prevent opaque types from appearing in impl headers

11 files changed, 71 insertions, 42 deletions

diff --git a/compiler/rustc_typeck/src/coherence/orphan.rs b/compiler/rustc_typeck/src/coherence/orphan.rs
index 4b23cc4db85..564c3d31368 100644
--- a/compiler/rustc_typeck/src/coherence/orphan.rs
+++ b/compiler/rustc_typeck/src/coherence/orphan.rs
@@ -141,13 +141,22 @@ fn orphan_check_impl(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGua
         }
     }
 
-    if let ty::Opaque(def_id, _) = *trait_ref.self_ty().kind() {
-        let reported = tcx
-            .sess
-            .struct_span_err(sp, "cannot implement trait on type alias impl trait")
-            .span_note(tcx.def_span(def_id), "type alias impl trait defined here")
-            .emit();
-        return Err(reported);
+    // Ensure no opaque types are present in this impl header. See issues #76202 and #86411 for examples,
+    // and #84660 where it would otherwise allow unsoundness.
+    if trait_ref.has_opaque_types() {
+        for ty in trait_ref.substs {
+            for ty in ty.walk() {
+                let ty::subst::GenericArgKind::Type(ty) = ty.unpack() else { continue };
+                let ty::Opaque(def_id, _) = ty.kind() else { continue };
+                let reported = tcx
+                    .sess
+                    .struct_span_err(sp, "cannot implement trait on type alias impl trait")
+                    .span_note(tcx.def_span(def_id), "type alias impl trait defined here")
+                    .emit();
+                return Err(reported);
+            }
+        }
+        span_bug!(sp, "opque type not found, but `has_opaque_types` is set")
     }
 
     Ok(())
diff --git a/src/test/ui/impl-trait/auto-trait.rs b/src/test/ui/impl-trait/auto-trait.rs
index 35994e4a5ba..afa95645a27 100644
--- a/src/test/ui/impl-trait/auto-trait.rs
+++ b/src/test/ui/impl-trait/auto-trait.rs
@@ -20,6 +20,7 @@ impl<T: Send> AnotherTrait for T {}
 // in the future.)
 impl AnotherTrait for D<OpaqueType> {
     //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+    //~| ERROR cannot implement trait on type alias impl trait
 }
 
 fn main() {}
diff --git a/src/test/ui/impl-trait/auto-trait.stderr b/src/test/ui/impl-trait/auto-trait.stderr
index 81009413c9a..9171cfca5b1 100644
--- a/src/test/ui/impl-trait/auto-trait.stderr
+++ b/src/test/ui/impl-trait/auto-trait.stderr
@@ -1,3 +1,15 @@
+error: cannot implement trait on type alias impl trait
+  --> $DIR/auto-trait.rs:21:1
+   |
+LL | impl AnotherTrait for D<OpaqueType> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: type alias impl trait defined here
+  --> $DIR/auto-trait.rs:7:19
+   |
+LL | type OpaqueType = impl OpaqueTrait;
+   |                   ^^^^^^^^^^^^^^^^
+
 error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $DIR/auto-trait.rs:21:1
    |
@@ -7,6 +19,6 @@ LL | impl<T: Send> AnotherTrait for T {}
 LL | impl AnotherTrait for D<OpaqueType> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0119`.
diff --git a/src/test/ui/impl-trait/negative-reasoning.rs b/src/test/ui/impl-trait/negative-reasoning.rs
index 70e24a3a9d0..da69bb349ae 100644
--- a/src/test/ui/impl-trait/negative-reasoning.rs
+++ b/src/test/ui/impl-trait/negative-reasoning.rs
@@ -18,6 +18,7 @@ impl<T: std::fmt::Debug> AnotherTrait for T {}
 // This is in error, because we cannot assume that `OpaqueType: !Debug`
 impl AnotherTrait for D<OpaqueType> {
     //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+    //~| ERROR cannot implement trait on type alias impl trait
 }
 
 fn main() {}
diff --git a/src/test/ui/impl-trait/negative-reasoning.stderr b/src/test/ui/impl-trait/negative-reasoning.stderr
index 6b8cc9e7374..1a7233bca5c 100644
--- a/src/test/ui/impl-trait/negative-reasoning.stderr
+++ b/src/test/ui/impl-trait/negative-reasoning.stderr
@@ -1,3 +1,15 @@
+error: cannot implement trait on type alias impl trait
+  --> $DIR/negative-reasoning.rs:19:1
+   |
+LL | impl AnotherTrait for D<OpaqueType> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: type alias impl trait defined here
+  --> $DIR/negative-reasoning.rs:7:19
+   |
+LL | type OpaqueType = impl OpaqueTrait;
+   |                   ^^^^^^^^^^^^^^^^
+
 error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $DIR/negative-reasoning.rs:19:1
    |
@@ -9,6 +21,6 @@ LL | impl AnotherTrait for D<OpaqueType> {
    |
    = note: upstream crates may add a new impl of trait `std::fmt::Debug` for type `OpaqueType` in future versions
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0119`.
diff --git a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs
index 6b200d7e3a8..621c4ea6e0d 100644
--- a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs
+++ b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs
@@ -5,13 +5,14 @@ type Foo = impl PartialEq<(Foo, i32)>;
 struct Bar;
 
