Make RPIT and TAIT work exactly the same

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -38,6 +38,15 @@ pub struct OpaqueTypeDecl<'tcx> {
     pub origin: hir::OpaqueTyOrigin,
 }
 
+pub enum ReplaceOpaqueTypes {
+    /// Closures can't create hidden types for opaque types of their parent, as they
+    /// do not have all the outlives information available. Also `type_of` looks for
+    /// hidden types in the owner (so the closure's parent), so it would not find these
+    /// definitions.
+    OnlyForRPIT,
+    All,
+}
+
 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn replace_opaque_types_with_inference_vars(
         &self,
@@ -46,27 +55,29 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         span: Span,
         code: ObligationCauseCode<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
+        replace: ReplaceOpaqueTypes,
     ) -> InferOk<'tcx, Ty<'tcx>> {
         if !ty.has_opaque_types() {
             return InferOk { value: ty, obligations: vec![] };
         }
         let mut obligations = vec![];
+        let replace_opaque_type = |def_id| match self.opaque_type_origin(def_id, span) {
+            None => false,
+            Some(OpaqueTyOrigin::FnReturn(..)) => true,
+            // Not using `==` or `matches!` here to make sure we exhaustively match variants.
+            Some(_) => match replace {
+                ReplaceOpaqueTypes::OnlyForRPIT => false,
+                ReplaceOpaqueTypes::All => true,
+            },
+        };
         let value = ty.fold_with(&mut ty::fold::BottomUpFolder {
             tcx: self.tcx,
             lt_op: |lt| lt,
             ct_op: |ct| ct,
             ty_op: |ty| match *ty.kind() {
-                // Closures can't create hidden types for opaque types of their parent, as they
+                ty::Opaque(def_id, _substs) if replace_opaque_type(def_id) => {
-                // do not have all the outlives information available. Also `type_of` looks for
+                    let def_span = self.tcx.def_span(def_id);
-                // hidden types in the owner (so the closure's parent), so it would not find these
+                    let span = if span.contains(def_span) { def_span } else { span };
-                // definitions.
-                ty::Opaque(def_id, _substs)
-                    if matches!(
-                        self.opaque_type_origin(def_id, span),
-                        Some(OpaqueTyOrigin::FnReturn(..))
-                    ) =>
-                {
-                    let span = if span.is_dummy() { self.tcx.def_span(def_id) } else { span };
                     let cause = ObligationCause::new(span, body_id, code.clone());
                     // FIXME(compiler-errors): We probably should add a new TypeVariableOriginKind
                     // for opaque types, and then use that kind to fix the spans for type errors

compiler/rustc_typeck/src/check/check.rs

@@ -13,6 +13,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ItemKind, Node, PathSegment};
+use rustc_infer::infer::opaque_types::ReplaceOpaqueTypes;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::Obligation;
@@ -95,9 +96,10 @@ pub(super) fn check_fn<'a, 'tcx>(
         fcx.register_infer_ok_obligations(fcx.infcx.replace_opaque_types_with_inference_vars(
             declared_ret_ty,
             body.value.hir_id,
-            DUMMY_SP,
+            decl.output.span(),
             traits::ObligationCauseCode::OpaqueReturnType(None),
             param_env,
+            ReplaceOpaqueTypes::All,
         ));
     // If we replaced declared_ret_ty with infer vars, then we must be infering
     // an opaque type, so set a flag so we can improve diagnostics.

compiler/rustc_typeck/src/check/closure.rs

@@ -7,6 +7,7 @@ use crate::rustc_middle::ty::subst::Subst;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
+use rustc_infer::infer::opaque_types::ReplaceOpaqueTypes;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_infer::infer::{InferOk, InferResult};
@@ -645,6 +646,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         result
     }
 
+    /// Closures can't create hidden types for opaque types of their parent, as they
+    /// do not have all the outlives information available. Also `type_of` looks for
+    /// hidden types in the owner (so the closure's parent), so it would not find these
+    /// definitions.
     fn hide_parent_opaque_types(&self, ty: Ty<'tcx>, span: Span, body_id: hir::HirId) -> Ty<'tcx> {
         let InferOk { value, obligations } = self.replace_opaque_types_with_inference_vars(
             ty,
@@ -652,6 +657,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             span,
             ObligationCauseCode::MiscObligation,
             self.param_env,
+            ReplaceOpaqueTypes::OnlyForRPIT,
         );
         self.register_predicates(obligations);
         value
@@ -671,38 +677,43 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let ret_ty = ret_coercion.borrow().expected_ty();
         let ret_ty = self.inh.infcx.shallow_resolve(ret_ty);
-        let (def_id, substs) = match *ret_ty.kind() {
-            ty::Opaque(def_id, substs) => (def_id, substs),
-            ty::Error(_) => return None,
-            _ => span_bug!(
-                self.tcx.def_span(expr_def_id),
-                "async fn generator return type not an inference variable"
-            ),
-        };
-
-        let item_bounds = self.tcx.bound_explicit_item_bounds(def_id);
 
