When checking whether an impl applies, constrain hidden types of opaque types.

oli-obk · oli-obk · commit e82a1e511d91 · 2024-04-17T09:29:27.000Z
We already handle this case this way on the coherence side, and it matches the new solver's behaviour. While there is some breakage around type-alias-impl-trait (see new "type annotations needed" in tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs), no stable code breaks, and no new stable code is accepted.
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2524,7 +2524,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         let InferOk { obligations, .. } = self
             .infcx
             .at(&cause, obligation.param_env)
-            .eq(DefineOpaqueTypes::No, placeholder_obligation_trait_ref, impl_trait_ref)
+            .eq(DefineOpaqueTypes::Yes, placeholder_obligation_trait_ref, impl_trait_ref)
             .map_err(|e| {
                 debug!("match_impl: failed eq_trait_refs due to `{}`", e.to_string(self.tcx()))
             })?;
diff --git a/tests/ui/impl-trait/equality.rs b/tests/ui/impl-trait/equality.rs
@@ -22,7 +22,7 @@ fn sum_to(n: u32) -> impl Foo {
         0
     } else {
         n + sum_to(n - 1)
-        //~^ ERROR cannot add `impl Foo` to `u32`
+        //~^ ERROR cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
     }
 }
 
@@ -32,12 +32,15 @@ trait Leak: Sized {
 }
 impl<T> Leak for T {
     default type T = ();
-    default fn leak(self) -> Self::T { panic!() }
+    default fn leak(self) -> Self::T {
+        panic!()
+    }
 }
 impl Leak for i32 {
     type T = i32;
-    fn leak(self) -> i32 { self }
+    fn leak(self) -> i32 {
+        self
+    }
 }
 
-fn main() {
-}
+fn main() {}
diff --git a/tests/ui/impl-trait/equality.stderr b/tests/ui/impl-trait/equality.stderr
@@ -22,20 +22,13 @@ help: change the type of the numeric literal from `u32` to `i32`
 LL |     0_i32
    |       ~~~
 
-error[E0277]: cannot add `impl Foo` to `u32`
+error[E0284]: type annotations needed: cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
   --> $DIR/equality.rs:24:11
    |
 LL |         n + sum_to(n - 1)
-   |           ^ no implementation for `u32 + impl Foo`
-   |
-   = help: the trait `Add<impl Foo>` is not implemented for `u32`
-   = help: the following other types implement trait `Add<Rhs>`:
-             <&'a u32 as Add<u32>>
-             <&u32 as Add<&u32>>
-             <u32 as Add<&u32>>
-             <u32 as Add>
+   |           ^ cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
 
 error: aborting due to 2 previous errors; 1 warning emitted
 
-Some errors have detailed explanations: E0277, E0308.
-For more information about an error, try `rustc --explain E0277`.
+Some errors have detailed explanations: E0284, E0308.
+For more information about an error, try `rustc --explain E0284`.
diff --git a/tests/ui/impl-trait/nested_impl_trait.stderr b/tests/ui/impl-trait/nested_impl_trait.stderr
@@ -46,19 +46,23 @@ error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfie
   --> $DIR/nested_impl_trait.rs:6:46
    |
 LL | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
-   |                                              ^^^^^^^^^^^^^^^^^^^^^ the trait `From<impl Into<u32>>` is not implemented for `impl Into<u32>`, which is required by `impl Into<u32>: Into<impl Debug>`
+   |                                              ^^^^^^^^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `impl Into<u32>`
    |
-   = help: the trait `Into<U>` is implemented for `T`
-   = note: required for `impl Into<u32>` to implement `Into<impl Debug>`
+help: consider further restricting this bound
+   |
+LL | fn bad_in_ret_position(x: impl Into<u32> + std::fmt::Debug) -> impl Into<impl Debug> { x }
+   |                                          +++++++++++++++++
 
