Implement RFC 2128 (use_nested_groups)

This commit adds support for nested groups inside `use` declarations,
such as `use foo::{bar, sub::{baz::Foo, *}};`.

src/test/compile-fail/absolute-paths-in-nested-use-groups.rs

@@ -0,0 +1,22 @@
+// 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.
+
+#![feature(use_nested_groups)]
+#![allow(unused_imports)]
+
+mod foo {}
+
+use foo::{
+    ::bar,       //~ ERROR crate root in paths can only be used in start position
+    super::bar,  //~ ERROR `super` in paths can only be used in start position
+    self::bar,   //~ ERROR `self` in paths can only be used in start position
+};
+
+fn main() {}

src/test/compile-fail/feature-gate-use_nested_groups.rs

@@ -0,0 +1,31 @@
+// 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.
+
+#![allow(unused_imports, dead_code)]
+
+mod a {
+    pub enum B {}
+    pub enum C {}
+
+    pub mod d {
+        pub enum E {}
+        pub enum F {}
+
+        pub mod g {
+            pub enum H {}
+        }
+    }
+}
+
+use a::{B, d::{*, g::H}};  //~ ERROR glob imports in `use` groups are experimental
+                           //~^ ERROR nested groups in `use` are experimental
+                           //~^^ ERROR paths in `use` groups are experimental
+
+fn main() {}

src/test/run-pass/use-nested-groups.rs

@@ -0,0 +1,35 @@
+// 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.
+
+#![feature(use_nested_groups)]
+
+mod a {
+    pub enum B {}
+
+    pub mod d {
+        pub enum E {}
+        pub enum F {}
+
+        pub mod g {
+            pub enum H {}
+            pub enum I {}
+        }
+    }
+}
+
+use a::{B, d::{self, *, g::H}};
+
+fn main() {
+    let _: B;
+    let _: E;
+    let _: F;
+    let _: H;
+    let _: d::g::I;
+}

src/test/ui/owl-import-generates-unused-import-lint.rs

@@ -0,0 +1,22 @@
+// 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.
+
+#![feature(use_nested_groups)]
+#![deny(unused_imports)]
+
+mod foo {
+    pub enum Bar {}
+}
+
+use foo::{*, *}; //~ ERROR unused import: `*`
+
+fn main() {
+    let _: Bar;
+}

src/test/ui/owl-import-generates-unused-import-lint.stderr

@@ -0,0 +1,14 @@
+error: unused import: `*`
+  --> $DIR/owl-import-generates-unused-import-lint.rs:18:14
+   |
+18 | use foo::{*, *}; //~ ERROR unused import: `*`
+   |              ^
+   |
+note: lint level defined here
+  --> $DIR/owl-import-generates-unused-import-lint.rs:12:9
+   |
+12 | #![deny(unused_imports)]
+   |         ^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/similar-tokens.rs

@@ -14,6 +14,6 @@ mod x {
 }
 
 // `.` is similar to `,` so list parsing should continue to closing `}`
-use x::{A. B}; //~ ERROR expected one of `,` or `as`, found `.`
+use x::{A. B}; //~ ERROR expected one of `,`, `::`, or `as`, found `.`
 
 fn main() {}

src/test/ui/similar-tokens.stderr

@@ -1,8 +1,8 @@
-error: expected one of `,` or `as`, found `.`
+error: expected one of `,`, `::`, or `as`, found `.`
   --> $DIR/similar-tokens.rs:17:10
    |
-17 | use x::{A. B}; //~ ERROR expected one of `,` or `as`, found `.`
-   |          ^ expected one of `,` or `as` here
+17 | use x::{A. B}; //~ ERROR expected one of `,`, `::`, or `as`, found `.`
+   |          ^ expected one of `,`, `::`, or `as` here
 
 error: aborting due to previous error