Auto merge of #145993 - lcnr:allow-calling-opaques, r=BoxyUwU

`-Znext-solver` allow `ExprKind::Call` for not-yet defined opaques

Based on https://github.com/rust-lang/rust/pull/146329. Revival of rust-lang/rust#140496. See the comment on `OpaqueTypesJank`. I've used the following document while working on this https://hackmd.io/Js61f8PRTcyaiyqS-fH9iQ.

Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/181. It does introduce one subtle footgun we may want to handle before stabilization, opened https://github.com/rust-lang/trait-system-refactor-initiative/issues/230 for that. Also cc https://github.com/rust-lang/trait-system-refactor-initiative/issues/231 for deref and index operations

r? `@BoxyUwU`

19 files changed, 542 insertions, 28 deletions

diff --git a/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.current.stderr b/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.current.stderr
new file mode 100644
index 00000000000..c54c1bba028
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.current.stderr
@@ -0,0 +1,62 @@
+error[E0369]: cannot add `{integer}` to `impl Sized`
+  --> $DIR/ambiguous-ops.rs:17:15
+   |
+LL |         add() + 1
+   |         ----- ^ - {integer}
+   |         |
+   |         impl Sized
+
+error[E0368]: binary assignment operation `*=` cannot be applied to type `impl Sized`
+  --> $DIR/ambiguous-ops.rs:31:9
+   |
+LL |         temp *= 2;
+   |         ----^^^^^
+   |         |
+   |         cannot use `*=` on type `impl Sized`
+
+error[E0614]: type `DerefWrapper<impl Sized>` cannot be dereferenced
+  --> $DIR/ambiguous-ops.rs:57:22
+   |
+LL |         let _rarw = &*explicit_deref();
+   |                      ^^^^^^^^^^^^^^^^^ can't be dereferenced
+
+error[E0614]: type `DerefWrapper<impl Sized>` cannot be dereferenced
+  --> $DIR/ambiguous-ops.rs:69:9
+   |
+LL |         *explicit_deref_mut() = 1;
+   |         ^^^^^^^^^^^^^^^^^^^^^ can't be dereferenced
+
+error[E0277]: the type `impl Sized` cannot be indexed by `_`
+  --> $DIR/ambiguous-ops.rs:94:18
+   |
+LL |         let _y = explicit_index()[0];
+   |                  ^^^^^^^^^^^^^^^^ `impl Sized` cannot be indexed by `_`
+   |
+   = help: the trait `Index<_>` is not implemented for `impl Sized`
+note: required for `IndexWrapper<impl Sized>` to implement `Index<_>`
+  --> $DIR/ambiguous-ops.rs:81:22
+   |
+LL | impl<T: Index<U>, U> Index<U> for IndexWrapper<T> {
+   |         --------     ^^^^^^^^     ^^^^^^^^^^^^^^^
+   |         |
+   |         unsatisfied trait bound introduced here
+
+error[E0277]: the type `impl Sized` cannot be indexed by `_`
+  --> $DIR/ambiguous-ops.rs:106:9
+   |
+LL |         explicit_index_mut()[0] = 1;
+   |         ^^^^^^^^^^^^^^^^^^^^ `impl Sized` cannot be indexed by `_`
+   |
+   = help: the trait `Index<_>` is not implemented for `impl Sized`
+note: required for `IndexWrapper<impl Sized>` to implement `Index<_>`
+  --> $DIR/ambiguous-ops.rs:81:22
+   |
+LL | impl<T: Index<U>, U> Index<U> for IndexWrapper<T> {
+   |         --------     ^^^^^^^^     ^^^^^^^^^^^^^^^
+   |         |
+   |         unsatisfied trait bound introduced here
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0277, E0368, E0369, E0614.
+For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.rs b/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.rs
new file mode 100644
index 00000000000..0aa5715339d
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/ambiguous-ops.rs
@@ -0,0 +1,117 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] check-pass
+
+// Make sure we support non-call operations for opaque types even if
+// its not part of its item bounds.
+
+use std::ops::{Deref, DerefMut, Index, IndexMut};
+
+fn mk<T>() -> T {
+    todo!()
+}
+
+fn add() -> impl Sized {
+    let unconstrained = if false {
+        add() + 1