+        let get_future_output = |predicate: ty::Predicate<'tcx>, span| {
             // Search for a pending obligation like
             //
             // `<R as Future>::Output = T`
             //
             // where R is the return type we are expecting. This type `T`
             // will be our output.
-        let output_ty = item_bounds
+            let bound_predicate = predicate.kind();
-            .transpose_iter()
+            if let ty::PredicateKind::Projection(proj_predicate) = bound_predicate.skip_binder() {
-            .map(|e| e.map_bound(|e| *e).transpose_tuple2())
-            .find_map(|(predicate, span)| {
-                let bound_predicate = predicate.subst(self.tcx, substs).kind();
-                if let ty::PredicateKind::Projection(proj_predicate) = bound_predicate.skip_binder()
-                {
                 self.deduce_future_output_from_projection(
-                        span.0,
+                    span,
                     bound_predicate.rebind(proj_predicate),
                 )
             } else {
                 None
             }
-            });
+        };
+
+        let output_ty = match *ret_ty.kind() {
+            ty::Infer(ty::TyVar(ret_vid)) => {
+                self.obligations_for_self_ty(ret_vid).find_map(|(_, obligation)| {
+                    get_future_output(obligation.predicate, obligation.cause.span)
+                })
+            }
+            ty::Opaque(def_id, substs) => self
+                .tcx
+                .bound_explicit_item_bounds(def_id)
+                .transpose_iter()
+                .map(|e| e.map_bound(|e| *e).transpose_tuple2())
+                .find_map(|(p, s)| get_future_output(p.subst(self.tcx, substs), s.0)),
+            ty::Error(_) => return None,
+            _ => span_bug!(
+                self.tcx.def_span(expr_def_id),
+                "async fn generator return type not an inference variable"
+            ),
+        };
 
         debug!("deduce_future_output_from_obligations: output_ty={:?}", output_ty);
         output_ty

src/test/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.rs

@@ -30,7 +30,7 @@ impl Thing for AssocNoCopy {
     type Out = Box<dyn Bar<Assoc: Copy>>;
 
     fn func() -> Self::Out {
-        Box::new(AssocNoCopy)
         //~^ ERROR the trait bound `String: Copy` is not satisfied
+        Box::new(AssocNoCopy)
     }
 }

src/test/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.stderr

@@ -1,10 +1,8 @@
 error[E0277]: the trait bound `String: Copy` is not satisfied
-  --> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:33:9
+  --> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:32:18
    |
-LL |         Box::new(AssocNoCopy)
+LL |     fn func() -> Self::Out {
-   |         ^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
+   |                  ^^^^^^^^^ the trait `Copy` is not implemented for `String`
-   |
-   = note: required for the cast from `AssocNoCopy` to the object type `dyn Bar<Assoc = <AssocNoCopy as Thing>::Out::{opaque#0}>`
 
 error: aborting due to previous error
 

src/test/ui/async-await/issues/issue-65159.rs

@@ -6,6 +6,7 @@ async fn copy() -> Result<()>
 //~^ ERROR this enum takes 2 generic arguments
 {
     Ok(())
+    //~^ ERROR type annotations needed
 }
 
 fn main() { }

src/test/ui/async-await/issues/issue-65159.stderr

@@ -16,6 +16,18 @@ help: add missing generic argument
 LL | async fn copy() -> Result<(), E>
    |                             +++
 
-error: aborting due to previous error
+error[E0282]: type annotations needed
+  --> $DIR/issue-65159.rs:8:5
+   |
+LL |     Ok(())
+   |     ^^ cannot infer type of the type parameter `E` declared on the enum `Result`
+   |
+help: consider specifying the generic arguments
+   |
+LL |     Ok::<(), E>(())
+   |       +++++++++
 
-For more information about this error, try `rustc --explain E0107`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0107, E0282.
+For more information about an error, try `rustc --explain E0107`.

src/test/ui/borrowck/issue-82126-mismatched-subst-and-hir.rs

@@ -17,6 +17,7 @@ async fn buy_lock(generator: &Mutex<MarketMultiplier>) -> LockedMarket<'_> {
     //~^ ERROR this struct takes 0 lifetime arguments but 1 lifetime argument was supplied
     //~^^ ERROR this struct takes 1 generic argument but 0 generic arguments were supplied
     LockedMarket(generator.lock().unwrap().buy())
+    //~^ ERROR cannot return value referencing temporary
 }
 
 struct LockedMarket<T>(T);

src/test/ui/borrowck/issue-82126-mismatched-subst-and-hir.stderr

@@ -7,7 +7,7 @@ LL | async fn buy_lock(generator: &Mutex<MarketMultiplier>) -> LockedMarket<'_>
    |                                                           expected 0 lifetime arguments
    |
 note: struct defined here, with 0 lifetime parameters
-  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:22:8
+  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:23:8
    |
 LL | struct LockedMarket<T>(T);
    |        ^^^^^^^^^^^^
@@ -19,7 +19,7 @@ LL | async fn buy_lock(generator: &Mutex<MarketMultiplier>) -> LockedMarket<'_>
    |                                                           ^^^^^^^^^^^^ expected 1 generic argument
    |
 note: struct defined here, with 1 generic parameter: `T`
-  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:22:8
+  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:23:8
    |
 LL | struct LockedMarket<T>(T);
    |        ^^^^^^^^^^^^ -
@@ -28,6 +28,16 @@ help: add missing generic argument
 LL | async fn buy_lock(generator: &Mutex<MarketMultiplier>) -> LockedMarket<'_, T> {
    |                                                                          +++
 
-error: aborting due to 2 previous errors
+error[E0515]: cannot return value referencing temporary value
+  --> $DIR/issue-82126-mismatched-subst-and-hir.rs:19:5
+   |
+LL |     LockedMarket(generator.lock().unwrap().buy())
+   |     ^^^^^^^^^^^^^-------------------------^^^^^^^
+   |     |            |
+   |     |            temporary value created here
+   |     returns a value referencing data owned by the current function
 
-For more information about this error, try `rustc --explain E0107`.
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0107, E0515.
+For more information about an error, try `rustc --explain E0107`.

