Improve error message when duplicate names for type and trait method

src/librustc_typeck/check/method/mod.rs

@@ -58,8 +58,9 @@ pub enum MethodError<'tcx> {
     ClosureAmbiguity(// DefId of fn trait
                      DefId),
 
-    // Found an applicable method, but it is not visible.
-    PrivateMatch(Def),
+    // Found an applicable method, but it is not visible. The second argument contains a list of
+    // not-in-scope traits which may work.
+    PrivateMatch(Def, Vec<DefId>),
 
     // Found a `Self: Sized` bound where `Self` is a trait object, also the caller may have
     // forgotten to import a trait.

src/librustc_typeck/check/method/probe.rs

@@ -1015,7 +1015,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         };
 
         if let Some(def) = private_candidate {
-            return Err(MethodError::PrivateMatch(def));
+            return Err(MethodError::PrivateMatch(def, out_of_scope_traits));
         }
 
         Err(MethodError::NoMatch(NoMatchData::new(static_candidates,

src/librustc_typeck/check/method/suggest.rs

@@ -311,9 +311,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 self.sess().span_err(span, &msg);
             }
 
-            MethodError::PrivateMatch(def) => {
-                struct_span_err!(self.tcx.sess, span, E0624,
-                                 "{} `{}` is private", def.kind_name(), item_name).emit();
+            MethodError::PrivateMatch(def, out_of_scope_traits) => {
+                let mut err = struct_span_err!(self.tcx.sess, span, E0624,
+                                               "{} `{}` is private", def.kind_name(), item_name);
+                self.suggest_valid_traits(&mut err, out_of_scope_traits);
+                err.emit();
             }
 
             MethodError::IllegalSizedBound(candidates) => {
@@ -353,13 +355,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         err.note(&msg[..]);
     }
 
-    fn suggest_traits_to_import(&self,
-                                err: &mut DiagnosticBuilder,
-                                span: Span,
-                                rcvr_ty: Ty<'tcx>,
-                                item_name: ast::Name,
-                                rcvr_expr: Option<&hir::Expr>,
-                                valid_out_of_scope_traits: Vec<DefId>) {
+    fn suggest_valid_traits(&self,
+                            err: &mut DiagnosticBuilder,
+                            valid_out_of_scope_traits: Vec<DefId>) -> bool {
         if !valid_out_of_scope_traits.is_empty() {
             let mut candidates = valid_out_of_scope_traits;
             candidates.sort();
@@ -379,6 +377,20 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             });
 
             self.suggest_use_candidates(err, msg, candidates);
+            true
+        } else {
+            false
+        }
+    }
+
+    fn suggest_traits_to_import(&self,
+                                err: &mut DiagnosticBuilder,
+                                span: Span,
+                                rcvr_ty: Ty<'tcx>,
+                                item_name: ast::Name,
+                                rcvr_expr: Option<&hir::Expr>,
+                                valid_out_of_scope_traits: Vec<DefId>) {
+        if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
             return;
         }
 

src/librustc_typeck/check/mod.rs

@@ -4016,7 +4016,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             Ok(def) => def,
             Err(error) => {
                 let def = match error {
-                    method::MethodError::PrivateMatch(def) => def,
+                    method::MethodError::PrivateMatch(def, _) => def,
                     _ => Def::Err,
                 };
                 if item_name != keywords::Invalid.name() {

src/test/ui/trait-method-private.rs

@@ -0,0 +1,30 @@
+// Copyright 2017 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.
+
+mod inner {
+    pub trait Bar {
+        fn method(&self);
+    }
+
+    pub struct Foo;
+
+    impl Foo {
+        fn method(&self) {}
+    }
+
+    impl Bar for Foo {
+        fn method(&self) {}
+    }
+}
+
+fn main() {
+    let foo = inner::Foo;
+    foo.method();
+}

src/test/ui/trait-method-private.stderr

@@ -0,0 +1,12 @@
+error[E0624]: method `method` is private
+  --> $DIR/trait-method-private.rs:29:9
+   |
+29 |     foo.method();
+   |         ^^^^^^
+   |
+   = help: items from traits can only be used if the trait is in scope
+   = note: the following trait is implemented but not in scope, perhaps add a `use` for it:
+           candidate #1: `use inner::Bar;`
+
+error: aborting due to previous error
+