 error[E0277]: the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfied
   --> $DIR/nested_impl_trait.rs:19:34
    |
 LL |     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
-   |                                  ^^^^^^^^^^^^^^^^^^^^^ the trait `From<impl Into<u32>>` is not implemented for `impl Into<u32>`, which is required by `impl Into<u32>: Into<impl Debug>`
+   |                                  ^^^^^^^^^^^^^^^^^^^^^ the trait `Debug` is not implemented for `impl Into<u32>`
+   |
+help: consider further restricting this bound
    |
-   = help: the trait `Into<U>` is implemented for `T`
-   = note: required for `impl Into<u32>` to implement `Into<impl Debug>`
+LL |     fn bad(x: impl Into<u32> + std::fmt::Debug) -> impl Into<impl Debug> { x }
+   |                              +++++++++++++++++
 
 error: aborting due to 7 previous errors
 
diff --git a/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration.rs b/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration.rs
@@ -11,7 +11,7 @@ impl PartialEq<(Bar, i32)> for Bar {
 }
 
 fn foo() -> Foo {
-    //~^ ERROR can't compare `Bar` with `(Foo, i32)`
+    //~^ ERROR overflow evaluating the requirement `Bar: PartialEq<(Foo, i32)>`
     Bar
 }
 
diff --git a/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration.stderr b/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration.stderr
@@ -1,15 +1,9 @@
-error[E0277]: can't compare `Bar` with `(Foo, i32)`
+error[E0275]: overflow evaluating the requirement `Bar: PartialEq<(Foo, i32)>`
   --> $DIR/recursive-type-alias-impl-trait-declaration.rs:13:13
    |
 LL | fn foo() -> Foo {
-   |             ^^^ no implementation for `Bar == (Foo, i32)`
-LL |
-LL |     Bar
-   |     --- return type was inferred to be `Bar` here
-   |
-   = help: the trait `PartialEq<(Foo, i32)>` is not implemented for `Bar`
-   = help: the trait `PartialEq<(Bar, i32)>` is implemented for `Bar`
+   |             ^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0275`.
diff --git a/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.current.stderr b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.current.stderr
@@ -0,0 +1,28 @@
+error[E0119]: conflicting implementations of trait `Trait<Bar, _>`
+  --> $DIR/issue-84660-unsoundness.rs:28:1
+   |
+LL | impl<In, Out> Trait<Bar, In> for Out {
+   | ------------------------------------ first implementation here
+...
+LL | impl<In, Out> Trait<(), In> for Out {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error[E0282]: type annotations needed
+  --> $DIR/issue-84660-unsoundness.rs:22:5
+   |
+LL |     fn convert(_i: In) -> Self::Out {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
+   |
+note: the requirement `_ <: _` appears on the `impl`'s method `convert` but not on the corresponding trait's method
+  --> $DIR/issue-84660-unsoundness.rs:17:8
+   |
+LL | trait Trait<T, In> {
+   |       ----- in this trait
+LL |     type Out;
+LL |     fn convert(i: In) -> Self::Out;
+   |        ^^^^^^^ this trait's method doesn't have the requirement `_ <: _`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0119, E0282.
+For more information about an error, try `rustc --explain E0119`.
diff --git a/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.next.stderr b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.next.stderr
@@ -0,0 +1,23 @@
+error[E0284]: type annotations needed: cannot satisfy `<Out as Trait<Bar, In>>::Out == ()`
+  --> $DIR/issue-84660-unsoundness.rs:22:37
+   |
+LL |       fn convert(_i: In) -> Self::Out {
+   |  _____________________________________^
+LL | |
+LL | |         unreachable!();
+LL | |     }
+   | |_____^ cannot satisfy `<Out as Trait<Bar, In>>::Out == ()`
+
+error[E0119]: conflicting implementations of trait `Trait<Bar, _>`
+  --> $DIR/issue-84660-unsoundness.rs:28:1
+   |
+LL | impl<In, Out> Trait<Bar, In> for Out {
+   | ------------------------------------ first implementation here
+...
+LL | impl<In, Out> Trait<(), In> for Out {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0119, E0284.
+For more information about an error, try `rustc --explain E0119`.
diff --git a/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs
@@ -1,6 +1,10 @@
 // Another example from issue #84660, this time weaponized as a safe transmute: an opaque type in an
 // impl header being accepted was used to create unsoundness.
 
