Rollup merge of rust-lang#47512 - GuillaumeGomez:e0659, r=petrochenkov

Add E0659 for ambiguous names

Still on the tracks of the "no error without error code" road.

src/librustc_resolve/diagnostics.rs

@@ -1621,6 +1621,59 @@ println!("const value: {}", SomeModule::PRIVATE); // ok!
 ```
 "##,
 
+E0659: r##"
+An item usage is ambiguous.
+
+Erroneous code example:
+
+```compile_fail,E0659
+pub mod moon {
+    pub fn foo() {}
+}
+
+pub mod earth {
+    pub fn foo() {}
+}
+
+mod collider {
+    pub use moon::*;
+    pub use earth::*;
+}
+
+fn main() {
+    collider::foo(); // ERROR: `foo` is ambiguous
+}
+```
+
+This error generally appears when two items with the same name are imported into
+a module. Here, the `foo` functions are imported and reexported from the
+`collider` module and therefore, when we're using `collider::foo()`, both
+functions collide.
+
+To solve this error, the best solution is generally to keep the path before the
+item when using it. Example:
+
+```
+pub mod moon {
+    pub fn foo() {}
+}
+
+pub mod earth {
+    pub fn foo() {}
+}
+
+mod collider {
+    pub use moon;
+    pub use earth;
+}
+
+fn main() {
+    collider::moon::foo(); // ok!
+    collider::earth::foo(); // ok!
+}
+```
+"##,
+
 }
 
 register_diagnostics! {

src/librustc_resolve/lib.rs

@@ -3802,7 +3802,7 @@ impl<'a> Resolver<'a> {
                 self.session.buffer_lint(lint::builtin::LEGACY_IMPORTS, id, span, &msg);
             } else {
                 let mut err =
-                    self.session.struct_span_err(span, &format!("`{}` is ambiguous", name));
+                    struct_span_err!(self.session, span, E0659, "`{}` is ambiguous", name);
                 err.span_note(b1.span, &msg1);
                 match b2.def() {
                     Def::Macro(..) if b2.span == DUMMY_SP =>

src/test/compile-fail/E0659.rs

@@ -0,0 +1,26 @@
+// 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.
+
+mod moon {
+    pub fn foo() {}
+}
+
+mod earth {
+    pub fn foo() {}
+}
+
+mod collider {
+    pub use moon::*;
+    pub use earth::*;
+}
+
+fn main() {
+    collider::foo(); //~ ERROR E0659
+}

src/test/ui/imports/duplicate.stderr

@@ -12,7 +12,7 @@ help: You can use `as` to change the binding name of the import
 25 |     use a::foo as Otherfoo; //~ ERROR the name `foo` is defined multiple times
    |         ^^^^^^^^^^^^^^^^^^
 
-error: `foo` is ambiguous
+error[E0659]: `foo` is ambiguous
   --> $DIR/duplicate.rs:56:9
    |
 56 |     use self::foo::bar; //~ ERROR `foo` is ambiguous
@@ -30,7 +30,7 @@ note: `foo` could also refer to the name imported here
    |         ^^^^^^^^^^^
    = note: consider adding an explicit import of `foo` to disambiguate
 
-error: `foo` is ambiguous
+error[E0659]: `foo` is ambiguous
   --> $DIR/duplicate.rs:45:5
    |
 45 |     f::foo(); //~ ERROR `foo` is ambiguous
@@ -48,7 +48,7 @@ note: `foo` could also refer to the name imported here
    |             ^^^^
    = note: consider adding an explicit import of `foo` to disambiguate
 
-error: `foo` is ambiguous
+error[E0659]: `foo` is ambiguous
   --> $DIR/duplicate.rs:46:5
    |
 46 |     g::foo(); //~ ERROR `foo` is ambiguous
@@ -66,7 +66,7 @@ note: `foo` could also refer to the name imported here
    |             ^^^^
    = note: consider adding an explicit import of `foo` to disambiguate
 
-error: `foo` is ambiguous
+error[E0659]: `foo` is ambiguous
   --> $DIR/duplicate.rs:59:9
    |
 59 |         foo::bar(); //~ ERROR `foo` is ambiguous

src/test/ui/imports/macro-paths.stderr

@@ -1,4 +1,4 @@
-error: `bar` is ambiguous
+error[E0659]: `bar` is ambiguous
   --> $DIR/macro-paths.rs:25:5
    |
 25 |     bar::m! { //~ ERROR ambiguous
@@ -16,7 +16,7 @@ note: `bar` could also refer to the name imported here
    |         ^^^^^^
    = note: macro-expanded items do not shadow when used in a macro invocation path
 
-error: `baz` is ambiguous
+error[E0659]: `baz` is ambiguous
   --> $DIR/macro-paths.rs:35:5
    |
 35 |     baz::m! { //~ ERROR ambiguous

src/test/ui/imports/macros.stderr

@@ -15,7 +15,7 @@ note: `m` could also refer to the macro imported here
 49 |     use two_macros::m;
    |         ^^^^^^^^^^^^^
 
-error: `m` is ambiguous
+error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:28:5
    |
 28 |     m! { //~ ERROR ambiguous
@@ -33,7 +33,7 @@ note: `m` could also refer to the name imported here
    |         ^^^^^^^^^^^^^
    = note: macro-expanded macro imports do not shadow
 
-error: `m` is ambiguous
+error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:41:9
    |
 41 |         m! { //~ ERROR ambiguous

src/test/ui/imports/shadow_builtin_macros.stderr

@@ -9,7 +9,7 @@ error: `panic` is already in scope
    |
    = note: macro-expanded `macro_rules!`s may not shadow existing macros (see RFC 1560)
 
-error: `panic` is ambiguous
+error[E0659]: `panic` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:27:14
    |
 27 |     fn f() { panic!(); } //~ ERROR ambiguous
@@ -23,7 +23,7 @@ note: `panic` could refer to the name imported here
    = note: `panic` is also a builtin macro
    = note: consider adding an explicit import of `panic` to disambiguate
 
-error: `panic` is ambiguous
+error[E0659]: `panic` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:32:14
    |
 32 |     fn f() { panic!(); } //~ ERROR ambiguous
@@ -37,7 +37,7 @@ note: `panic` could refer to the name imported here
    = note: `panic` is also a builtin macro
    = note: macro-expanded macro imports do not shadow
 
-error: `n` is ambiguous
+error[E0659]: `n` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:61:5
    |
 61 |     n!(); //~ ERROR ambiguous