Better diagnostics when mismatched types due to implict static lifetime

src/test/ui/generic-associated-types/issue-78113-lifetime-mismatch-dyn-trait-box.rs

@@ -0,0 +1,19 @@
+// Test for diagnostics when we have mismatched lifetime due to implict 'static lifetime in GATs
+
+// check-fail
+
+#![feature(generic_associated_types)]
+
+pub trait A {}
+impl A for &dyn A {}
+impl A for Box<dyn A> {}
+
+pub trait B {
+    type T<'a>: A;
+}
+
+impl B for () {
+    type T<'a> = Box<dyn A + 'a>; //~ incompatible lifetime on type
+}
+
+fn main() {}

src/test/ui/generic-associated-types/issue-78113-lifetime-mismatch-dyn-trait-box.stderr

@@ -0,0 +1,28 @@
+error: incompatible lifetime on type
+  --> $DIR/issue-78113-lifetime-mismatch-dyn-trait-box.rs:16:5
+   |
+LL |     type T<'a> = Box<dyn A + 'a>;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: because this has an unmet lifetime requirement
+  --> $DIR/issue-78113-lifetime-mismatch-dyn-trait-box.rs:12:17
+   |
+LL |     type T<'a>: A;
+   |                 ^ introduces a `'static` lifetime requirement
+note: ...the lifetime `'a` as defined on the associated item at 16:12...
+  --> $DIR/issue-78113-lifetime-mismatch-dyn-trait-box.rs:16:12
+   |
+LL |     type T<'a> = Box<dyn A + 'a>;
+   |            ^^
+note: ...does not necessarily outlive the static lifetime introduced by the compatible `impl`
+  --> $DIR/issue-78113-lifetime-mismatch-dyn-trait-box.rs:9:20
+   |
+LL | impl A for Box<dyn A> {}
+   |                    ^ this has an implicit `'static` lifetime requirement
+help: consider relaxing the implicit `'static` requirement
+   |
+LL | impl A for Box<dyn A + '_> {}
+   |                      ^^^^
+
+error: aborting due to previous error
+

src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.rs

@@ -13,5 +13,5 @@ pub struct Ref<'a>(&'a u8);
 impl Trait for Ref {} //~ ERROR:  implicit elided lifetime not allowed here
 
 extern "C" {
-    pub fn repro(_: Wrapper<Ref>); //~ ERROR: mismatched types
+    pub fn repro(_: Wrapper<Ref>); //~ ERROR: incompatible lifetime on type
 }

src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr

@@ -4,21 +4,22 @@ error[E0726]: implicit elided lifetime not allowed here
 LL | impl Trait for Ref {}
    |                ^^^- help: indicate the anonymous lifetime: `<'_>`
 
-error[E0308]: mismatched types
+error: incompatible lifetime on type
   --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:16:21
    |
 LL |     pub fn repro(_: Wrapper<Ref>);
-   |                     ^^^^^^^^^^^^ lifetime mismatch
+   |                     ^^^^^^^^^^^^
    |
-   = note: expected trait `Trait`
-              found trait `Trait`
-note: the anonymous lifetime #1 defined on the method body at 16:5...
+note: because this has an unmet lifetime requirement
+  --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:8:23
+   |
+LL | pub struct Wrapper<T: Trait>(T);
+   |                       ^^^^^ introduces a `'static` lifetime requirement
+note: ...the anonymous lifetime #1 defined on the method body at 16:5...
   --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:16:5
    |
 LL |     pub fn repro(_: Wrapper<Ref>);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: ...does not necessarily outlive the static lifetime
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.