support non-defining uses in HIR typeck

20 files changed, 167 insertions, 177 deletions

diff --git a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.next.stderr b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.next.stderr
index d624fb1e42b..d6294efbd28 100644
--- a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.next.stderr
+++ b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.next.stderr
@@ -1,30 +1,14 @@
-error[E0283]: type annotations needed
-  --> $DIR/ambig-hr-projection-issue-93340.rs:17:5
+error[E0282]: type annotations needed
+  --> $DIR/ambig-hr-projection-issue-93340.rs:16:5
    |
 LL |     cmp_eq
    |     ^^^^^^ cannot infer type of the type parameter `A` declared on the function `cmp_eq`
    |
-   = note: cannot satisfy `_: Scalar`
-note: required by a bound in `cmp_eq`
-  --> $DIR/ambig-hr-projection-issue-93340.rs:10:22
-   |
-LL | fn cmp_eq<'a, 'b, A: Scalar, B: Scalar, O: Scalar>(a: A::RefType<'a>, b: B::RefType<'b>) -> O {
-   |                      ^^^^^^ required by this bound in `cmp_eq`
 help: consider specifying the generic arguments
    |
 LL |     cmp_eq::<A, B, O>
    |           +++++++++++
 
-error[E0277]: expected a `Fn(<A as Scalar>::RefType<'_>, <B as Scalar>::RefType<'_>)` closure, found `for<'a, 'b> fn(<O as Scalar>::RefType<'a>, <_ as Scalar>::RefType<'b>) -> O {cmp_eq::<O, _, O>}`
-  --> $DIR/ambig-hr-projection-issue-93340.rs:14:1
-   |
-LL | / fn build_expression<A: Scalar, B: Scalar, O: Scalar>(
-LL | | ) -> impl Fn(A::RefType<'_>, B::RefType<'_>) -> O {
-   | |_________________________________________________^ expected an `Fn(<A as Scalar>::RefType<'_>, <B as Scalar>::RefType<'_>)` closure, found `for<'a, 'b> fn(<O as Scalar>::RefType<'a>, <_ as Scalar>::RefType<'b>) -> O {cmp_eq::<O, _, O>}`
-   |
-   = help: the trait `for<'a, 'b> Fn(<A as Scalar>::RefType<'a>, <B as Scalar>::RefType<'b>)` is not implemented for fn item `for<'a, 'b> fn(<O as Scalar>::RefType<'a>, <_ as Scalar>::RefType<'b>) -> O {cmp_eq::<O, _, O>}`
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0283.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.old.stderr b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.old.stderr
index 4a293d44e0e..d913b2e91ca 100644
--- a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.old.stderr
+++ b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.old.stderr
@@ -1,5 +1,5 @@
 error[E0283]: type annotations needed
-  --> $DIR/ambig-hr-projection-issue-93340.rs:17:5
+  --> $DIR/ambig-hr-projection-issue-93340.rs:16:5
    |
 LL |     cmp_eq
    |     ^^^^^^ cannot infer type of the type parameter `A` declared on the function `cmp_eq`
diff --git a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.rs b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.rs
index 6ba3c4c65d0..acfebad38db 100644
--- a/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.rs
+++ b/tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.rs
@@ -13,7 +13,6 @@ fn cmp_eq<'a, 'b, A: Scalar, B: Scalar, O: Scalar>(a: A::RefType<'a>, b: B::RefT
 