+        //[current]~^ ERROR cannot add `{integer}` to `impl Sized
+    } else {
+        let with_infer = mk();
+        let _ = with_infer + 1;
+        with_infer
+    };
+    let _: u32 = unconstrained;
+    1u32
+}
+
+fn mul_assign() -> impl Sized {
+    if false {
+        let mut temp = mul_assign();
+        temp *= 2;
+        //[current]~^ ERROR binary assignment operation `*=` cannot be applied to type `impl Sized`
+    }
+
+    let mut with_infer = mk();
+    with_infer *= 2;
+    let _: u32 = with_infer;
+
+    1u32
+}
+
+struct DerefWrapper<T>(T);
+impl<T: Deref> Deref for DerefWrapper<T> {
+    type Target = T::Target;
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}
+impl<T: DerefMut> DerefMut for DerefWrapper<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut *self.0
+    }
+}
+
+fn explicit_deref() -> DerefWrapper<impl Sized> {
+    if false {
+        let _rarw = &*explicit_deref();
+        //[current]~^ ERROR type `DerefWrapper<impl Sized>` cannot be dereferenced
+
+        let mut with_infer = DerefWrapper(mk());
+        let _rarw = &*with_infer;
+        with_infer
+    } else {
+        DerefWrapper(&1u32)
+    }
+}
+fn explicit_deref_mut() -> DerefWrapper<impl Sized> {
+    if false {
+        *explicit_deref_mut() = 1;
+        //[current]~^ ERROR type `DerefWrapper<impl Sized>` cannot be dereferenced
+
+        let mut with_infer = DerefWrapper(Default::default());
+        *with_infer = 1;
+        with_infer
+    } else {
+        DerefWrapper(Box::new(1u32))
+    }
+}
+
+struct IndexWrapper<T>(T);
+impl<T: Index<U>, U> Index<U> for IndexWrapper<T> {
+    type Output = T::Output;
+    fn index(&self, index: U) -> &Self::Output {
+        &self.0[index]
+    }
+}
+impl<T: IndexMut<U>, U> IndexMut<U> for IndexWrapper<T> {
+    fn index_mut(&mut self, index: U) -> &mut Self::Output {
+        &mut self.0[index]
+    }
+}
+fn explicit_index() -> IndexWrapper<impl Sized> {
+    if false {
+        let _y = explicit_index()[0];
+        //[current]~^ ERROR the type `impl Sized` cannot be indexed by `_`
+
+        let with_infer = IndexWrapper(Default::default());
+        let _y = with_infer[0];
+        with_infer
+    } else {
+        IndexWrapper([1u32])
+    }
+}
+fn explicit_index_mut() -> IndexWrapper<impl Sized> {
+    if false {
+        explicit_index_mut()[0] = 1;
+        //[current]~^ ERROR the type `impl Sized` cannot be indexed by `_`
+
+        let mut with_infer = IndexWrapper(Default::default());
+        with_infer[0] = 1;
+        with_infer
+    } else {
+        IndexWrapper([1u32])
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.current.stderr b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.current.stderr
new file mode 100644
index 00000000000..e213dab5d96
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.current.stderr
@@ -0,0 +1,53 @@
+error[E0382]: use of moved value: `var`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:14:9
+   |
+LL |         let mut var = item_bound_is_too_weak();
+   |             ------- move occurs because `var` has type `impl FnOnce()`, which does not implement the `Copy` trait
+LL |         var();
+   |         ----- `var` moved due to this call
+LL |         var();
+   |         ^^^ value used here after move
+   |
+note: this value implements `FnOnce`, which causes it to be moved when called
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:13:9
+   |
+LL |         var();
+   |         ^^^
+
+error[E0618]: expected function, found `impl Sized`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:24:9
+   |
+LL | fn opaque_type_no_impl_fn() -> impl Sized {
+   | ----------------------------------------- `opaque_type_no_impl_fn` defined here returns `impl Sized`
+LL |     if false {