src/test/ui/chalkify/bugs/async.stderr

@@ -29,13 +29,10 @@ LL |     T: Generator<ResumeTy, Yield = ()>,
    |                            ^^^^^^^^^^ required by this bound in `std::future::from_generator`
 
 error[E0280]: the requirement `<impl Future<Output = u32> as Future>::Output == u32` is not satisfied
-  --> $DIR/async.rs:7:29
+  --> $DIR/async.rs:7:25
    |
 LL | async fn foo(x: u32) -> u32 {
-   |  _____________________________^
+   |                         ^^^
-LL | |     x
-LL | | }
-   | |_^
 
 error: aborting due to 3 previous errors
 

src/test/ui/generic-associated-types/bugs/issue-89008.stderr

@@ -1,10 +1,10 @@
 error[E0271]: type mismatch resolving `<Empty<_> as Stream>::Item == Repr`
-  --> $DIR/issue-89008.rs:40:9
+  --> $DIR/issue-89008.rs:39:43
    |
 LL |     fn line_stream<'a, Repr>(&'a self) -> Self::LineStreamFut<'a, Repr> {
-   |                        ---- this type parameter
+   |                        ----               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type mismatch resolving `<Empty<_> as Stream>::Item == Repr`
-LL |         async {empty()}
+   |                        |
-   |         ^^^^^^^^^^^^^^^ type mismatch resolving `<Empty<_> as Stream>::Item == Repr`
+   |                        this type parameter
    |
 note: expected this to be `()`
   --> $DIR/issue-89008.rs:18:17

src/test/ui/impl-trait/issue-55872-1.rs

@@ -11,9 +11,9 @@ impl<S: Default> Bar for S {
 
     fn foo<T: Default>() -> Self::E {
         //~^ ERROR impl has stricter requirements than trait
-        (S::default(), T::default())
+        //~| ERROR the trait bound `S: Copy` is not satisfied in `(S, T)` [E0277]
-        //~^ ERROR the trait bound `S: Copy` is not satisfied in `(S, T)` [E0277]
         //~| ERROR the trait bound `T: Copy` is not satisfied in `(S, T)` [E0277]
+        (S::default(), T::default())
     }
 }
 

src/test/ui/impl-trait/issue-55872-1.stderr

@@ -8,10 +8,10 @@ LL |     fn foo<T: Default>() -> Self::E {
    |               ^^^^^^^ impl has extra requirement `T: Default`
 
 error[E0277]: the trait bound `S: Copy` is not satisfied in `(S, T)`
-  --> $DIR/issue-55872-1.rs:14:9
+  --> $DIR/issue-55872-1.rs:12:29
    |
-LL |         (S::default(), T::default())
+LL |     fn foo<T: Default>() -> Self::E {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `S`
+   |                             ^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `S`
    |
    = note: required because it appears within the type `(S, T)`
 help: consider further restricting this bound
@@ -20,10 +20,10 @@ LL | impl<S: Default + std::marker::Copy> Bar for S {
    |                 +++++++++++++++++++
 
 error[E0277]: the trait bound `T: Copy` is not satisfied in `(S, T)`
-  --> $DIR/issue-55872-1.rs:14:9
+  --> $DIR/issue-55872-1.rs:12:29
    |
-LL |         (S::default(), T::default())
+LL |     fn foo<T: Default>() -> Self::E {
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `T`
+   |                             ^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `T`
    |
    = note: required because it appears within the type `(S, T)`
 help: consider further restricting this bound

src/test/ui/impl-trait/issue-55872-3.rs

@@ -12,8 +12,8 @@ pub trait Bar {
 impl<S> Bar for S {
     type E = impl std::marker::Copy;
     fn foo<T>() -> Self::E {
-        async {}
     //~^ ERROR the trait bound `impl Future<Output = ()>: Copy` is not satisfied [E0277]
+        async {}
     }
 }
 

src/test/ui/impl-trait/issue-55872-3.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `impl Future<Output = ()>: Copy` is not satisfied
-  --> $DIR/issue-55872-3.rs:15:9
+  --> $DIR/issue-55872-3.rs:14:20
    |
-LL |         async {}
+LL |     fn foo<T>() -> Self::E {
-   |         ^^^^^^^^ the trait `Copy` is not implemented for `impl Future<Output = ()>`
+   |                    ^^^^^^^ the trait `Copy` is not implemented for `impl Future<Output = ()>`
 
 error: aborting due to previous error
 

src/test/ui/impl-trait/issues/issue-70877.rs

@@ -13,7 +13,7 @@ impl Iterator for Bar {
     type Item = FooItem;
 
     fn next(&mut self) -> Option<Self::Item> {
-        Some(Box::new(quux)) //~ ERROR mismatched types
+        Some(Box::new(quux))
     }
 }
 

src/test/ui/impl-trait/issues/issue-70877.stderr

@@ -1,17 +1,3 @@
-error[E0308]: mismatched types
-  --> $DIR/issue-70877.rs:16:9
-   |
-LL | type FooRet = impl std::fmt::Debug;
-   |               -------------------- the expected opaque type
-...
-LL |     fn next(&mut self) -> Option<Self::Item> {
-   |                           ------------------ expected `Option<Box<(dyn for<'r> Fn(&'r (dyn ToString + 'r)) -> FooRet + 'static)>>` because of return type
-LL |         Some(Box::new(quux))
-   |         ^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn Fn`, found fn item
-   |
-   = note: expected enum `Option<Box<(dyn for<'r> Fn(&'r (dyn ToString + 'r)) -> FooRet + 'static)>>`
-              found enum `Option<Box<for<'r> fn(&'r (dyn ToString + 'r)) -> FooRet {quux}>>`
-
 error: opaque type's hidden type cannot be another opaque type from the same scope
   --> $DIR/issue-70877.rs:31:12
    |
@@ -29,6 +15,5 @@ note: opaque type being used as hidden type
 LL | type FooRet = impl std::fmt::Debug;
    |               ^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.