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
 #![feature(type_alias_impl_trait)]
 
 trait Foo {}
@@ -16,11 +20,13 @@ trait Trait<T, In> {
 impl<In, Out> Trait<Bar, In> for Out {
     type Out = Out;
     fn convert(_i: In) -> Self::Out {
+        //~^ ERROR: type annotations needed
         unreachable!();
     }
 }
 
-impl<In, Out> Trait<(), In> for Out { //~ ERROR conflicting implementations of trait `Trait<Bar, _>`
+impl<In, Out> Trait<(), In> for Out {
+    //~^ ERROR conflicting implementations of trait `Trait<Bar, _>`
     type Out = In;
     fn convert(i: In) -> Self::Out {
         i
diff --git a/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.stderr b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.stderr
diff --git a/tests/ui/type-alias-impl-trait/nested-tait-inference.rs b/tests/ui/type-alias-impl-trait/nested-tait-inference.rs
@@ -1,18 +1,21 @@
 #![feature(type_alias_impl_trait)]
 #![allow(dead_code)]
 
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@check-pass
+
 use std::fmt::Debug;
 
 type FooX = impl Debug;
 
-trait Foo<A> { }
+trait Foo<A> {}
 
-impl Foo<()> for () { }
+impl Foo<()> for () {}
 
 fn foo() -> impl Foo<FooX> {
-    //~^ ERROR: the trait bound `(): Foo<FooX>` is not satisfied
-    // FIXME(type-alias-impl-trait): We could probably make this work.
     ()
 }
 
-fn main() { }
+fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/nested-tait-inference2.current.stderr b/tests/ui/type-alias-impl-trait/nested-tait-inference2.current.stderr
@@ -0,0 +1,17 @@
+error[E0283]: type annotations needed: cannot satisfy `(): Foo<FooX>`
+  --> $DIR/nested-tait-inference2.rs:17:13
+   |
+LL | fn foo() -> impl Foo<FooX> {
+   |             ^^^^^^^^^^^^^^
+   |
+note: multiple `impl`s satisfying `(): Foo<FooX>` found
+  --> $DIR/nested-tait-inference2.rs:14:1
+   |
+LL | impl Foo<()> for () {}
+   | ^^^^^^^^^^^^^^^^^^^
+LL | impl Foo<u32> for () {}
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.
diff --git a/tests/ui/type-alias-impl-trait/nested-tait-inference2.next.stderr b/tests/ui/type-alias-impl-trait/nested-tait-inference2.next.stderr
@@ -0,0 +1,9 @@
+error[E0284]: type annotations needed: cannot satisfy `impl Foo<FooX> == ()`
+  --> $DIR/nested-tait-inference2.rs:19:5
+   |
+LL |     ()
+   |     ^^ cannot satisfy `impl Foo<FooX> == ()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0284`.
diff --git a/tests/ui/type-alias-impl-trait/nested-tait-inference2.rs b/tests/ui/type-alias-impl-trait/nested-tait-inference2.rs
@@ -1,6 +1,10 @@
 #![feature(type_alias_impl_trait)]
 #![allow(dead_code)]
 
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
 use std::fmt::Debug;
 
 type FooX = impl Debug;
@@ -11,8 +15,9 @@ impl Foo<()> for () {}
 impl Foo<u32> for () {}
 
 fn foo() -> impl Foo<FooX> {
-    //~^ ERROR: the trait bound `(): Foo<FooX>` is not satisfied
+    //[current]~^ ERROR: cannot satisfy `(): Foo<FooX>`
     ()
+    //[next]~^ ERROR: cannot satisfy `impl Foo<FooX> == ()`
 }
 
 fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/nested-tait-inference2.stderr b/tests/ui/type-alias-impl-trait/nested-tait-inference2.stderr
diff --git a/tests/ui/type-alias-impl-trait/normalize-hidden-types.current.stderr b/tests/ui/type-alias-impl-trait/normalize-hidden-types.current.stderr
@@ -22,21 +22,17 @@ note: previous use here
 LL |     fn define_1() -> Opaque { dyn_hoops::<_>(0) }
    |                               ^^^^^^^^^^^^^^^^^
 
