call this function
+   |
+LL |     foo > foo();
+   |           ^^^^^
+
+error[E0369]: binary operation `>` cannot be applied to type `fn() -> i32 {foo}`
+  --> $DIR/issue-59488.rs:23:9
+   |
+LL |     foo > bar;
+   |     --- ^ --- fn(i64) -> i64 {bar}
+   |     |
+   |     fn() -> i32 {foo}
+   |
+   = note: an implementation of `std::cmp::PartialOrd` might be missing for `fn() -> i32 {foo}`
+
+error[E0308]: mismatched types
+  --> $DIR/issue-59488.rs:23:11
+   |
+LL |     foo > bar;
+   |           ^^^ expected fn item, found a different fn item
+   |
+   = note: expected type `fn() -> i32 {foo}`
+              found type `fn(i64) -> i64 {bar}`
+
+error: aborting due to 7 previous errors
 
 Some errors occurred: E0308, E0369.
 For more information about an error, try `rustc --explain E0308`.