 fn build_expression<A: Scalar, B: Scalar, O: Scalar>(
 ) -> impl Fn(A::RefType<'_>, B::RefType<'_>) -> O {
-    //[next]~^^ ERROR expected a `Fn(<A as Scalar>::RefType<'_>, <B as Scalar>::RefType<'_>)` closure
     cmp_eq
     //~^ ERROR type annotations needed
 }
diff --git a/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr b/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr
index 5caf0eb2fd4..7170efc8638 100644
--- a/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr
+++ b/tests/ui/impl-trait/auto-trait-selection-freeze.next.stderr
@@ -1,17 +1,9 @@
-error[E0283]: type annotations needed
+error[E0282]: type annotations needed
   --> $DIR/auto-trait-selection-freeze.rs:19:16
    |
 LL |     if false { is_trait(foo()) } else { Default::default() }
-   |                ^^^^^^^^ ----- type must be known at this point
-   |                |
-   |                cannot infer type of the type parameter `T` declared on the function `is_trait`
+   |                ^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `is_trait`
    |
-   = note: cannot satisfy `_: Trait<_>`
-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::<T, U>(foo()) } else { Default::default() }
@@ -19,4 +11,4 @@ LL |     if false { is_trait::<T, U>(foo()) } else { Default::default() }
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0283`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/impl-trait/auto-trait-selection.next.stderr b/tests/ui/impl-trait/auto-trait-selection.next.stderr
index d34fdcc4496..0f33aca3019 100644
--- a/tests/ui/impl-trait/auto-trait-selection.next.stderr
+++ b/tests/ui/impl-trait/auto-trait-selection.next.stderr
@@ -1,17 +1,9 @@
-error[E0283]: type annotations needed
+error[E0282]: type annotations needed
   --> $DIR/auto-trait-selection.rs:15:16
    |
 LL |     if false { is_trait(foo()) } else { Default::default() }
-   |                ^^^^^^^^ ----- type must be known at this point
-   |                |
-   |                cannot infer type of the type parameter `T` declared on the function `is_trait`
+   |                ^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `is_trait`
    |
-   = note: cannot satisfy `_: Trait<_>`
-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::<T, U>(foo()) } else { Default::default() }
@@ -19,4 +11,4 @@ LL |     if false { is_trait::<T, U>(foo()) } else { Default::default() }
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0283`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/impl-trait/recursive-in-exhaustiveness.current.stderr b/tests/ui/impl-trait/recursive-in-exhaustiveness.current.stderr
index 080c3284641..11a88b0918c 100644
--- a/tests/ui/impl-trait/recursive-in-exhaustiveness.current.stderr
+++ b/tests/ui/impl-trait/recursive-in-exhaustiveness.current.stderr
@@ -11,7 +11,7 @@ LL | fn build2<T>(x: T) -> impl Sized {
    |                       ^^^^^^^^^^
 
 error[E0720]: cannot resolve opaque type
-  --> $DIR/recursive-in-exhaustiveness.rs:39:23
+  --> $DIR/recursive-in-exhaustiveness.rs:37:23
    |
 LL | fn build3<T>(x: T) -> impl Sized {
    |                       ^^^^^^^^^^
diff --git a/tests/ui/impl-trait/recursive-in-exhaustiveness.next.stderr b/tests/ui/impl-trait/recursive-in-exhaustiveness.next.stderr
index db57be73acc..45df8cc9c0c 100644
--- a/tests/ui/impl-trait/recursive-in-exhaustiveness.next.stderr
+++ b/tests/ui/impl-trait/recursive-in-exhaustiveness.next.stderr
@@ -1,80 +1,21 @@
-error[E0284]: type annotations needed: cannot normalize `build<_>::{opaque#0}`
-  --> $DIR/recursive-in-exhaustiveness.rs:20:5
+error[E0282]: type annotations needed
+  --> $DIR/recursive-in-exhaustiveness.rs:19:17
    |
-LL |     build(x)
-   |     ^^^^^^^^ cannot normalize `build<_>::{opaque#0}`
+LL |     let (x,) = (build(x),);
+   |                 ^^^^^^^^ cannot infer type
 
-error[E0271]: type mismatch resolving `build2<(_,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:30:6
+error[E0282]: type annotations needed
+  --> $DIR/recursive-in-exhaustiveness.rs:29:17
    |
-LL |     (build2(x),)
-   |      ^^^^^^^^^ types differ
+LL |     let (x,) = (build2(x),);
+   |                 ^^^^^^^^^ cannot infer type
 