 impl PartialEq<(Foo, i32)> for Bar {
+//~^ ERROR cannot implement trait on type alias impl trait
     fn eq(&self, _other: &(Foo, i32)) -> bool {
         true
     }
 }
 
 fn foo() -> Foo {
-    Bar //~ ERROR can't compare `Bar` with `(Bar, i32)`
+    Bar
 }
 
 fn main() {}
diff --git a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.stderr b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.stderr
index 6cd63db44fa..4e8d4cce0a1 100644
--- a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.stderr
+++ b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle-2.stderr
@@ -1,12 +1,14 @@
-error[E0277]: can't compare `Bar` with `(Bar, i32)`
-  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs:14:5
+error: cannot implement trait on type alias impl trait
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs:7:1
    |
-LL |     Bar
-   |     ^^^ no implementation for `Bar == (Bar, i32)`
+LL | impl PartialEq<(Foo, i32)> for Bar {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: the trait `PartialEq<(Bar, i32)>` is not implemented for `Bar`
-   = help: the trait `PartialEq<(Foo, i32)>` is implemented for `Bar`
+note: type alias impl trait defined here
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle-2.rs:3:12
+   |
+LL | type Foo = impl PartialEq<(Foo, i32)>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.rs b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.rs
index 6aa832cde71..df7966f00e1 100644
--- a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.rs
+++ b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.rs
@@ -2,7 +2,6 @@
 
 mod a {
     type Foo = impl PartialEq<(Foo, i32)>;
-    //~^ ERROR unconstrained opaque type
 
     struct Bar;
 
@@ -15,13 +14,12 @@ mod a {
 
 mod b {
     type Foo = impl PartialEq<(Foo, i32)>;
-    //~^ ERROR unconstrained opaque type
 
     struct Bar;
 
     impl PartialEq<(Foo, i32)> for Bar {
+        //~^ ERROR cannot implement trait on type alias impl trait
         fn eq(&self, _other: &(Bar, i32)) -> bool {
-            //~^ ERROR impl has stricter requirements than trait
             true
         }
     }
diff --git a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
index 19d5cdb9d0a..ccb0bc0a366 100644
--- a/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
+++ b/src/test/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
@@ -1,25 +1,14 @@
-error: unconstrained opaque type
-  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:4:16
+error: cannot implement trait on type alias impl trait
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:20:5
    |
-LL |     type Foo = impl PartialEq<(Foo, i32)>;
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     impl PartialEq<(Foo, i32)> for Bar {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `Foo` must be used in combination with a concrete type within the same module
-
-error: unconstrained opaque type
-  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:17:16
+note: type alias impl trait defined here
+  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:16:16
    |
 LL |     type Foo = impl PartialEq<(Foo, i32)>;
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: `Foo` must be used in combination with a concrete type within the same module
-
-error[E0276]: impl has stricter requirements than trait
-  --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:23:9
-   |
-LL |         fn eq(&self, _other: &(Bar, i32)) -> bool {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `b::Bar: PartialEq<(b::Bar, i32)>`
 
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0276`.
diff --git a/src/test/ui/type-alias-impl-trait/nested-tait-inference3.rs b/src/test/ui/type-alias-impl-trait/nested-tait-inference3.rs
index fbab5470b4f..ebf3a99bbf9 100644
--- a/src/test/ui/type-alias-impl-trait/nested-tait-inference3.rs
+++ b/src/test/ui/type-alias-impl-trait/nested-tait-inference3.rs
@@ -4,11 +4,11 @@
 use std::fmt::Debug;
 
 type FooX = impl Debug;
-//~^ unconstrained opaque type
 
 trait Foo<A> { }
 
 impl Foo<FooX> for () { }
+//~^ cannot implement trait on type alias impl trait
 
 fn foo() -> impl Foo<FooX> {
     ()
diff --git a/src/test/ui/type-alias-impl-trait/nested-tait-inference3.stderr b/src/test/ui/type-alias-impl-trait/nested-tait-inference3.stderr
index b1d947a9ccf..bf1582639a2 100644
--- a/src/test/ui/type-alias-impl-trait/nested-tait-inference3.stderr
+++ b/src/test/ui/type-alias-impl-trait/nested-tait-inference3.stderr
@@ -1,10 +1,14 @@
-error: unconstrained opaque type
+error: cannot implement trait on type alias impl trait
+  --> $DIR/nested-tait-inference3.rs:10:1
+   |
+LL | impl Foo<FooX> for () { }
+   | ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: type alias impl trait defined here
   --> $DIR/nested-tait-inference3.rs:6:13
    |
 LL | type FooX = impl Debug;
    |             ^^^^^^^^^^
-   |
-   = note: `FooX` must be used in combination with a concrete type within the same module
 
 error: aborting due to previous error