Rollup merge of #99383 - ouz-a:issue_57961, r=oli-obk

Formalize defining_use_anchor

This tackles issue #57961

Introduces new enum called `DefiningAnchor` that replaces `Option<LocalDefId>` of `defining_use_anchor`. Now every use of it is explicit and exhaustively matched, catching errors like one in the linked issue. This is not a perfect fix but it's a step in the right direction.

r? `@oli-obk`

10 files changed, 108 insertions, 35 deletions

diff --git a/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs b/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs
index d29a82f76a7..b05579f2166 100644
--- a/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs
+++ b/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.rs
@@ -6,7 +6,7 @@ type Tait = impl Sized;
 
 impl Foo for Concrete {
     type Item = Concrete;
-    //~^ mismatched types
+    //~^ type mismatch resolving
 }
 
 impl Bar for Concrete {
diff --git a/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.stderr b/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.stderr
index a25f0cd8761..f0dceb1b11a 100644
--- a/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.stderr
+++ b/src/test/ui/impl-trait/issues/issue-99348-impl-compatibility.stderr
@@ -1,15 +1,25 @@
-error[E0308]: mismatched types
+error[E0271]: type mismatch resolving `<Concrete as Bar>::Other == Concrete`
   --> $DIR/issue-99348-impl-compatibility.rs:8:17
    |
 LL | type Tait = impl Sized;
-   |             ---------- the expected opaque type
+   |             ---------- the found opaque type
 ...
 LL |     type Item = Concrete;
-   |                 ^^^^^^^^ types differ
+   |                 ^^^^^^^^ type mismatch resolving `<Concrete as Bar>::Other == Concrete`
    |
-   = note: expected opaque type `Tait`
-                   found struct `Concrete`
+note: expected this to be `Concrete`
+  --> $DIR/issue-99348-impl-compatibility.rs:13:18
+   |
+LL |     type Other = Tait;
+   |                  ^^^^
+   = note:   expected struct `Concrete`
+           found opaque type `Tait`
+note: required by a bound in `Foo::Item`
+  --> $DIR/issue-99348-impl-compatibility.rs:17:20
+   |
+LL |     type Item: Bar<Other = Self>;
+   |                    ^^^^^^^^^^^^ required by this bound in `Foo::Item`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0271`.
diff --git a/src/test/ui/parser/fn-header-semantic-fail.rs b/src/test/ui/parser/fn-header-semantic-fail.rs
index c2954868f78..8ff14fb1f30 100644
--- a/src/test/ui/parser/fn-header-semantic-fail.rs
+++ b/src/test/ui/parser/fn-header-semantic-fail.rs
@@ -27,7 +27,7 @@ fn main() {
     struct Y;
     impl X for Y {
         async fn ft1() {} //~ ERROR functions in traits cannot be declared `async`
-        //~^ ERROR impl has stricter requirements than trait
+        //~^ ERROR has an incompatible type for trait
         unsafe fn ft2() {} // OK.
         const fn ft3() {} //~ ERROR functions in traits cannot be declared const
         extern "C" fn ft4() {}
@@ -36,7 +36,7 @@ fn main() {
         //~| ERROR functions in traits cannot be declared const
         //~| ERROR functions cannot be both `const` and `async`
         //~| ERROR cycle detected
-        //~| ERROR impl has stricter requirements than trait
+        //~| ERROR has an incompatible type for trait
     }
 
     impl Y {
diff --git a/src/test/ui/parser/fn-header-semantic-fail.stderr b/src/test/ui/parser/fn-header-semantic-fail.stderr
index 75d27c614e2..bc51ba8b8c5 100644
--- a/src/test/ui/parser/fn-header-semantic-fail.stderr
+++ b/src/test/ui/parser/fn-header-semantic-fail.stderr
@@ -216,23 +216,41 @@ LL | |     }
 LL | | }
    | |_^
 
-error[E0276]: impl has stricter requirements than trait
-  --> $DIR/fn-header-semantic-fail.rs:29:9
+error[E0053]: method `ft1` has an incompatible type for trait
+  --> $DIR/fn-header-semantic-fail.rs:29:24
    |
-LL |         async fn ft1();
-   |         --------------- definition of `ft1` from trait
-...
 LL |         async fn ft1() {}
-   |         ^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
+   |                        ^
+   |                        |
+   |                        checked the `Output` of this `async fn`, found opaque type
+   |                        expected `()`, found opaque type
+   |
+   = note: while checking the return type of the `async fn`
+note: type in trait
+  --> $DIR/fn-header-semantic-fail.rs:17:23
+   |
+LL |         async fn ft1();
+   |                       ^
+   = note: expected fn pointer `fn()`
+              found fn pointer `fn() -> impl Future<Output = ()>`
 