-error[E0271]: type mismatch resolving `build2<(_,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:30:5
+error[E0282]: type annotations needed
+  --> $DIR/recursive-in-exhaustiveness.rs:40:5
    |
-LL |     (build2(x),)
-   |     ^^^^^^^^^^^^ types differ
+LL |     build3(x)
+   |     ^^^^^^^^^ cannot infer type
 
-error[E0277]: the size for values of type `(impl Sized,)` cannot be known at compilation time
-  --> $DIR/recursive-in-exhaustiveness.rs:30:5
-   |
-LL |     (build2(x),)
-   |     ^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `(impl Sized,)`
-   = note: tuples must have a statically known size to be initialized
-
-error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:41:17
-   |
-LL |     let (x,) = (build3((x,)),);
-   |                 ^^^^^^^^^^^^ types differ
-
-error[E0277]: the size for values of type `(impl Sized,)` cannot be known at compilation time
-  --> $DIR/recursive-in-exhaustiveness.rs:41:16
-   |
-LL |     let (x,) = (build3((x,)),);
-   |                ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `(impl Sized,)`
-   = note: tuples must have a statically known size to be initialized
-
-error[E0308]: mismatched types
-  --> $DIR/recursive-in-exhaustiveness.rs:41:16
-   |
-LL | fn build3<T>(x: T) -> impl Sized {
-   |                       ---------- the found opaque type
-LL |
-LL |     let (x,) = (build3((x,)),);
-   |                ^^^^^^^^^^^^^^^ types differ
-   |
-   = note: expected type `_`
-             found tuple `(impl Sized,)`
-
-error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:41:17
-   |
-LL |     let (x,) = (build3((x,)),);
-   |                 ^^^^^^^^^^^^ types differ
-   |
-   = note: the return type of a function must have a statically known size
-
-error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:41:16
-   |
-LL |     let (x,) = (build3((x,)),);
-   |                ^^^^^^^^^^^^^^^ types differ
-
-error[E0271]: type mismatch resolving `build3<(T,)>::{opaque#0} normalizes-to _`
-  --> $DIR/recursive-in-exhaustiveness.rs:41:17
-   |
-LL |     let (x,) = (build3((x,)),);
-   |                 ^^^^^^^^^^^^ types differ
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 10 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0271, E0277, E0284, E0308.
-For more information about an error, try `rustc --explain E0271`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/impl-trait/recursive-in-exhaustiveness.rs b/tests/ui/impl-trait/recursive-in-exhaustiveness.rs
index dabef22af86..7aee8a630a5 100644
--- a/tests/ui/impl-trait/recursive-in-exhaustiveness.rs
+++ b/tests/ui/impl-trait/recursive-in-exhaustiveness.rs
@@ -17,8 +17,8 @@
 fn build<T>(x: T) -> impl Sized {
     //[current]~^ ERROR cannot resolve opaque type
     let (x,) = (build(x),);
+    //[next]~^ ERROR type annotations needed
     build(x)
-    //[next]~^ ERROR type annotations needed: cannot normalize `build<_>::{opaque#0}`
 }
 
 // Opaque<T> = (Opaque<T>,)
@@ -27,10 +27,8 @@ fn build<T>(x: T) -> impl Sized {
 fn build2<T>(x: T) -> impl Sized {
     //[current]~^ ERROR cannot resolve opaque type
     let (x,) = (build2(x),);
+    //[next]~^ ERROR type annotations needed
     (build2(x),)
-    //[next]~^ ERROR type mismatch resolving
-    //[next]~| ERROR type mismatch resolving
-    //[next]~| ERROR the size for values of type
 }
 