+LL |         opaque_type_no_impl_fn()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error[E0618]: expected function, found `impl Sized`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:34:9
+   |
+LL | fn opaque_type_no_impl_fn_incorrect() -> impl Sized {
+   | --------------------------------------------------- `opaque_type_no_impl_fn_incorrect` defined here returns `impl Sized`
+LL |     if false {
+LL |         opaque_type_no_impl_fn_incorrect()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error[E0618]: expected function, found `impl Deref<Target = impl Sized>`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:44:9
+   |
+LL | fn opaque_type_deref_no_impl_fn() -> impl Deref<Target = impl Sized> {
+   | -------------------------------------------------------------------- `opaque_type_deref_no_impl_fn` defined here returns `impl Deref<Target = impl Sized>`
+LL |     if false {
+LL |         opaque_type_deref_no_impl_fn()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0382, E0618.
+For more information about an error, try `rustc --explain E0382`.
diff --git a/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.next.stderr b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.next.stderr
new file mode 100644
index 00000000000..5678349cad3
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.next.stderr
@@ -0,0 +1,57 @@
+error[E0382]: use of moved value: `var`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:14:9
+   |
+LL |         let mut var = item_bound_is_too_weak();
+   |             ------- move occurs because `var` has type `{closure@$DIR/call-expr-incorrect-choice-diagnostics.rs:19:5: 19:12}`, which does not implement the `Copy` trait
+LL |         var();
+   |         ----- `var` moved due to this call
+LL |         var();
+   |         ^^^ value used here after move
+   |
+note: this value implements `FnOnce`, which causes it to be moved when called
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:13:9
+   |
+LL |         var();
+   |         ^^^
+help: consider cloning the value if the performance cost is acceptable
+   |
+LL |         var.clone()();
+   |            ++++++++
+
+error[E0618]: expected function, found `_`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:24:9
+   |
+LL | fn opaque_type_no_impl_fn() -> impl Sized {
+   | ----------------------------------------- `opaque_type_no_impl_fn` defined here returns `_`
+LL |     if false {
+LL |         opaque_type_no_impl_fn()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error[E0618]: expected function, found `_`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:34:9
+   |
+LL | fn opaque_type_no_impl_fn_incorrect() -> impl Sized {
+   | --------------------------------------------------- `opaque_type_no_impl_fn_incorrect` defined here returns `_`
+LL |     if false {
+LL |         opaque_type_no_impl_fn_incorrect()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error[E0618]: expected function, found `_`
+  --> $DIR/call-expr-incorrect-choice-diagnostics.rs:44:9
+   |
+LL | fn opaque_type_deref_no_impl_fn() -> impl Deref<Target = impl Sized> {
+   | -------------------------------------------------------------------- `opaque_type_deref_no_impl_fn` defined here returns `_`
+LL |     if false {
+LL |         opaque_type_deref_no_impl_fn()();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^--
+   |         |
+   |         call expression requires function
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0382, E0618.
+For more information about an error, try `rustc --explain E0382`.
diff --git a/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.rs b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.rs
new file mode 100644
index 00000000000..1d73985f78a
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/call-expr-incorrect-choice-diagnostics.rs
@@ -0,0 +1,52 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+