-error[E0308]: mismatched types
+error: concrete type differs from previous defining opaque type use
   --> $DIR/normalize-hidden-types.rs:43:25
    |
-LL |     type Opaque = impl Sized;
-   |                   ---------- the expected opaque type
-...
 LL |         let _: Opaque = dyn_hoops::<u8>(0);
-   |                ------   ^^^^^^^^^^^^^^^^^^ expected opaque type, found `*const dyn FnOnce(())`
-   |                |
-   |                expected due to this
-   |
-   = note: expected opaque type `typeck::Opaque`
-              found raw pointer `*const (dyn FnOnce(()) + 'static)`
-   = help: consider constraining the associated type `<u8 as Trait>::Gat<'_>` to `()` or calling a method that returns `<u8 as Trait>::Gat<'_>`
-   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+   |                         ^^^^^^^^^^^^^^^^^^ expected `*const (dyn FnOnce(()) + 'static)`, got `*const dyn for<'a> FnOnce(<u8 as Trait>::Gat<'a>)`
+   |
+note: previous use here
+  --> $DIR/normalize-hidden-types.rs:44:9
+   |
+LL |         None
+   |         ^^^^
 
 error: concrete type differs from previous defining opaque type use
   --> $DIR/normalize-hidden-types.rs:52:25
@@ -52,4 +48,3 @@ LL |         None
 
 error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/type-alias-impl-trait/self-referential-2.current.stderr b/tests/ui/type-alias-impl-trait/self-referential-2.current.stderr
diff --git a/tests/ui/type-alias-impl-trait/self-referential-2.rs b/tests/ui/type-alias-impl-trait/self-referential-2.rs
@@ -1,14 +1,14 @@
 //@ revisions: current next
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
-//@[next] check-pass
+//@ check-pass
 #![feature(type_alias_impl_trait)]
 
 type Foo = impl std::fmt::Debug;
 type Bar = impl PartialEq<Foo>;
 
 fn bar() -> Bar {
-    42_i32 //[current]~^ ERROR can't compare `i32` with `Foo`
+    42_i32
 }
 
 fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/self-referential-3.rs b/tests/ui/type-alias-impl-trait/self-referential-3.rs
@@ -5,7 +5,7 @@
 type Bar<'a, 'b> = impl PartialEq<Bar<'a, 'b>> + std::fmt::Debug;
 
 fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
-    //~^ ERROR can't compare `&i32` with `Bar<'a, 'b>`
+    //~^ ERROR overflow normalizing the type alias `Bar<'a, 'b>`
     i
 }
 
diff --git a/tests/ui/type-alias-impl-trait/self-referential-3.stderr b/tests/ui/type-alias-impl-trait/self-referential-3.stderr

Original file line number	Diff line number	Diff line change
`@@ -22,7 +22,7 @@ fn sum_to(n: u32) -> impl Foo {`
`22`	`22`	`0`
`23`	`23`	`} else {`
`24`	`24`	`n + sum_to(n - 1)`
`25`		- //~^ ERROR cannot add `impl Foo` to `u32`
	`25`	+ //~^ ERROR cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
`26`	`26`	`}`
`27`	`27`	`}`
`28`	`28`
`@@ -32,12 +32,15 @@ trait Leak: Sized {`
`32`	`32`	`}`
`33`	`33`	`impl<T> Leak for T {`
`34`	`34`	`default type T = ();`
`35`		`- default fn leak(self) -> Self::T { panic!() }`
	`35`	`+ default fn leak(self) -> Self::T {`
	`36`	`+ panic!()`
	`37`	`+ }`
`36`	`38`	`}`
`37`	`39`	`impl Leak for i32 {`
`38`	`40`	`type T = i32;`
`39`		`- fn leak(self) -> i32 { self }`
	`41`	`+ fn leak(self) -> i32 {`
	`42`	`+ self`
	`43`	`+ }`
`40`	`44`	`}`
`41`	`45`
`42`		`-fn main() {`
`43`		`-}`
	`46`	`+fn main() {}`
Original file line number	Diff line number	Diff line change
`@@ -11,7 +11,7 @@ impl PartialEq<(Bar, i32)> for Bar {`
`11`	`11`	`}`
`12`	`12`
`13`	`13`	`fn foo() -> Foo {`
`14`		- //~^ ERROR can't compare `Bar` with `(Foo, i32)`
	`14`	+ //~^ ERROR overflow evaluating the requirement `Bar: PartialEq<(Foo, i32)>`
`15`	`15`	`Bar`
`16`	`16`	`}`
`17`	`17`