 // Opaque<T> = Opaque<(T,)>
@@ -39,13 +37,8 @@ fn build2<T>(x: T) -> impl Sized {
 fn build3<T>(x: T) -> impl Sized {
     //[current]~^ ERROR cannot resolve opaque type
     let (x,) = (build3((x,)),);
-    //[next]~^ ERROR type mismatch resolving
-    //[next]~| ERROR type mismatch resolving
-    //[next]~| ERROR type mismatch resolving
-    //[next]~| ERROR type mismatch resolving
-    //[next]~| ERROR the size for values of type
-    //[next]~| ERROR mismatched types
     build3(x)
+    //[next]~^ ERROR type annotations needed
 }
 
 fn main() {}
diff --git a/tests/ui/impl-trait/two_tait_defining_each_other2.next.stderr b/tests/ui/impl-trait/two_tait_defining_each_other2.next.stderr
index fac4776905d..785e5fdeb64 100644
--- a/tests/ui/impl-trait/two_tait_defining_each_other2.next.stderr
+++ b/tests/ui/impl-trait/two_tait_defining_each_other2.next.stderr
@@ -1,9 +1,15 @@
 error[E0282]: type annotations needed
-  --> $DIR/two_tait_defining_each_other2.rs:12:11
+  --> $DIR/two_tait_defining_each_other2.rs:12:8
    |
 LL | fn muh(x: A) -> B {
-   |           ^ cannot infer type
+   |        ^ cannot infer type
 
-error: aborting due to 1 previous error
+error[E0282]: type annotations needed
+  --> $DIR/two_tait_defining_each_other2.rs:14:5
+   |
+LL |     x // B's hidden type is A (opaquely)
+   |     ^ cannot infer type
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/impl-trait/two_tait_defining_each_other2.rs b/tests/ui/impl-trait/two_tait_defining_each_other2.rs
index ec2963249f9..99262f4bc4b 100644
--- a/tests/ui/impl-trait/two_tait_defining_each_other2.rs
+++ b/tests/ui/impl-trait/two_tait_defining_each_other2.rs
@@ -12,7 +12,8 @@ trait Foo {}
 fn muh(x: A) -> B {
     //[next]~^ ERROR: type annotations needed
     x // B's hidden type is A (opaquely)
-    //[current]~^ ERROR opaque type's hidden type cannot be another opaque type
+    //[next]~^ ERROR: type annotations needed
+    //[current]~^^ ERROR opaque type's hidden type cannot be another opaque type
 }
 