src/test/ui/impl-trait/issues/issue-78722.rs

@@ -7,7 +7,8 @@ type F = impl core::future::Future<Output = u8>;
 struct Bug {
     V1: [(); {
         fn concrete_use() -> F {
-            async {} //~ ERROR type mismatch
+            //~^ ERROR type mismatch
+            async {}
         }
         let f: F = async { 1 };
         //~^ ERROR `async` blocks are not allowed in constants

src/test/ui/impl-trait/issues/issue-78722.stderr

@@ -1,5 +1,5 @@
 error[E0658]: `async` blocks are not allowed in constants
-  --> $DIR/issue-78722.rs:12:20
+  --> $DIR/issue-78722.rs:13:20
    |
 LL |         let f: F = async { 1 };
    |                    ^^^^^^^^^^^
@@ -8,7 +8,7 @@ LL |         let f: F = async { 1 };
    = help: add `#![feature(const_async_blocks)]` to the crate attributes to enable
 
 error[E0493]: destructors cannot be evaluated at compile-time
-  --> $DIR/issue-78722.rs:12:13
+  --> $DIR/issue-78722.rs:13:13
    |
 LL |         let f: F = async { 1 };
    |             ^ constants cannot evaluate destructors
@@ -17,10 +17,10 @@ LL |     }],
    |     - value is dropped here
 
 error[E0271]: type mismatch resolving `<impl Future<Output = ()> as Future>::Output == u8`
-  --> $DIR/issue-78722.rs:10:13
+  --> $DIR/issue-78722.rs:9:30
    |
-LL |             async {}
+LL |         fn concrete_use() -> F {
-   |             ^^^^^^^^ expected `()`, found `u8`
+   |                              ^ expected `()`, found `u8`
 
 error: aborting due to 3 previous errors
 

src/test/ui/impl-trait/issues/issue-83919.rs

@@ -19,8 +19,9 @@ impl Foo for Implementor {
     type Fut = impl Future<Output=Self::Fut2>;
 
     fn get_fut(&self) -> Self::Fut {
+    //~^ ERROR `{integer}` is not a future
         async move {
-            42 //~^ ERROR `{integer}` is not a future
+            42
             // 42 does not impl Future and rustc does actually point out the error,
             // but rustc used to panic.
             // Putting a valid Future here always worked fine.

src/test/ui/impl-trait/issues/issue-83919.stderr

@@ -1,13 +1,8 @@
 error[E0277]: `{integer}` is not a future
-  --> $DIR/issue-83919.rs:22:9
+  --> $DIR/issue-83919.rs:21:26
    |
-LL | /         async move {
+LL |     fn get_fut(&self) -> Self::Fut {
-LL | |             42
+   |                          ^^^^^^^^^ `{integer}` is not a future
-LL | |             // 42 does not impl Future and rustc does actually point out the error,
-LL | |             // but rustc used to panic.
-LL | |             // Putting a valid Future here always worked fine.
-LL | |         }
-   | |_________^ `{integer}` is not a future
    |
    = help: the trait `Future` is not implemented for `{integer}`
    = note: {integer} must be a future or must implement `IntoFuture` to be awaited

src/test/ui/impl-trait/nested-return-type2-tait2.rs

@@ -24,8 +24,8 @@ type Traitable = impl Trait<Assoc = Sendable>;
 // var to make it uphold the `: Duh` bound on `Trait::Assoc`. The opaque
 // type does not implement `Duh`, even if its hidden type does. So we error out.
 fn foo() -> Traitable {
-    || 42
     //~^ ERROR `Sendable: Duh` is not satisfied
+    || 42
 }
 
 fn main() {

src/test/ui/impl-trait/nested-return-type2-tait2.stderr

@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `Sendable: Duh` is not satisfied
-  --> $DIR/nested-return-type2-tait2.rs:27:5
+  --> $DIR/nested-return-type2-tait2.rs:26:13
    |
-LL |     || 42
+LL | fn foo() -> Traitable {
-   |     ^^^^^ the trait `Duh` is not implemented for `Sendable`
+   |             ^^^^^^^^^ the trait `Duh` is not implemented for `Sendable`
    |
    = help: the trait `Duh` is implemented for `i32`
-note: required because of the requirements on the impl of `Trait` for `[closure@$DIR/nested-return-type2-tait2.rs:27:5: 27:10]`
+note: required because of the requirements on the impl of `Trait` for `[closure@$DIR/nested-return-type2-tait2.rs:28:5: 28:10]`
   --> $DIR/nested-return-type2-tait2.rs:14:31
    |
 LL | impl<R: Duh, F: FnMut() -> R> Trait for F {

src/test/ui/impl-trait/nested-return-type2-tait3.rs

@@ -23,8 +23,8 @@ type Traitable = impl Trait<Assoc = impl Send>;
 // var to make it uphold the `: Duh` bound on `Trait::Assoc`. The opaque
 // type does not implement `Duh`, even if its hidden type does. So we error out.
 fn foo() -> Traitable {
-    || 42
     //~^ ERROR `impl Send: Duh` is not satisfied
+    || 42
 }
 
 fn main() {

src/test/ui/impl-trait/nested-return-type2-tait3.stderr

@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `impl Send: Duh` is not satisfied
-  --> $DIR/nested-return-type2-tait3.rs:26:5
+  --> $DIR/nested-return-type2-tait3.rs:25:13
    |
-LL |     || 42
+LL | fn foo() -> Traitable {
-   |     ^^^^^ the trait `Duh` is not implemented for `impl Send`
+   |             ^^^^^^^^^ the trait `Duh` is not implemented for `impl Send`
    |
    = help: the trait `Duh` is implemented for `i32`
-note: required because of the requirements on the impl of `Trait` for `[closure@$DIR/nested-return-type2-tait3.rs:26:5: 26:10]`
+note: required because of the requirements on the impl of `Trait` for `[closure@$DIR/nested-return-type2-tait3.rs:27:5: 27:10]`
   --> $DIR/nested-return-type2-tait3.rs:14:31
    |
 LL | impl<R: Duh, F: FnMut() -> R> Trait for F {

src/test/ui/lazy-type-alias-impl-trait/branches.rs

@@ -1,5 +1,7 @@
 #![feature(type_alias_impl_trait)]
 
