Show detailed expected/found types in error message when trait paths are the same

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -2060,14 +2060,24 @@ fn values_str(
                     expected: exp_found.expected.print_only_trait_path(),
                     found: exp_found.found.print_only_trait_path(),
                 };
-                self.expected_found_str(pretty_exp_found)
+                match self.expected_found_str(pretty_exp_found) {
+                    Some((expected, found)) if expected == found => {
+                        self.expected_found_str(exp_found)
+                    }
+                    ret => ret,
+                }
             }
             infer::PolyTraitRefs(exp_found) => {
                 let pretty_exp_found = ty::error::ExpectedFound {
                     expected: exp_found.expected.print_only_trait_path(),
                     found: exp_found.found.print_only_trait_path(),
                 };
-                self.expected_found_str(pretty_exp_found)
+                match self.expected_found_str(pretty_exp_found) {
+                    Some((expected, found)) if expected == found => {
+                        self.expected_found_str(exp_found)
+                    }
+                    ret => ret,
+                }
             }
         }
     }

src/test/ui/error-codes/E0308-2.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL | impl Eq for &dyn DynEq {}
    |      ^^ lifetime mismatch
    |
-   = note: expected trait `PartialEq`
+   = note: expected trait `<&dyn DynEq as PartialEq>`
-              found trait `PartialEq`
+              found trait `<&(dyn DynEq + 'static) as PartialEq>`
 note: the lifetime `'_` as defined on the impl at 9:13...
   --> $DIR/E0308-2.rs:9:13
    |

src/test/ui/issues/issue-20831-debruijn.stderr

@@ -19,8 +19,8 @@ note: ...so that the types are compatible
    |
 LL |     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
    |        ^^^^^^^^^
-   = note: expected `Publisher<'_>`
+   = note: expected `<MyStruct<'a> as Publisher<'_>>`
-              found `Publisher<'_>`
+              found `<MyStruct<'_> as Publisher<'_>>`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-65230.rs

@@ -0,0 +1,19 @@
+trait T {
+    type U;
+    fn f(&self) -> Self::U;
+}
+
+struct X<'a>(&'a mut i32);
+
+impl<'a> T for X<'a> {
+    type U = &'a i32;
+    fn f(&self) -> Self::U {
+        self.0
+    }
+    //~^^^ ERROR cannot infer an appropriate lifetime for lifetime parameter `'a`
+    //
+    // Return type of `f` has lifetime `'a` but it tries to return `self.0` which
+    // has lifetime `'_`.
+}
+
+fn main() {}

src/test/ui/issues/issue-65230.stderr

@@ -0,0 +1,38 @@
+error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
+  --> $DIR/issue-65230.rs:10:28
+   |
+LL |       fn f(&self) -> Self::U {
+   |  ____________________________^
+LL | |         self.0
+LL | |     }
+   | |_____^
+   |
+note: first, the lifetime cannot outlive the anonymous lifetime defined on the method body at 10:10...
+  --> $DIR/issue-65230.rs:10:10
+   |
+LL |     fn f(&self) -> Self::U {
+   |          ^^^^^
+note: ...so that reference does not outlive borrowed content
+  --> $DIR/issue-65230.rs:11:9
+   |
+LL |         self.0
+   |         ^^^^^^
+note: but, the lifetime must be valid for the lifetime `'a` as defined on the impl at 8:6...
+  --> $DIR/issue-65230.rs:8:6
+   |
+LL | impl<'a> T for X<'a> {
+   |      ^^
+note: ...so that the types are compatible
+  --> $DIR/issue-65230.rs:10:28
+   |
+LL |       fn f(&self) -> Self::U {
+   |  ____________________________^
+LL | |         self.0
+LL | |     }
+   | |_____^
+   = note: expected `<X<'a> as T>`
+              found `<X<'_> as T>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/issue-50716.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     let _x = *s;
    |         ^^ lifetime mismatch
    |
-   = note: expected type `Sized`
+   = note: expected type `<<&'a T as A>::X as Sized>`
-              found type `Sized`
+              found type `<<&'static T as A>::X as Sized>`
 note: the lifetime `'a` as defined on the function body at 9:8...
   --> $DIR/issue-50716.rs:9:8
    |

src/test/ui/variance/variance-contravariant-self-trait-match.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'min G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'min G as Get>`
-              found type `Get`
+              found type `<&'max G as Get>`
 note: the lifetime `'min` as defined on the function body at 10:21...
   --> $DIR/variance-contravariant-self-trait-match.rs:10:21
    |
@@ -23,8 +23,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'max G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'max G as Get>`
-              found type `Get`
+              found type `<&'min G as Get>`
 note: the lifetime `'min` as defined on the function body at 16:21...
   --> $DIR/variance-contravariant-self-trait-match.rs:16:21
    |

src/test/ui/variance/variance-covariant-self-trait-match.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'min G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'min G as Get>`
-              found type `Get`
+              found type `<&'max G as Get>`
 note: the lifetime `'min` as defined on the function body at 10:21...
   --> $DIR/variance-covariant-self-trait-match.rs:10:21
    |
@@ -23,8 +23,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'max G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'max G as Get>`
-              found type `Get`
+              found type `<&'min G as Get>`
 note: the lifetime `'min` as defined on the function body at 17:21...
   --> $DIR/variance-covariant-self-trait-match.rs:17:21
    |

src/test/ui/variance/variance-invariant-self-trait-match.stderr

@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'min G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'min G as Get>`
-              found type `Get`
+              found type `<&'max G as Get>`
 note: the lifetime `'min` as defined on the function body at 7:21...
   --> $DIR/variance-invariant-self-trait-match.rs:7:21
    |
@@ -23,8 +23,8 @@ error[E0308]: mismatched types
 LL |     impls_get::<&'max G>();
    |     ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected type `Get`
+   = note: expected type `<&'max G as Get>`
-              found type `Get`
+              found type `<&'min G as Get>`
 note: the lifetime `'min` as defined on the function body at 13:21...
   --> $DIR/variance-invariant-self-trait-match.rs:13:21
    |