+// Testing the errors in case we've made a wrong choice when
+// calling an opaque.
+
+use std::ops::Deref;
+
+fn item_bound_is_too_weak() -> impl FnOnce() {
+    if false {
+        let mut var = item_bound_is_too_weak();
+        var();
+        var();
+        //~^ ERROR use of moved value: `var`
+    }
+
+    let mut state = String::new();
+    move || state.push('a')
+}
+
+fn opaque_type_no_impl_fn() -> impl Sized {
+    if false {
+        opaque_type_no_impl_fn()();
+        //[current]~^ ERROR expected function, found `impl Sized`
+        //[next]~^^ ERROR expected function, found `_`
+    }
+
+    1
+}
+
+fn opaque_type_no_impl_fn_incorrect() -> impl Sized {
+    if false {
+        opaque_type_no_impl_fn_incorrect()();
+        //[current]~^ ERROR expected function, found `impl Sized`
+        //[next]~^^ ERROR expected function, found `_`
+    }
+
+    || ()
+}
+
+fn opaque_type_deref_no_impl_fn() -> impl Deref<Target = impl Sized> {
+    if false {
+        opaque_type_deref_no_impl_fn()();
+        //[current]~^ ERROR expected function, found `impl Deref<Target = impl Sized>`
+        //[next]~^^ ERROR expected function, found `_`
+    }
+
+    &1
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.current.stderr b/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.current.stderr
new file mode 100644
index 00000000000..bbe90e5873d
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.current.stderr
@@ -0,0 +1,16 @@
+error[E0599]: no method named `len` found for struct `Wrapper<T>` in the current scope
+  --> $DIR/deref-constrains-self-ty.rs:22:32
+   |
+LL | struct Wrapper<T>(T);
+   | ----------------- method `len` not found for this struct
+...
+LL |         let _ = Wrapper(foo()).len();
+   |                                ^^^ method not found in `Wrapper<impl Sized>`
+   |
+   = help: items from traits can only be used if the trait is implemented and in scope
+   = note: the following trait defines an item `len`, perhaps you need to implement it:
+           candidate #1: `ExactSizeIterator`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0599`.
diff --git a/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.rs b/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.rs
new file mode 100644
index 00000000000..d143878bc74
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/deref-constrains-self-ty.rs
@@ -0,0 +1,28 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] check-pass
+
+// A test which shows that autoderef can constrain opaque types even
+// though it's supposed to treat not-yet-defined opaque types as
+// mostly rigid. I don't think this should necessarily compile :shrug:
+use std::ops::Deref;
+
+struct Wrapper<T>(T);
+
+impl<T> Deref for Wrapper<Vec<T>> {
+    type Target = Vec<T>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+fn foo() -> impl Sized {
+    if false {
+        let _ = Wrapper(foo()).len();
+        //[current]~^ ERROR no method named `len` found for struct `Wrapper<T>` in the current scope
+    }
+
+    std::iter::once(1).collect()
+}
+fn main() {}
diff --git a/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.current.stderr b/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.current.stderr
index 30424ec58f9..bac5b3e0cf4 100644
--- a/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.current.stderr
+++ b/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.current.stderr
@@ -1,5 +1,5 @@
 error[E0792]: expected generic type parameter, found `impl Foo`
-  --> $DIR/double-wrap-with-defining-use.rs:12:26
+  --> $DIR/double-wrap-with-defining-use.rs:11:26
    |
 LL | fn a<T: Foo>(x: T) -> impl Foo {
    |      - this generic parameter must be used with a generic type parameter
@@ -7,7 +7,7 @@ LL |     if true { x } else { a(a(x)) }
    |                          ^^^^^^^
 