 struct Bar;
diff --git a/tests/ui/traits/next-solver/opaques/different-bound-vars.current.stderr b/tests/ui/traits/next-solver/opaques/different-bound-vars.current.stderr
new file mode 100644
index 00000000000..32e92e46a88
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/different-bound-vars.current.stderr
@@ -0,0 +1,14 @@
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/different-bound-vars.rs:13:37
+   |
+LL |         let _: for<'b> fn(&'b ()) = foo::<U, T>(false);
+   |                                     ^^^^^^^^^^^^^^^^^^ expected `for<'a> fn(&'a ())`, got `for<'b> fn(&'b ())`
+   |
+note: previous use here
+  --> $DIR/different-bound-vars.rs:12:37
+   |
+LL |         let _: for<'a> fn(&'a ()) = foo::<T, U>(false);
+   |                                     ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/traits/next-solver/opaques/different-bound-vars.rs b/tests/ui/traits/next-solver/opaques/different-bound-vars.rs
new file mode 100644
index 00000000000..5801a5edeb4
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/different-bound-vars.rs
@@ -0,0 +1,20 @@
+// Check whether we support defining uses with different bound vars.
+// This needs to handle both mismatches for the same opaque type storage
+// entry, but also between different entries.
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+fn foo<T, U>(b: bool) -> impl Sized {
+    if b {
+        let _: for<'a> fn(&'a ()) = foo::<T, U>(false);
+        let _: for<'b> fn(&'b ()) = foo::<U, T>(false);
+        //[current]~^ ERROR concrete type differs from previous defining opaque type use
+    }
+
+    (|&()| ()) as for<'c> fn(&'c ())
+}
+
+fn main() {}
diff --git a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.is_send.stderr b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.is_send.stderr
index 6d2bbd8b08b..a188629a475 100644
--- a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.is_send.stderr
+++ b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.is_send.stderr
@@ -1,16 +1,9 @@
-error[E0283]: type annotations needed: cannot satisfy `Foo: Send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:16:18
+error[E0282]: type annotations needed
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:15:12
    |
-LL |     needs_send::<Foo>();
-   |                  ^^^
-   |
-   = note: cannot satisfy `Foo: Send`
-note: required by a bound in `needs_send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:12:18
-   |
-LL | fn needs_send<T: Send>() {}
-   |                  ^^^^ required by this bound in `needs_send`
+LL | fn test(_: Foo) {
+   |            ^^^ cannot infer type
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0283`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.not_send.stderr b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.not_send.stderr
index 6d2bbd8b08b..a188629a475 100644
--- a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.not_send.stderr
+++ b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.not_send.stderr
@@ -1,16 +1,9 @@
-error[E0283]: type annotations needed: cannot satisfy `Foo: Send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:16:18
+error[E0282]: type annotations needed
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:15:12
    |
-LL |     needs_send::<Foo>();
-   |                  ^^^
-   |
-   = note: cannot satisfy `Foo: Send`
-note: required by a bound in `needs_send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:12:18
-   |
-LL | fn needs_send<T: Send>() {}
-   |                  ^^^^ required by this bound in `needs_send`
+LL | fn test(_: Foo) {
+   |            ^^^ cannot infer type
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0283`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.rs b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.rs
index fddf892e1ef..8ff99d32f06 100644
--- a/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.rs
+++ b/tests/ui/traits/next-solver/opaques/dont-type_of-tait-in-defining-scope.rs
@@ -13,8 +13,8 @@ fn needs_send<T: Send>() {}
 
 #[define_opaque(Foo)]
 fn test(_: Foo) {
-    needs_send::<Foo>();
     //~^ ERROR type annotations needed
+    needs_send::<Foo>();
 }
 