-error[E0276]: impl has stricter requirements than trait
-  --> $DIR/fn-header-semantic-fail.rs:34:9
+error[E0053]: method `ft5` has an incompatible type for trait
+  --> $DIR/fn-header-semantic-fail.rs:34:48
    |
-LL |         const async unsafe extern "C" fn ft5();
-   |         --------------------------------------- definition of `ft5` from trait
-...
 LL |         const async unsafe extern "C" fn ft5() {}
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
+   |                                                ^
+   |                                                |
+   |                                                checked the `Output` of this `async fn`, found opaque type
+   |                                                expected `()`, found opaque type
+   |
+   = note: while checking the return type of the `async fn`
+note: type in trait
+  --> $DIR/fn-header-semantic-fail.rs:21:47
+   |
+LL |         const async unsafe extern "C" fn ft5();
+   |                                               ^
+   = note: expected fn pointer `unsafe extern "C" fn()`
+              found fn pointer `unsafe extern "C" fn() -> impl Future<Output = ()>`
 
 error[E0391]: cycle detected when computing type of `main::<impl at $DIR/fn-header-semantic-fail.rs:28:5: 28:17>::ft5::{opaque#0}`
   --> $DIR/fn-header-semantic-fail.rs:34:48
@@ -308,5 +326,5 @@ LL | | }
 
 error: aborting due to 23 previous errors
 
-Some errors have detailed explanations: E0276, E0379, E0391, E0706.
-For more information about an error, try `rustc --explain E0276`.
+Some errors have detailed explanations: E0053, E0379, E0391, E0706.
+For more information about an error, try `rustc --explain E0053`.
diff --git a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
index 6facc467f7a..aaf0f7eaef0 100644
--- a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
+++ b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.rs
@@ -14,7 +14,7 @@ trait B {
 impl B for A {
     async fn associated(); //~ ERROR without body
     //~^ ERROR cannot be declared `async`
-    //~| ERROR impl has stricter requirements than trait
+    //~| ERROR has an incompatible type for trait
 }
 
 fn main() {}
diff --git a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
index c144060a859..d3214458eac 100644
--- a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
+++ b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
@@ -44,16 +44,25 @@ LL |     async fn associated();
    = note: `async` trait functions are not currently supported
    = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
 
-error[E0276]: impl has stricter requirements than trait
-  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:5
+error[E0053]: method `associated` has an incompatible type for trait
+  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:15:26
    |
 LL |     async fn associated();
-   |     ---------------------- definition of `associated` from trait
-...
+   |                          ^
+   |                          |
+   |                          checked the `Output` of this `async fn`, found opaque type
+   |                          expected `()`, found opaque type
+   |
+   = note: while checking the return type of the `async fn`
+note: type in trait
+  --> $DIR/issue-70736-async-fn-no-body-def-collector.rs:11:26
+   |
 LL |     async fn associated();
-   |     ^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `(): Future`
+   |                          ^
+   = note: expected fn pointer `fn()`
+              found fn pointer `fn() -> impl Future<Output = ()>`
 
 error: aborting due to 6 previous errors
 
-Some errors have detailed explanations: E0276, E0706.
-For more information about an error, try `rustc --explain E0276`.
+Some errors have detailed explanations: E0053, E0706.
+For more information about an error, try `rustc --explain E0053`.
diff --git a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.rs b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.rs
index 377ce85e8b2..4a11bb5020e 100644
--- a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.rs
+++ b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.rs
@@ -3,7 +3,7 @@
 type Foo = impl Fn() -> Foo;
 
 fn foo() -> Foo {
-//~^ ERROR: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
+//~^ ERROR: overflow evaluating the requirement
     foo
 }
 
diff --git a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr
index d20b1cc6d85..00c682b2193 100644
--- a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr
+++ b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr
@@ -1,10 +1,8 @@
-error[E0275]: overflow evaluating the requirement `fn() -> Foo {foo}: Sized`
+error[E0275]: overflow evaluating the requirement `<fn() -> Foo {foo} as FnOnce<()>>::Output == fn() -> Foo {foo}`
   --> $DIR/issue-53398-cyclic-types.rs:5:13
    |
 LL | fn foo() -> Foo {
    |             ^^^
-   |
-   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_53398_cyclic_types`)
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/type-alias-impl-trait/issue-57961.rs b/src/test/ui/type-alias-impl-trait/issue-57961.rs
new file mode 100644
index 00000000000..472886c9caa
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-57961.rs
@@ -0,0 +1,18 @@
+#![feature(type_alias_impl_trait)]
+
+type X = impl Sized;
+
+trait Foo {
+    type Bar: Iterator<Item = X>;
+}
+
+impl Foo for () {
+    type Bar = std::vec::IntoIter<u32>;
+    //~^ ERROR type mismatch resolving `<std::vec::IntoIter<u32> as Iterator>::Item == X
+}
+
+fn incoherent() {
+    let f: X = 22_i32;
+}
+
+fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-57961.stderr b/src/test/ui/type-alias-impl-trait/issue-57961.stderr
new file mode 100644
index 00000000000..ed4caf6ce68
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-57961.stderr
@@ -0,0 +1,20 @@
+error[E0271]: type mismatch resolving `<std::vec::IntoIter<u32> as Iterator>::Item == X`
+  --> $DIR/issue-57961.rs:10:16
+   |
+LL | type X = impl Sized;
+   |          ---------- the expected opaque type
+...
+LL |     type Bar = std::vec::IntoIter<u32>;
+   |                ^^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found `u32`
+   |
+   = note: expected opaque type `X`
+                     found type `u32`
+note: required by a bound in `Foo::Bar`
+  --> $DIR/issue-57961.rs:6:24
+   |
+LL |     type Bar: Iterator<Item = X>;
+   |                        ^^^^^^^^ required by this bound in `Foo::Bar`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0271`.