 error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
-  --> $DIR/double-wrap-with-defining-use.rs:12:26
+  --> $DIR/double-wrap-with-defining-use.rs:11:26
    |
 LL |     if true { x } else { a(a(x)) }
    |                          ^^^^^^^
diff --git a/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.rs b/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.rs
index 734b1920772..39b327eff18 100644
--- a/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.rs
+++ b/tests/ui/impl-trait/non-defining-uses/double-wrap-with-defining-use.rs
@@ -1,7 +1,6 @@
 // Regression test for ICE from issue #140545
 // The error message is confusing and wrong, but that's a different problem (#139350)
 
-//@ edition:2018
 //@ revisions: current next
 //@[next] compile-flags: -Znext-solver
 //@ ignore-compare-mode-next-solver (explicit revisions)
diff --git a/tests/ui/impl-trait/non-defining-uses/function-call-on-infer.rs b/tests/ui/impl-trait/non-defining-uses/function-call-on-infer.rs
new file mode 100644
index 00000000000..9b9156ee4c7
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/function-call-on-infer.rs
@@ -0,0 +1,73 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#181. Make sure calling
+// opaque types works.
+
+fn fn_trait() -> impl Fn() {
+    if false {
+        let f = fn_trait();
+        f();
+    }
+
+    || ()
+}
+
+fn fn_trait_ref() -> impl Fn() {
+    if false {
+        let f = &fn_trait();
+        f();
+    }
+    || ()
+}
+
+fn fn_mut() -> impl FnMut() -> usize {
+    if false {
+        let mut f = fn_mut();
+        f();
+    }
+
+    let mut state = 0;
+    move || {
+        state += 1;
+        state
+    }
+}
+
+fn fn_mut_ref() -> impl FnMut() -> usize {
+    if false {
+        let mut f = &mut fn_mut();
+        f();
+    }
+
+    let mut state = 0;
+    move || {
+        state += 1;
+        state
+    }
+}
+
+
+fn fn_once() -> impl FnOnce() {
+    if false {
+        let mut f = fn_once();
+        f();
+    }
+
+    let string = String::new();
+    move || drop(string)
+}
+
+fn fn_once_ref() -> impl FnOnce() {
+    if false {
+        let mut f = Box::new(fn_once_ref());
+        f();
+    }
+
+    let string = String::new();
+    move || drop(string)
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.current.stderr b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.current.stderr
index ccbe2d3593c..5dc66f45465 100644
--- a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.current.stderr
+++ b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.current.stderr
@@ -5,7 +5,7 @@ LL | fn create_complex_future() -> impl Future<Output = impl ReturnsSend> {
    |                                                    ^^^^^^^^^^^^^^^^ the trait `ReturnsSend` is not implemented for `()`
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/ice-issue-146191.rs:14:1
+  --> $DIR/ice-issue-146191.rs:13:1
    |
 LL | trait ReturnsSend {}
    | ^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.next.stderr b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.next.stderr
index e8b551c65fc..4a88359ca96 100644
--- a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.next.stderr
+++ b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.next.stderr
@@ -4,14 +4,6 @@ error[E0282]: type annotations needed
 LL |     async { create_complex_future().await }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
 
-error[E0282]: type annotations needed
-  --> $DIR/ice-issue-146191.rs:8:5
-   |
-LL |     async { create_complex_future().await }
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.rs b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.rs
index 356f7d01eb9..84f139da4e3 100644
--- a/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.rs
+++ b/tests/ui/impl-trait/non-defining-uses/ice-issue-146191.rs
@@ -8,7 +8,6 @@ fn create_complex_future() -> impl Future<Output = impl ReturnsSend> {
     async { create_complex_future().await }
     //[current]~^ ERROR recursion in an async block requires
     //[next]~^^ ERROR type annotations needed
-    //[next]~| ERROR type annotations needed
 }
 
