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

This reverts commit ad00868.

Author: oli-obk

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2543,7 +2543,7 @@ 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()))
             })?;

tests/ui/auto-traits/opaque_type_candidate_selection.rs

@@ -0,0 +1,29 @@
+//! used to ICE: #119272
+
+#![feature(type_alias_impl_trait)]
+mod defining_scope {
+    use super::*;
+    pub type Alias<T> = impl Sized;
+
+    pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
+        x
+    }
+}
+
+struct Container<T: Trait<U>, U> {
+    x: <T as Trait<U>>::Assoc,
+}
+
+trait Trait<T> {
+    type Assoc;
+}
+
+impl<T> Trait<T> for T {
+    type Assoc = Box<u32>;
+}
+impl<T> Trait<T> for defining_scope::Alias<T> {
+    //~^ ERROR: conflicting implementations
+    type Assoc = usize;
+}
+
+fn main() {}

tests/ui/auto-traits/opaque_type_candidate_selection.stderr

@@ -0,0 +1,12 @@
+error[E0119]: conflicting implementations of trait `Trait<_>`
+  --> $DIR/opaque_type_candidate_selection.rs:24:1
+   |
+LL | impl<T> Trait<T> for T {
+   | ---------------------- first implementation here
+...
+LL | impl<T> Trait<T> for defining_scope::Alias<T> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/occurs-check/opaques.old.stderr

@@ -0,0 +1,21 @@
+error[E0284]: type annotations needed
+  --> $DIR/opaques.rs:12:20
+   |
+LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
+   |                    ^ cannot infer type
+   |
+   = note: cannot satisfy `<Alias<T> as Trait<T>>::Assoc == _`
+note: required because it appears within the type `Container<Alias<T>, T>`
+  --> $DIR/opaques.rs:18:8
+   |
+LL | struct Container<T: Trait<U>, U> {
+   |        ^^^^^^^^^
+   = help: unsized fn params are gated as an unstable feature
+help: function arguments must have a statically known size, borrowed types always have a known size
+   |
+LL |     pub fn cast<T>(x: &Container<Alias<T>, T>) -> Container<T, T> {
+   |                       +
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0284`.

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.current.stderr

@@ -1,5 +1,5 @@
 error[E0282]: type annotations needed for `&_`
-  --> $DIR/call_method_on_inherent_impl_on_rigid_type.rs:14:13
+  --> $DIR/call_method_on_inherent_impl_on_rigid_type.rs:15:13
    |
 LL |         let x = &my_foo();
    |             ^

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.next.stderr

@@ -1,5 +1,6 @@
 //@ revisions: current next
 //@[next] compile-flags: -Znext-solver
+//@[current] check-pass
 
 trait MyDebug {
     fn my_debug(&self);
@@ -14,7 +15,6 @@ fn my_foo() -> impl std::fmt::Debug {
         let x = &my_foo();
         //[next]~^ ERROR: type annotations needed
         x.my_debug();
-        //[current]~^ ERROR: no method named `my_debug`
     }
     ()
 }

tests/ui/impl-trait/call_method_on_inherent_impl_on_rigid_type.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`
     }
 }
 

tests/ui/impl-trait/equality.rs

@@ -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>`:
-             `&u32` implements `Add<u32>`
-             `&u32` implements `Add`
-             `u32` implements `Add<&u32>`
-             `u32` implements `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`.

tests/ui/impl-trait/equality.stderr

@@ -5,7 +5,7 @@ fn fine(x: impl Into<u32>) -> impl Into<u32> { x }
 
 fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
 //~^ ERROR nested `impl Trait` is not allowed
-//~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
+//~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfie
 
 fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
 //~^ ERROR nested `impl Trait` is not allowed
@@ -18,7 +18,7 @@ struct X;
 impl X {
     fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
     //~^ ERROR nested `impl Trait` is not allowed
-    //~| ERROR the trait bound `impl Debug: From<impl Into<u32>>` is not satisfied
+    //~| ERROR the trait bound `impl Into<u32>: Into<impl Debug>` is not satisfie
 }
 
 fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {