cleaning up

Author: xonx4l

compiler/rustc_error_codes/src/error_codes/E0412.md

@@ -1,6 +1,64 @@
 #### Note: this error code is no longer emitted by the compiler.
 
-Unresolved types are now reported under the unified error code E0425
-("cannot find ... in this scope").
+Erroneous code examples:
 
-See the explanation for E0425 for guidance on common causes and fixes.
+```compile_fail,E0412
+impl Something {} // error: type name `Something` is not in scope
+
+// or:
+
+trait Foo {
+    fn bar(N); // error: type name `N` is not in scope
+}
+
+// or:
+
+fn foo(x: T) {} // type name `T` is not in scope
+```
+
+To fix this error, please verify you didn't misspell the type name, you did
+declare it or imported it into the scope. Examples:
+
+```
+struct Something;
+
+impl Something {} // ok!
+
+// or:
+
+trait Foo {
+    type N;
+
+    fn bar(_: Self::N); // ok!
+}
+
+// or:
+
+fn foo<T>(x: T) {} // ok!
+```
+
+Another case that causes this error is when a type is imported into a parent
+module. To fix this, you can follow the suggestion and use File directly or
+`use super::File;` which will import the types from the parent namespace. An
+example that causes this error is below:
+
+```compile_fail,E0412
+use std::fs::File;
+
+mod foo {
+    fn some_function(f: File) {}
+}
+```
+
+```
+use std::fs::File;
+
+mod foo {
+    // either
+    use super::File;
+    // or
+    // use std::fs::File;
+    fn foo(f: File) {}
+}
+# fn main() {} // don't insert it for us; that'll break imports
+```

compiler/rustc_resolve/src/late.rs

@@ -4359,7 +4359,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
                 // There are two different error messages user might receive at
                 // this point:
-                // - E0425 cannot find `{}` in this scope
+                // - E0425 cannot find type `{}` in this scope
                 // - E0433 failed to resolve: use of undeclared type or module `{}`
                 //
                 // The first one is emitted for paths in type-position, and the

tests/ui/parallel-rustc/ty-variance-issue-124423.stderr

@@ -283,4 +283,4 @@ note: if you're trying to build a new `Box<_, _>` consider using one of the foll
 error: aborting due to 30 previous errors
 
 Some errors have detailed explanations: E0121, E0224, E0261, E0425, E0599.
-For more information about an error, try `rustc --explain E0121`.
+For more information about an error, try `rustc --explain E0121`.