 trait ReturnsSend {}
diff --git a/tests/ui/impl-trait/non-defining-uses/impl-deref-function-call.rs b/tests/ui/impl-trait/non-defining-uses/impl-deref-function-call.rs
new file mode 100644
index 00000000000..5ff0dae55cc
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/impl-deref-function-call.rs
@@ -0,0 +1,56 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#181. We want to
+// be able to step through `impl Deref` in its defining scope.
+use std::ops::{Deref, DerefMut};
+fn impl_deref_fn() -> impl Deref<Target = fn(fn(&str) -> usize)> {
+    if false {
+        let func = impl_deref_fn();
+        func(|s| s.len());
+    }
+
+    &((|_| ()) as fn(_))
+}
+
+fn impl_deref_impl_fn() -> impl Deref<Target = impl Fn()> {
+    if false {
+        let func = impl_deref_impl_fn();
+        func();
+    }
+
+    &|| ()
+}
+
+fn impl_deref_impl_deref_impl_fn() -> impl Deref<Target = impl Deref<Target = impl Fn()>> {
+    if false {
+        let func = impl_deref_impl_deref_impl_fn();
+        func();
+    }
+
+    &&|| ()
+}
+
+
+fn impl_deref_mut_impl_fn() -> impl DerefMut<Target = impl Fn()> {
+    if false {
+        let func = impl_deref_impl_fn();
+        func();
+    }
+
+    Box::new(|| ())
+}
+
+
+fn impl_deref_mut_impl_fn_mut() -> impl DerefMut<Target = impl FnMut()> {
+    if false {
+        let mut func = impl_deref_mut_impl_fn_mut();
+        func();
+    }
+
+    let mut state = 0;
+    Box::new(move || state += 1)
+}
+fn main() {}
diff --git a/tests/ui/impl-trait/non-defining-uses/shex_compat-regression-test.rs b/tests/ui/impl-trait/non-defining-uses/shex_compat-regression-test.rs
new file mode 100644
index 00000000000..aa1b51d6906
--- /dev/null
+++ b/tests/ui/impl-trait/non-defining-uses/shex_compat-regression-test.rs
@@ -0,0 +1,19 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#181.
+
+struct ShExCompactPrinter;
+
+struct TripleExpr;
+
+impl ShExCompactPrinter {
+    fn pp_triple_expr(&self) -> impl Fn(&TripleExpr, &ShExCompactPrinter) + '_ {
+        move |te, printer| {
+            printer.pp_triple_expr()(te, printer);
+        }
+    }
+}
+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 785e5fdeb64..9b18a9715f2 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
@@ -4,12 +4,6 @@ error[E0282]: type annotations needed
 LL | fn muh(x: A) -> B {
    |        ^ cannot infer type
 
-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
+error: aborting due to 1 previous error
 
 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 99262f4bc4b..ec2963249f9 100644
--- a/tests/ui/impl-trait/two_tait_defining_each_other2.rs
+++ b/tests/ui/impl-trait/two_tait_defining_each_other2.rs
@@ -12,8 +12,7 @@ trait Foo {}
 fn muh(x: A) -> B {
     //[next]~^ ERROR: type annotations needed
     x // B's hidden type is A (opaquely)
-    //[next]~^ ERROR: type annotations needed
-    //[current]~^^ ERROR opaque type's hidden type cannot be another opaque type
+    //[current]~^ ERROR opaque type's hidden type cannot be another opaque type
 }
 
 struct Bar;
diff --git a/tests/ui/inference/return-block-type-inference-15965.stderr b/tests/ui/inference/return-block-type-inference-15965.stderr
index fc4f2defe7f..bfee9041922 100644
--- a/tests/ui/inference/return-block-type-inference-15965.stderr
+++ b/tests/ui/inference/return-block-type-inference-15965.stderr
@@ -1,10 +1,8 @@
 error[E0282]: type annotations needed
   --> $DIR/return-block-type-inference-15965.rs:5:9
    |
-LL | /         { return () }
-LL | |
-LL | |     ()
-   | |______^ cannot infer type
+LL |         { return () }
+   |         ^^^^^^^^^^^^^ cannot infer type
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-2.stderr b/tests/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-2.stderr
index 058dbb1e220..739182e120b 100644
--- a/tests/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-2.stderr
+++ b/tests/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-2.stderr
@@ -5,7 +5,7 @@ LL |     let mut closure0 = None;
    |         ^^^^^^^^^^^^
 ...
 LL |                         return c();
-   |                                --- type must be known at this point
+   |                                - type must be known at this point
    |
 help: consider giving `closure0` an explicit type, where the placeholders `_` are specified
    |