Rollup merge of #65390 - GuillaumeGomez:long-err-explanation-E0576, r=matthewjasper,kinnison

Add long error explanation for E0576

Part of #61137.

Author: Centril

src/librustc_resolve/error_codes.rs

@@ -1797,6 +1797,31 @@ let _: <u8 as Age>::Empire; // ok!
 ```
 "##,
 
+E0576: r##"
+An associated item wasn't found in the given type.
+
+Erroneous code example:
+
+```compile_fail,E0576
+trait Hello {
+    type Who;
+
+    fn hello() -> <Self as Hello>::You; // error!
+}
+```
+
+In this example, we tried to use the non-existent associated type `You` of the
+`Hello` trait. To fix this error, use an existing associated type:
+
+```
+trait Hello {
+    type Who;
+
+    fn hello() -> <Self as Hello>::Who; // ok!
+}
+```
+"##,
+
 E0603: r##"
 A private item was used outside its scope.
 
@@ -1925,7 +1950,6 @@ struct Foo<X = Box<Self>> {
 //  E0427, merged into 530
 //  E0467, removed
 //  E0470, removed
-    E0576,
     E0577,
     E0578,
 }

src/test/ui/issues/issue-19883.stderr

@@ -6,3 +6,4 @@ LL |         <Dst as From<Self>>::Dst
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0576`.

src/test/ui/issues/issue-22037.stderr

@@ -6,3 +6,4 @@ LL |     fn a(&self) -> <Self as A>::X;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0576`.

src/test/ui/issues/issue-22384.stderr

@@ -6,3 +6,4 @@ LL |     <<i32 as Copy>::foobar as Trait>::foo();
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0576`.

src/test/ui/type/type-path-err-node-types.stderr

@@ -30,5 +30,5 @@ LL |     let _ = |a, b: _| -> _ { 0 };
 
 error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0282, E0412, E0425, E0433.
+Some errors have detailed explanations: E0282, E0412, E0425, E0433, E0576.
 For more information about an error, try `rustc --explain E0282`.

src/test/ui/ufcs/ufcs-partially-resolved.stderr

@@ -200,5 +200,5 @@ LL |     <u8 as Dr>::X::N;
 
 error: aborting due to 32 previous errors
 
-Some errors have detailed explanations: E0223, E0433, E0575, E0599.
+Some errors have detailed explanations: E0223, E0433, E0575, E0576, E0599.
 For more information about an error, try `rustc --explain E0223`.