From c37eee38584ac6bfd83f19a29c640fea96e02c3f Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 3 Oct 2024 17:16:03 -0400
Subject: [PATCH] Suppress redundant/wrong error when RTN bound fails to
 resolve

---
 .../src/hir_ty_lowering/bounds.rs             |  9 +++++++++
 .../return-type-notation/not-a-method.rs      |  2 --
 .../return-type-notation/not-a-method.stderr  | 20 ++++---------------
 tests/ui/error-codes/E0801.rs                 |  1 -
 tests/ui/error-codes/E0801.stderr             |  8 +-------
 5 files changed, 14 insertions(+), 26 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index 45cd46e3df296..6b2d5f63370df 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -558,6 +558,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     Err(guar) => Ty::new_error(tcx, guar),
                 }
             }
+            hir::QPath::Resolved(
+                _,
+                hir::Path { res: Res::Err, segments: [.., item_segment], .. },
+            ) if item_segment.args.is_some_and(|args| {
+                matches!(args.parenthesized, hir::GenericArgsParentheses::ReturnTypeNotation)
+            }) =>
+            {
+                Ty::new_error_with_message(tcx, hir_ty.span, "bad resolution for RTN")
+            }
             _ => self.lower_ty(hir_ty),
         }
     }
diff --git a/tests/ui/associated-type-bounds/return-type-notation/not-a-method.rs b/tests/ui/associated-type-bounds/return-type-notation/not-a-method.rs
index 2f3fe115e1093..d0aa2e872ce1a 100644
--- a/tests/ui/associated-type-bounds/return-type-notation/not-a-method.rs
+++ b/tests/ui/associated-type-bounds/return-type-notation/not-a-method.rs
@@ -6,7 +6,6 @@ fn not_a_method()
 where
     function(..): Send,
     //~^ ERROR expected associated function, found function `function`
-    //~| ERROR return type notation not allowed in this position yet
 {
 }
 
@@ -26,7 +25,6 @@ fn maybe_method_overlaps<T: Tr>()
 where
     method(..): Send,
     //~^ ERROR cannot find associated function `method` in this scope
-    //~| ERROR return type notation not allowed in this position yet
 {
 }
 
diff --git a/tests/ui/associated-type-bounds/return-type-notation/not-a-method.stderr b/tests/ui/associated-type-bounds/return-type-notation/not-a-method.stderr
index dfddd73912ab6..7840d706a31e2 100644
--- a/tests/ui/associated-type-bounds/return-type-notation/not-a-method.stderr
+++ b/tests/ui/associated-type-bounds/return-type-notation/not-a-method.stderr
@@ -5,36 +5,24 @@ LL |     function(..): Send,
    |     ^^^^^^^^^^^^ not a associated function
 
 error[E0573]: expected type, found function `function`
-  --> $DIR/not-a-method.rs:15:5
+  --> $DIR/not-a-method.rs:14:5
    |
 LL |     function(): Send,
    |     ^^^^^^^^^^ not a type
 
 error[E0802]: cannot find associated function `method` in this scope
-  --> $DIR/not-a-method.rs:27:5
+  --> $DIR/not-a-method.rs:26:5
    |
 LL |     method(..): Send,
    |     ^^^^^^ not found in this scope
 
 error[E0412]: cannot find type `method` in this scope
-  --> $DIR/not-a-method.rs:36:5
+  --> $DIR/not-a-method.rs:34:5
    |
 LL |     method(): Send,
    |     ^^^^^^ not found in this scope
 
-error: return type notation not allowed in this position yet
-  --> $DIR/not-a-method.rs:7:5
-   |
-LL |     function(..): Send,
-   |     ^^^^^^^^^^^^
-
-error: return type notation not allowed in this position yet
-  --> $DIR/not-a-method.rs:27:5
-   |
-LL |     method(..): Send,
-   |     ^^^^^^^^^^
-
-error: aborting due to 6 previous errors
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0412, E0573, E0801, E0802.
 For more information about an error, try `rustc --explain E0412`.
diff --git a/tests/ui/error-codes/E0801.rs b/tests/ui/error-codes/E0801.rs
index 6cba6c0027313..eab1064c6bf5d 100644
--- a/tests/ui/error-codes/E0801.rs
+++ b/tests/ui/error-codes/E0801.rs
@@ -4,7 +4,6 @@ fn test()
 where
     test(..): Send,
     //~^ ERROR expected associated function, found function `test`
-    //~| ERROR return type notation not allowed in this position yet
 {
 }
 
diff --git a/tests/ui/error-codes/E0801.stderr b/tests/ui/error-codes/E0801.stderr
index 7a5b7ecd488d9..de5a6766b5917 100644
--- a/tests/ui/error-codes/E0801.stderr
+++ b/tests/ui/error-codes/E0801.stderr
@@ -4,12 +4,6 @@ error[E0801]: expected associated function, found function `test`
 LL |     test(..): Send,
    |     ^^^^^^^^ not a associated function
 
-error: return type notation not allowed in this position yet
-  --> $DIR/E0801.rs:5:5
-   |
-LL |     test(..): Send,
-   |     ^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0801`.