+// check-pass
+
 type Foo = impl std::fmt::Debug;
 
 fn foo(b: bool) -> Foo {
@@ -7,7 +9,6 @@ fn foo(b: bool) -> Foo {
         vec![42_i32]
     } else {
         std::iter::empty().collect()
-        //~^ ERROR `Foo` cannot be built from an iterator over elements of type `_`
     }
 }
 

src/test/ui/lazy-type-alias-impl-trait/branches.stderr

@@ -1,16 +0,0 @@
-error[E0277]: a value of type `Foo` cannot be built from an iterator over elements of type `_`
-  --> $DIR/branches.rs:9:28
-   |
-LL |         std::iter::empty().collect()
-   |                            ^^^^^^^ value of type `Foo` cannot be built from `std::iter::Iterator<Item=_>`
-   |
-   = help: the trait `FromIterator<_>` is not implemented for `Foo`
-note: required by a bound in `collect`
-  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
-   |
-LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `collect`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0277`.

src/test/ui/lazy-type-alias-impl-trait/branches2.rs

@@ -1,6 +1,6 @@
 #![feature(type_alias_impl_trait)]
 
-// run-pass
+// check-pass
 
 type Foo = impl std::iter::FromIterator<i32> + PartialEq<Vec<i32>> + std::fmt::Debug;
 

src/test/ui/lazy-type-alias-impl-trait/branches3.rs

@@ -0,0 +1,36 @@
+#![feature(type_alias_impl_trait)]
+
+type Foo = impl for<'a> FnOnce(&'a str) -> usize;
+type Bar = impl FnOnce(&'static str) -> usize;
+
+fn foo() -> Foo {
+    if true {
+        |s| s.len() //~ ERROR type annotations needed
+    } else {
+        panic!()
+    }
+}
+fn bar() -> Bar {
+    if true {
+        |s| s.len() //~ ERROR type annotations needed
+    } else {
+        panic!()
+    }
+}
+
+fn foo2() -> impl for<'a> FnOnce(&'a str) -> usize {
+    if true {
+        |s| s.len() //~ ERROR type annotations needed
+    } else {
+        panic!()
+    }
+}
+fn bar2() -> impl FnOnce(&'static str) -> usize {
+    if true {
+        |s| s.len() //~ ERROR type annotations needed
+    } else {
+        panic!()
+    }
+}
+
+fn main() {}

src/test/ui/lazy-type-alias-impl-trait/branches3.stderr

@@ -0,0 +1,51 @@
+error[E0282]: type annotations needed
+  --> $DIR/branches3.rs:8:10
+   |
+LL |         |s| s.len()
+   |          ^
+   |
+   = note: type must be known at this point
+help: consider giving this closure parameter an explicit type
+   |
+LL |         |s: _| s.len()
+   |           +++
+
+error[E0282]: type annotations needed
+  --> $DIR/branches3.rs:15:10
+   |
+LL |         |s| s.len()
+   |          ^
+   |
+   = note: type must be known at this point
+help: consider giving this closure parameter an explicit type
+   |
+LL |         |s: _| s.len()
+   |           +++
+
+error[E0282]: type annotations needed
+  --> $DIR/branches3.rs:23:10
+   |
+LL |         |s| s.len()
+   |          ^
+   |
+   = note: type must be known at this point
+help: consider giving this closure parameter an explicit type
+   |
+LL |         |s: _| s.len()
+   |           +++
+
+error[E0282]: type annotations needed
+  --> $DIR/branches3.rs:30:10
+   |
+LL |         |s| s.len()
+   |          ^
+   |
+   = note: type must be known at this point
+help: consider giving this closure parameter an explicit type
+   |
+LL |         |s: _| s.len()
+   |           +++
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/lazy-type-alias-impl-trait/recursion2.rs

@@ -1,5 +1,7 @@
 #![feature(type_alias_impl_trait)]
 
+// check-pass
+
 type Foo = impl std::fmt::Debug;
 
 fn foo(b: bool) -> Foo {
@@ -7,7 +9,7 @@ fn foo(b: bool) -> Foo {
         return vec![];
     }
     let x: Vec<i32> = foo(false);
-    std::iter::empty().collect() //~ ERROR `Foo` cannot be built from an iterator
+    std::iter::empty().collect()
 }
 
 fn bar(b: bool) -> impl std::fmt::Debug {

src/test/ui/lazy-type-alias-impl-trait/recursion2.stderr

@@ -1,16 +0,0 @@
-error[E0277]: a value of type `Foo` cannot be built from an iterator over elements of type `_`
-  --> $DIR/recursion2.rs:10:24
-   |
-LL |     std::iter::empty().collect()
-   |                        ^^^^^^^ value of type `Foo` cannot be built from `std::iter::Iterator<Item=_>`
-   |
-   = help: the trait `FromIterator<_>` is not implemented for `Foo`
-note: required by a bound in `collect`
-  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
-   |
-LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `collect`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0277`.

src/test/ui/never_type/impl_trait_fallback2.rs

@@ -13,6 +13,7 @@ fn should_ret_unit() -> impl T {
 type Foo = impl T;
 
 fn a() -> Foo {
+    //~^ ERROR `(): T` is not satisfied
     panic!()
 }
 

src/test/ui/never_type/impl_trait_fallback2.stderr

@@ -6,6 +6,14 @@ LL | fn should_ret_unit() -> impl T {
    |
    = help: the trait `T` is implemented for `i32`
 
-error: aborting due to previous error
+error[E0277]: the trait bound `(): T` is not satisfied
+  --> $DIR/impl_trait_fallback2.rs:15:11
+   |
+LL | fn a() -> Foo {
+   |           ^^^ the trait `T` is not implemented for `()`
+   |
+   = help: the trait `T` is implemented for `i32`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/never_type/impl_trait_fallback3.rs