 #[define_opaque(Foo)]
diff --git a/tests/ui/traits/next-solver/opaques/non-defining-use-hir-typeck.rs b/tests/ui/traits/next-solver/opaques/non-defining-use-hir-typeck.rs
new file mode 100644
index 00000000000..a55be5fde9e
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/non-defining-use-hir-typeck.rs
@@ -0,0 +1,28 @@
+//@ ignore-compare-mode-next-solver
+//@ compile-flags: -Znext-solver
+//@ check-pass
+#![feature(type_alias_impl_trait)]
+
+// Make sure that we support non-defining uses in HIR typeck.
+// Regression test for trait-system-refactor-initiative#135.
+
+fn non_defining_recurse<T>(b: bool) -> impl Sized {
+    if b {
+        // This results in an opaque type use `opaque<()> = ?unconstrained`
+        // during HIR typeck.
+        non_defining_recurse::<()>(false);
+    }
+}
+
+trait Eq<T, U> {}
+impl<T> Eq<T, T> for () {}
+fn is_eq<T: Eq<U, V>, U, V>() {}
+type Tait<T> = impl Sized;
+#[define_opaque(Tait)]
+fn non_defining_explicit<T>() {
+    is_eq::<(), Tait<_>, u32>(); // constrains opaque type args via hidden type
+    is_eq::<(), Tait<u64>, _>(); // constraints hidden type via args
+    is_eq::<(), Tait<T>, T>(); // actually defines
+}
+
+fn main() {}
diff --git a/tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs b/tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs
new file mode 100644
index 00000000000..5e7e9738616
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs
@@ -0,0 +1,16 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// The recursive call to `foo` results in the opaque type use `opaque<U, T> = ?unconstrained`.
+// This needs to be supported and treated as a revealing use.
+
+fn foo<T, U>(b: bool) -> impl Sized {
+    if b {
+        foo::<U, T>(b);
+    }
+    1u16
+}
+
+fn main() {}
diff --git a/tests/ui/type-alias-impl-trait/constrain_in_projection2.next.stderr b/tests/ui/type-alias-impl-trait/constrain_in_projection2.next.stderr
index 72a253c4be8..b50d1b60c43 100644
--- a/tests/ui/type-alias-impl-trait/constrain_in_projection2.next.stderr
+++ b/tests/ui/type-alias-impl-trait/constrain_in_projection2.next.stderr
@@ -1,24 +1,9 @@
-error[E0283]: type annotations needed: cannot satisfy `Foo: Trait<Bar>`
-  --> $DIR/constrain_in_projection2.rs:28:14
+error[E0282]: type annotations needed
+  --> $DIR/constrain_in_projection2.rs:28:13
    |
 LL |     let x = <Foo as Trait<Bar>>::Assoc::default();
-   |              ^^^
-   |
-note: multiple `impl`s satisfying `Foo: Trait<Bar>` found
-  --> $DIR/constrain_in_projection2.rs:18:1
-   |
-LL | impl Trait<()> for Foo {
-   | ^^^^^^^^^^^^^^^^^^^^^^
-...
-LL | impl Trait<u32> for Foo {
-   | ^^^^^^^^^^^^^^^^^^^^^^^
-   = note: associated types cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
-help: use the fully qualified path to an implementation
-   |
-LL -     let x = <Foo as Trait<Bar>>::Assoc::default();
-LL +     let x = <<Type as Trait>::Assoc as Trait<Bar>>::Assoc::default();
-   |
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0283`.
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/type-alias-impl-trait/constrain_in_projection2.rs b/tests/ui/type-alias-impl-trait/constrain_in_projection2.rs
index 61773cf59d4..c4aa6f32eab 100644
--- a/tests/ui/type-alias-impl-trait/constrain_in_projection2.rs
+++ b/tests/ui/type-alias-impl-trait/constrain_in_projection2.rs
@@ -26,7 +26,7 @@ impl Trait<u32> for Foo {
 #[define_opaque(Bar)]
 fn bop() {
     let x = <Foo as Trait<Bar>>::Assoc::default();
-    //[next]~^ ERROR: cannot satisfy `Foo: Trait<Bar>`
+    //[next]~^ ERROR: type annotations needed
     //[current]~^^ ERROR: `Foo: Trait<Bar>` is not satisfied
     //[current]~| ERROR: `Foo: Trait<Bar>` is not satisfied
 }
diff --git a/tests/ui/type-alias-impl-trait/normalize-args-before-defining-use-check.rs b/tests/ui/type-alias-impl-trait/normalize-args-before-defining-use-check.rs
new file mode 100644
index 00000000000..2879b8fe94c
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/normalize-args-before-defining-use-check.rs
@@ -0,0 +1,33 @@
+#![feature(type_alias_impl_trait)]
+
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ [next] compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#49.
+
+trait Mirror<'a> {
+    type Assoc;
+}
+impl<'a, T> Mirror<'a> for T {
+    type Assoc = T;
+}
+
+type HrAmbigAlias<T> = impl Sized;
+fn ret_tait<T>() -> for<'a> fn(HrAmbigAlias<<T as Mirror<'a>>::Assoc>) {
+    |_| ()
+}
+
+#[define_opaque(HrAmbigAlias)]
+fn define_hr_ambig_alias<T>() {
+    let _: fn(T) = ret_tait::<T>();
+}
+
+type InUserType<T> = impl Sized;
+#[define_opaque(InUserType)]
+fn in_user_type<T>() {
+    let x: InUserType<<T as Mirror<'static>>::Assoc> = ();
+}
+
+fn main() {}