Do not assemble candidates for auto traits of opaque types in their d…

…efining scope
fmease · Jun 4, 2024 · ad6e85b · ad6e85b
1 parent 4f47342
commit ad6e85b
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Showing 9 changed files with 76 additions and 11 deletions.
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -777,7 +777,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     );
                 }
 
-                ty::Alias(ty::Opaque, _) => {
+                ty::Alias(ty::Opaque, alias) => {
                     if candidates.vec.iter().any(|c| matches!(c, ProjectionCandidate(_))) {
                         // We do not generate an auto impl candidate for `impl Trait`s which already
                         // reference our auto trait.
@@ -792,6 +792,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         // We do not emit auto trait candidates for opaque types in coherence.
                         // Doing so can result in weird dependency cycles.
                         candidates.ambiguous = true;
+                    } else if self.infcx.can_define_opaque_ty(alias.def_id) {
+                        // We do not emit auto trait candidates for opaque types in their defining scope, as
+                        // we need to know the hidden type first, which we can't reliably know within the defining
+                        // scope.
+                        candidates.ambiguous = true;
                     } else {
                         candidates.vec.push(AutoImplCandidate)
                     }

diff --git a/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr b/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr
@@ -1,5 +1,5 @@
 error[E0283]: type annotations needed
-  --> $DIR/auto-trait-selection-freeze.rs:20:16
+  --> $DIR/auto-trait-selection-freeze.rs:19:16
    |
 LL |     if false { is_trait(foo()) } else { Default::default() }
    |                ^^^^^^^^ ----- type must be known at this point
@@ -8,7 +8,7 @@ LL |     if false { is_trait(foo()) } else { Default::default() }
    |
    = note: cannot satisfy `_: Trait<_>`
 note: required by a bound in `is_trait`
-  --> $DIR/auto-trait-selection-freeze.rs:12:16
+  --> $DIR/auto-trait-selection-freeze.rs:11:16
    |
 LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
    |                ^^^^^^^^ required by this bound in `is_trait`

diff --git a/tests/ui/impl-trait/auto-trait-selection-freeze.old.stderr b/tests/ui/impl-trait/auto-trait-selection-freeze.old.stderr
@@ -0,0 +1,26 @@
+error[E0283]: type annotations needed
+  --> $DIR/auto-trait-selection-freeze.rs:19:16
+   |
+LL |     if false { is_trait(foo()) } else { Default::default() }
+   |                ^^^^^^^^ cannot infer type of the type parameter `U` declared on the function `is_trait`
+   |
+note: multiple `impl`s satisfying `impl Sized: Trait<_>` found
+  --> $DIR/auto-trait-selection-freeze.rs:16:1
+   |
+LL | impl<T: Freeze> Trait<u32> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | impl<T> Trait<i32> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+note: required by a bound in `is_trait`
+  --> $DIR/auto-trait-selection-freeze.rs:11:16
+   |
+LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
+   |                ^^^^^^^^ required by this bound in `is_trait`
+help: consider specifying the generic arguments
+   |
+LL |     if false { is_trait::<_, U>(foo()) } else { Default::default() }
+   |                        ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.
diff --git a/tests/ui/impl-trait/auto-trait-selection-freeze.rs b/tests/ui/impl-trait/auto-trait-selection-freeze.rs
@@ -3,7 +3,6 @@
 
 //@ revisions: next old
 //@[next] compile-flags: -Znext-solver
-//@[old]check-pass
 
 #![feature(freeze)]
 
@@ -18,7 +17,7 @@ impl<T: Freeze> Trait<u32> for T {}
 impl<T> Trait<i32> for T {}
 fn foo() -> impl Sized {
     if false { is_trait(foo()) } else { Default::default() }
-    //[next]~^ ERROR: type annotations needed
+    //~^ ERROR: type annotations needed
 }
 
 fn main() {}
diff --git a/tests/ui/impl-trait/auto-trait-selection.next.stderr b/tests/ui/impl-trait/auto-trait-selection.next.stderr
@@ -1,5 +1,5 @@
 error[E0283]: type annotations needed
-  --> $DIR/auto-trait-selection.rs:16:16
+  --> $DIR/auto-trait-selection.rs:15:16
    |
 LL |     if false { is_trait(foo()) } else { Default::default() }
    |                ^^^^^^^^ ----- type must be known at this point
@@ -8,7 +8,7 @@ LL |     if false { is_trait(foo()) } else { Default::default() }
    |
    = note: cannot satisfy `_: Trait<_>`
 note: required by a bound in `is_trait`
-  --> $DIR/auto-trait-selection.rs:8:16
+  --> $DIR/auto-trait-selection.rs:7:16
    |
 LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
    |                ^^^^^^^^ required by this bound in `is_trait`

diff --git a/tests/ui/impl-trait/auto-trait-selection.old.stderr b/tests/ui/impl-trait/auto-trait-selection.old.stderr
@@ -0,0 +1,26 @@
+error[E0283]: type annotations needed
+  --> $DIR/auto-trait-selection.rs:15:16
+   |
+LL |     if false { is_trait(foo()) } else { Default::default() }
+   |                ^^^^^^^^ cannot infer type of the type parameter `U` declared on the function `is_trait`
+   |
+note: multiple `impl`s satisfying `impl Sized: Trait<_>` found
+  --> $DIR/auto-trait-selection.rs:12:1
+   |
+LL | impl<T: Send> Trait<u32> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | impl<T> Trait<i32> for T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+note: required by a bound in `is_trait`
+  --> $DIR/auto-trait-selection.rs:7:16
+   |
+LL | fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
+   |                ^^^^^^^^ required by this bound in `is_trait`
+help: consider specifying the generic arguments
+   |
+LL |     if false { is_trait::<_, U>(foo()) } else { Default::default() }
+   |                        ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.
diff --git a/tests/ui/impl-trait/auto-trait-selection.rs b/tests/ui/impl-trait/auto-trait-selection.rs
@@ -3,7 +3,6 @@
 
 //@ revisions: next old
 //@[next] compile-flags: -Znext-solver
-//@[old]check-pass
 
 fn is_trait<T: Trait<U>, U: Default>(_: T) -> U {
     Default::default()
@@ -14,7 +13,7 @@ impl<T: Send> Trait<u32> for T {}
 impl<T> Trait<i32> for T {}
 fn foo() -> impl Sized {
     if false { is_trait(foo()) } else { Default::default() }
-    //[next]~^ ERROR: type annotations needed
+    //~^ ERROR: type annotations needed
 }
 
 fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/in-where-clause.rs b/tests/ui/type-alias-impl-trait/in-where-clause.rs
@@ -8,6 +8,7 @@ type Bar = impl Sized;
 fn foo() -> Bar
 where
     Bar: Send,
+    //~^ ERROR: type annotations needed
 {
     [0; 1 + 2]
 }

diff --git a/tests/ui/type-alias-impl-trait/in-where-clause.stderr b/tests/ui/type-alias-impl-trait/in-where-clause.stderr
@@ -25,6 +25,15 @@ LL | type Bar = impl Sized;
    |            ^^^^^^^^^^
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
-error: aborting due to 1 previous error
+error[E0283]: type annotations needed: cannot satisfy `Bar: Send`
+  --> $DIR/in-where-clause.rs:10:10
+   |
+LL |     Bar: Send,
+   |          ^^^^
+   |
+   = note: cannot satisfy `Bar: Send`
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0391`.
+Some errors have detailed explanations: E0283, E0391.
+For more information about an error, try `rustc --explain E0283`.