@@ -7,9 +7,9 @@ trait T {
 }
 
 type Foo = impl T;
-//~^ ERROR unconstrained opaque type
 
 fn a() -> Foo {
+    //~^ ERROR the trait bound `(): T` is not satisfied
     // This is not a defining use, it doesn't actually constrain the opaque type.
     panic!()
 }

src/test/ui/never_type/impl_trait_fallback3.stderr

@@ -1,10 +1,9 @@
-error: unconstrained opaque type
+error[E0277]: the trait bound `(): T` is not satisfied
-  --> $DIR/impl_trait_fallback3.rs:9:12
+  --> $DIR/impl_trait_fallback3.rs:11:11
    |
-LL | type Foo = impl T;
+LL | fn a() -> Foo {
-   |            ^^^^^^
+   |           ^^^ the trait `T` is not implemented for `()`
-   |
-   = note: `Foo` must be used in combination with a concrete type within the same module
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/closures_in_branches.rs

@@ -4,7 +4,7 @@ type Foo = impl std::ops::FnOnce(String) -> usize;
 
 fn foo(b: bool) -> Foo {
     if b {
-        |x| x.len()
+        |x| x.len() //~ ERROR type annotations needed
     } else {
         panic!()
     }

src/test/ui/type-alias-impl-trait/closures_in_branches.stderr

@@ -1,3 +1,15 @@
+error[E0282]: type annotations needed
+  --> $DIR/closures_in_branches.rs:7:10
+   |
+LL |         |x| x.len()
+   |          ^
+   |
+   = note: type must be known at this point
+help: consider giving this closure parameter an explicit type
+   |
+LL |         |x: _| x.len()
+   |           +++
+
 error[E0282]: type annotations needed
   --> $DIR/closures_in_branches.rs:21:10
    |
@@ -10,6 +22,6 @@ help: consider giving this closure parameter an explicit type
 LL |         |x: _| x.len()
    |           +++
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0282`.

src/test/ui/type-alias-impl-trait/fallback.rs

@@ -1,7 +1,6 @@
 // Tests that we correctly handle opaque types being used opaquely,
 // even within their defining scope.
 //
-// check-pass
 #![feature(type_alias_impl_trait)]
 
 type Foo = impl Copy;
@@ -23,6 +22,7 @@ fn constrained_foo() -> Foo {
 // constraints on it.
 fn unconstrained_foo() -> Wrapper<Foo> {
     Wrapper::Second
+    //~^ ERROR: type annotations needed
 }
 
 fn main() {}

src/test/ui/type-alias-impl-trait/fallback.stderr

@@ -0,0 +1,15 @@
+error[E0283]: type annotations needed
+  --> $DIR/fallback.rs:24:5
+   |
+LL |     Wrapper::Second
+   |     ^^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the enum `Wrapper`
+   |
+   = note: cannot satisfy `_: Copy`
+help: consider specifying the generic argument
+   |
+LL |     Wrapper::<T>::Second
+   |            +++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0283`.

src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.rs

@@ -3,7 +3,8 @@
 type Foo = impl Fn() -> Foo;
 
 fn foo() -> Foo {
-    foo //~ ERROR: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
+//~^ ERROR: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
+    foo
 }
 
 fn main() {}

src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr

@@ -1,7 +1,7 @@
 error[E0275]: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
-  --> $DIR/issue-53398-cyclic-types.rs:6:5
+  --> $DIR/issue-53398-cyclic-types.rs:5:13
    |
-LL |     foo
+LL | fn foo() -> Foo {
    |             ^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_53398_cyclic_types`)

src/test/ui/type-alias-impl-trait/issue-60371.stderr

@@ -11,7 +11,7 @@ error[E0277]: the trait bound `(): Bug` is not satisfied
   --> $DIR/issue-60371.rs:10:40
    |
 LL |     const FUN: fn() -> Self::Item = || ();
-   |                                        ^^ the trait `Bug` is not implemented for `()`
+   |                                        ^ the trait `Bug` is not implemented for `()`
    |
    = help: the trait `Bug` is implemented for `&()`
 

src/test/ui/type-alias-impl-trait/issue-63279.rs

@@ -5,6 +5,7 @@
 type Closure = impl FnOnce();
 
 fn c() -> Closure {
+    //~^ ERROR: expected a `FnOnce<()>` closure, found `()`
     || -> Closure { || () }
     //~^ ERROR: mismatched types
     //~| ERROR: mismatched types

src/test/ui/type-alias-impl-trait/issue-63279.stderr

@@ -1,5 +1,14 @@
 error[E0277]: expected a `FnOnce<()>` closure, found `()`
-  --> $DIR/issue-63279.rs:8:11
+  --> $DIR/issue-63279.rs:7:11
+   |
+LL | fn c() -> Closure {
+   |           ^^^^^^^ expected an `FnOnce<()>` closure, found `()`
+   |
+   = help: the trait `FnOnce<()>` is not implemented for `()`
+   = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
+
+error[E0277]: expected a `FnOnce<()>` closure, found `()`
+  --> $DIR/issue-63279.rs:9:11
    |
 LL |     || -> Closure { || () }
    |           ^^^^^^^ expected an `FnOnce<()>` closure, found `()`
@@ -8,33 +17,32 @@ LL |     || -> Closure { || () }
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
 
 error[E0308]: mismatched types
-  --> $DIR/issue-63279.rs:8:21
+  --> $DIR/issue-63279.rs:9:21
    |
 LL |     || -> Closure { || () }
    |                     ^^^^^ expected `()`, found closure
    |
    = note: expected unit type `()`
-                found closure `[closure@$DIR/issue-63279.rs:8:21: 8:26]`
+                found closure `[closure@$DIR/issue-63279.rs:9:21: 9:26]`
 help: use parentheses to call this closure
    |
 LL |     || -> Closure { (|| ())() }
    |                     +     +++
 
 error[E0308]: mismatched types
-  --> $DIR/issue-63279.rs:8:5
+  --> $DIR/issue-63279.rs:9:5
    |
-LL | type Closure = impl FnOnce();
-   |                ------------- the expected opaque type
-LL |
-LL | fn c() -> Closure {
-   |           ------- expected `Closure` because of return type
 LL |     || -> Closure { || () }
    |     ^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found closure
    |
-   = note: expected opaque type `Closure`
+   = note: expected unit type `()`
-                  found closure `[closure@$DIR/issue-63279.rs:8:5: 8:28]`
+                found closure `[closure@$DIR/issue-63279.rs:9:5: 9:28]`
+help: use parentheses to call this closure
+   |
+LL |     (|| -> Closure { || () })()
+   |     +                       +++
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0277, E0308.
 For more information about an error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/issue-74280.stderr

