Fix incorrect outer function type parameter message

src/librustc_resolve/lib.rs

@@ -198,12 +198,25 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver,
 
             let cm = resolver.session.source_map();
             match outer_def {
-                Def::SelfTy(_, maybe_impl_defid) => {
-                    if let Some(impl_span) = maybe_impl_defid.map_or(None,
-                            |def_id| resolver.definitions.opt_span(def_id)) {
-                        err.span_label(reduce_impl_span_to_impl_keyword(cm, impl_span),
-                                    "`Self` type implicitly declared here, on the `impl`");
+                Def::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
+                    if let Some(impl_span) = maybe_impl_defid.and_then(|def_id| {
+                        resolver.definitions.opt_span(def_id)
+                    }) {
+                        err.span_label(
+                            reduce_impl_span_to_impl_keyword(cm, impl_span),
+                            "`Self` type implicitly declared here, by this `impl`",
+                        );
+                    }
+                    match (maybe_trait_defid, maybe_impl_defid) {
+                        (Some(_), None) => {
+                            err.span_label(span, "can't use `Self` here");
+                        }
+                        (_, Some(_)) => {
+                            err.span_label(span, "use a type here instead");
+                        }
+                        (None, None) => bug!("`impl` without trait nor type?"),
                     }
+                    return err;
                 },
                 Def::TyParam(typaram_defid) => {
                     if let Some(typaram_span) = resolver.definitions.opt_span(typaram_defid) {

src/test/ui/error-codes/E0401.stderr

@@ -24,12 +24,13 @@ error[E0401]: can't use type parameters from outer function
   --> $DIR/E0401.rs:32:25
    |
 LL | impl<T> Iterator for A<T> {
-   | ---- `Self` type implicitly declared here, on the `impl`
+   | ---- `Self` type implicitly declared here, by this `impl`
 ...
 LL |         fn helper(sel: &Self) -> u8 { //~ ERROR E0401
-   |            ------       ^^^^ use of type variable from outer function
-   |            |
-   |            help: try using a local type parameter instead: `helper<Self>`
+   |                         ^^^^
+   |                         |
+   |                         use of type variable from outer function
+   |                         use a type here instead
 
 error: aborting due to 3 previous errors
 

src/test/ui/issues/issue-12796.stderr

@@ -2,9 +2,10 @@ error[E0401]: can't use type parameters from outer function
   --> $DIR/issue-12796.rs:13:22
    |
 LL |         fn inner(_: &Self) {
-   |            -----     ^^^^ use of type variable from outer function
-   |            |
-   |            help: try using a local type parameter instead: `inner<Self>`
+   |                      ^^^^
+   |                      |
+   |                      use of type variable from outer function
+   |                      can't use `Self` here
 
 error: aborting due to previous error
 

src/test/ui/use-self-in-inner-fn.rs

@@ -0,0 +1,24 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct A;
+
+impl A {
+//~^ NOTE `Self` type implicitly declared here, by this `impl`
+    fn banana(&mut self) {
+        fn peach(this: &Self) {
+        //~^ ERROR can't use type parameters from outer function
+        //~| NOTE use of type variable from outer function
+        //~| NOTE use a type here instead
+        }
+    }
+}
+
+fn main() {}

src/test/ui/use-self-in-inner-fn.stderr

@@ -0,0 +1,15 @@
+error[E0401]: can't use type parameters from outer function
+  --> $DIR/use-self-in-inner-fn.rs:16:25
+   |
+LL | impl A {
+   | ---- `Self` type implicitly declared here, by this `impl`
+...
+LL |         fn peach(this: &Self) {
+   |                         ^^^^
+   |                         |
+   |                         use of type variable from outer function
+   |                         use a type here instead
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0401`.