From 0e82aaeb6799041991c54fb9ff37b5c20a5c6146 Mon Sep 17 00:00:00 2001
From: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Date: Tue, 9 Jan 2024 18:13:19 +0000
Subject: [PATCH] Avoid follow up errors

---
 .../src/collect/type_of/opaque.rs             | 15 +++++++++++
 tests/ui/type-alias-impl-trait/issue-77179.rs |  2 --
 .../type-alias-impl-trait/issue-77179.stderr  | 26 ++-----------------
 3 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
index da7279967dac1..1f7ca48234a24 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
@@ -134,6 +134,21 @@ impl TaitConstraintLocator<'_> {
             debug!("no constraint: no typeck results");
             return;
         }
+
+        if let Some(hir_sig) = self.tcx.hir_node_by_def_id(item_def_id).fn_decl() {
+            if hir_sig.output.get_infer_ret_ty().is_some() {
+                let guar = self.tcx.dcx().span_delayed_bug(
+                    hir_sig.output.span(),
+                    "inferring return types and opaque types do not mix well",
+                );
+                self.found = Some(ty::OpaqueHiddenType {
+                    span: DUMMY_SP,
+                    ty: Ty::new_error(self.tcx, guar),
+                });
+                return;
+            }
+        }
+
         // Calling `mir_borrowck` can lead to cycle errors through
         // const-checking, avoid calling it if we don't have to.
         // ```rust
diff --git a/tests/ui/type-alias-impl-trait/issue-77179.rs b/tests/ui/type-alias-impl-trait/issue-77179.rs
index 6e2ce76632fdc..093aeb4b27911 100644
--- a/tests/ui/type-alias-impl-trait/issue-77179.rs
+++ b/tests/ui/type-alias-impl-trait/issue-77179.rs
@@ -6,9 +6,7 @@ type Pointer<T> = impl std::ops::Deref<Target = T>;
 
 fn test() -> Pointer<_> {
     //~^ ERROR: the placeholder `_` is not allowed within types
-    //~| ERROR: non-defining opaque type use in defining scope
     Box::new(1)
-    //~^ ERROR expected generic type parameter, found `i32`
 }
 
 fn main() {
diff --git a/tests/ui/type-alias-impl-trait/issue-77179.stderr b/tests/ui/type-alias-impl-trait/issue-77179.stderr
index c5b7c4178e473..68dd6570d00c0 100644
--- a/tests/ui/type-alias-impl-trait/issue-77179.stderr
+++ b/tests/ui/type-alias-impl-trait/issue-77179.stderr
@@ -7,28 +7,6 @@ LL | fn test() -> Pointer<_> {
    |              |       not allowed in type signatures
    |              help: replace with the correct return type: `Pointer<i32>`
 
-error[E0792]: non-defining opaque type use in defining scope
-  --> $DIR/issue-77179.rs:7:14
-   |
-LL | fn test() -> Pointer<_> {
-   |              ^^^^^^^^^^ argument `i32` is not a generic parameter
-   |
-note: for this opaque type
-  --> $DIR/issue-77179.rs:5:19
-   |
-LL | type Pointer<T> = impl std::ops::Deref<Target = T>;
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error[E0792]: expected generic type parameter, found `i32`
-  --> $DIR/issue-77179.rs:10:5
-   |
-LL | type Pointer<T> = impl std::ops::Deref<Target = T>;
-   |              - this generic parameter must be used with a generic type parameter
-...
-LL |     Box::new(1)
-   |     ^^^^^^^^^^^
-
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0121, E0792.
-For more information about an error, try `rustc --explain E0121`.
+For more information about this error, try `rustc --explain E0121`.