@@ -1,17 +1,11 @@
 error[E0308]: mismatched types
   --> $DIR/issue-74280.rs:9:5
    |
-LL | type Test = impl Copy;
-   |             --------- the expected opaque type
-LL |
 LL | fn test() -> Test {
-   |              ---- expected `Test` because of return type
+   |              ---- expected `_` because of return type
 LL |     let y = || -> Test { () };
 LL |     7
    |     ^ expected `()`, found integer
-   |
-   = note: expected opaque type `Test`
-                     found type `{integer}`
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/issue-94429.rs

@@ -13,7 +13,8 @@ impl Runnable for Implementor {
     type Gen = impl Generator<Yield = (), Return = ()>;
 
     fn run(&mut self) -> Self::Gen {
-        move || { //~ ERROR: type mismatch resolving
+    //~^ ERROR: type mismatch resolving
+        move || {
             yield 1;
         }
     }

src/test/ui/type-alias-impl-trait/issue-94429.stderr

@@ -1,10 +1,8 @@
-error[E0271]: type mismatch resolving `<[generator@$DIR/issue-94429.rs:16:9: 18:10] as Generator>::Yield == ()`
+error[E0271]: type mismatch resolving `<[generator@$DIR/issue-94429.rs:17:9: 19:10] as Generator>::Yield == ()`
-  --> $DIR/issue-94429.rs:16:9
+  --> $DIR/issue-94429.rs:15:26
    |
-LL | /         move || {
+LL |     fn run(&mut self) -> Self::Gen {
-LL | |             yield 1;
+   |                          ^^^^^^^^^ expected integer, found `()`
-LL | |         }
-   | |_________^ expected integer, found `()`
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn.rs

@@ -7,8 +7,8 @@
 type X<A, B> = impl Into<&'static A>;
 
 fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
-    (a, a)
     //~^ ERROR the trait bound `&'static B: From<&A>` is not satisfied
+    (a, a)
 }
 
 fn main() {

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `&'static B: From<&A>` is not satisfied
-  --> $DIR/multiple-def-uses-in-one-fn.rs:10:9
+  --> $DIR/multiple-def-uses-in-one-fn.rs:9:45
    |
-LL |     (a, a)
+LL | fn f<A, B: 'static>(a: &'static A, b: B) -> (X<A, B>, X<B, A>) {
-   |         ^ the trait `From<&A>` is not implemented for `&'static B`
+   |                                             ^^^^^^^^^^^^^^^^^^ the trait `From<&A>` is not implemented for `&'static B`
    |
    = note: required because of the requirements on the impl of `Into<&'static B>` for `&A`
 help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn3.stderr

@@ -1,9 +1,6 @@
 error[E0308]: mismatched types
   --> $DIR/multiple-def-uses-in-one-fn3.rs:14:9
    |
-LL | type X<A: ToString + Clone, B: ToString + Clone> = impl ToString;
-   |                                                    ------------- the expected opaque type
-...
 LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>) {
    |      -                    - found type parameter
    |      |
@@ -11,7 +8,7 @@ LL | fn g<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A
 LL |     (a, b)
    |         ^ expected type parameter `A`, found type parameter `B`
    |
-   = note: expected opaque type `X<A, B>`
+   = note: expected type parameter `A`
               found type parameter `B`
    = note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
    = note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters

src/test/ui/type-alias-impl-trait/self-referential-2.rs

@@ -4,7 +4,7 @@ type Foo = impl std::fmt::Debug;
 type Bar = impl PartialEq<Foo>;
 
 fn bar() -> Bar {
-    42_i32 //~ ERROR can't compare `i32` with `Foo`
+    42_i32 //~^ ERROR can't compare `i32` with `Foo`
 }
 
 fn main() {}

src/test/ui/type-alias-impl-trait/self-referential-2.stderr

@@ -1,8 +1,10 @@
 error[E0277]: can't compare `i32` with `Foo`
-  --> $DIR/self-referential-2.rs:7:5
+  --> $DIR/self-referential-2.rs:6:13
    |
+LL | fn bar() -> Bar {
+   |             ^^^ no implementation for `i32 == Foo`
 LL |     42_i32
-   |     ^^^^^^ no implementation for `i32 == Foo`
+   |     ------ return type was inferred to be `i32` here
    |
    = help: the trait `PartialEq<Foo>` is not implemented for `i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:

src/test/ui/type-alias-impl-trait/self-referential-4.rs

@@ -3,19 +3,19 @@
 type Bar<'a, 'b> = impl PartialEq<Bar<'b, 'static>> + std::fmt::Debug;
 
 fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
-    i //~ ERROR can't compare `&i32` with `Bar<'b, 'static>`
+    i //~^ ERROR can't compare `&i32` with `Bar<'b, 'static>`
 }
 
 type Foo<'a, 'b> = impl PartialEq<Foo<'static, 'b>> + std::fmt::Debug;
 
 fn foo<'a, 'b>(i: &'a i32) -> Foo<'a, 'b> {
-    i //~ ERROR can't compare `&i32` with `Foo<'static, 'b>`
+    i //~^ ERROR can't compare `&i32` with `Foo<'static, 'b>`
 }
 
 type Moo<'a, 'b> = impl PartialEq<Moo<'static, 'a>> + std::fmt::Debug;
 
 fn moo<'a, 'b>(i: &'a i32) -> Moo<'a, 'b> {
-    i //~ ERROR can't compare `&i32` with `Moo<'static, 'a>`
+    i //~^ ERROR can't compare `&i32` with `Moo<'static, 'a>`
 }
 
 fn main() {

src/test/ui/type-alias-impl-trait/self-referential-4.stderr

@@ -1,8 +1,10 @@
 error[E0277]: can't compare `&i32` with `Bar<'b, 'static>`
-  --> $DIR/self-referential-4.rs:6:5
+  --> $DIR/self-referential-4.rs:5:31
    |
+LL | fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == Bar<'b, 'static>`
 LL |     i
-   |     ^ no implementation for `&i32 == Bar<'b, 'static>`
+   |     - return type was inferred to be `&i32` here
    |
    = help: the trait `PartialEq<Bar<'b, 'static>>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:
@@ -17,10 +19,12 @@ LL |     i
            and 6 others
 
 error[E0277]: can't compare `&i32` with `Foo<'static, 'b>`
-  --> $DIR/self-referential-4.rs:12:5
+  --> $DIR/self-referential-4.rs:11:31
    |
+LL | fn foo<'a, 'b>(i: &'a i32) -> Foo<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == Foo<'static, 'b>`
 LL |     i
-   |     ^ no implementation for `&i32 == Foo<'static, 'b>`
+   |     - return type was inferred to be `&i32` here
    |
    = help: the trait `PartialEq<Foo<'static, 'b>>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:
@@ -35,10 +39,12 @@ LL |     i
            and 6 others
 
 error[E0277]: can't compare `&i32` with `Moo<'static, 'a>`
-  --> $DIR/self-referential-4.rs:18:5
+  --> $DIR/self-referential-4.rs:17:31
    |
+LL | fn moo<'a, 'b>(i: &'a i32) -> Moo<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == Moo<'static, 'a>`
 LL |     i
-   |     ^ no implementation for `&i32 == Moo<'static, 'a>`
+   |     - return type was inferred to be `&i32` here
    |
    = help: the trait `PartialEq<Moo<'static, 'a>>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:

src/test/ui/type-alias-impl-trait/self-referential.rs

@@ -3,19 +3,22 @@
 type Bar<'a, 'b> = impl PartialEq<Bar<'b, 'a>> + std::fmt::Debug;
 
 fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
-    i //~ ERROR can't compare `&i32` with `Bar<'b, 'a>`
+    //~^ ERROR can't compare `&i32` with `Bar<'b, 'a>`
+    i
 }
 
 type Foo<'a, 'b> = (i32, impl PartialEq<Foo<'a, 'b>> + std::fmt::Debug);
 
 fn foo<'a, 'b>(i: &'a i32) -> Foo<'a, 'b> {
-    (42, i) //~ ERROR can't compare `&i32` with `(i32, &i32)`
+    //~^ ERROR can't compare `&i32` with `(i32, &i32)`
+    (42, i)
 }
 
 type Moo<'a, 'b> = (i32, impl PartialEq<Moo<'b, 'a>> + std::fmt::Debug);
 
 fn moo<'a, 'b>(i: &'a i32) -> Moo<'a, 'b> {
-    (42, i) //~ ERROR can't compare `&i32` with `(i32, Moo<'b, 'a>::{opaque#0})`
+    //~^ ERROR can't compare `&i32` with `(i32, Moo<'b, 'a>::{opaque#0})`
+    (42, i)
 }
 
 fn main() {

src/test/ui/type-alias-impl-trait/self-referential.stderr

@@ -1,8 +1,11 @@
 error[E0277]: can't compare `&i32` with `Bar<'b, 'a>`
-  --> $DIR/self-referential.rs:6:5
+  --> $DIR/self-referential.rs:5:31
    |
+LL | fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == Bar<'b, 'a>`
+LL |
 LL |     i
-   |     ^ no implementation for `&i32 == Bar<'b, 'a>`
+   |     - return type was inferred to be `&i32` here
    |
    = help: the trait `PartialEq<Bar<'b, 'a>>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:
@@ -17,10 +20,13 @@ LL |     i
            and 6 others
 
 error[E0277]: can't compare `&i32` with `(i32, &i32)`
-  --> $DIR/self-referential.rs:12:10
+  --> $DIR/self-referential.rs:12:31
    |
+LL | fn foo<'a, 'b>(i: &'a i32) -> Foo<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == (i32, &i32)`
+LL |
 LL |     (42, i)
-   |          ^ no implementation for `&i32 == (i32, &i32)`
+   |     ------- return type was inferred to be `(i32, &i32)` here
    |
    = help: the trait `PartialEq<(i32, &i32)>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`:
@@ -35,10 +41,13 @@ LL |     (42, i)
            and 6 others
 
 error[E0277]: can't compare `&i32` with `(i32, Moo<'b, 'a>::{opaque#0})`
-  --> $DIR/self-referential.rs:18:10
+  --> $DIR/self-referential.rs:19:31
    |
+LL | fn moo<'a, 'b>(i: &'a i32) -> Moo<'a, 'b> {
+   |                               ^^^^^^^^^^^ no implementation for `&i32 == (i32, Moo<'b, 'a>::{opaque#0})`
+LL |
 LL |     (42, i)
-   |          ^ no implementation for `&i32 == (i32, Moo<'b, 'a>::{opaque#0})`
+   |     ------- return type was inferred to be `(i32, &i32)` here
    |
    = help: the trait `PartialEq<(i32, Moo<'b, 'a>::{opaque#0})>` is not implemented for `&i32`
    = help: the following other types implement trait `PartialEq<Rhs>`: