auto merge of #7844 : huonw/rust/no-implicit-prelude, r=alexcrichton

It disables the insertion of `use std::prelude::*;` into the top of
all the modules below the item on which it is placed (including that
item itself).

(Similar to GHC's `-XNoImplicitPrelude`.)

src/test/compile-fail/no-implicit-prelude-nested.rs

@@ -0,0 +1,68 @@
+// Copyright 2013 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.
+
+// Test that things from the prelude aren't in scope. Use many of them
+// so that renaming some things won't magically make this test fail
+// for the wrong reason (e.g. if `Add` changes to `Addition`, and
+// `no_implicit_prelude` stops working, then the `impl Add` will still
+// fail with the same error message).
+
+#[no_implicit_prelude]
+mod foo {
+    mod baz {
+        struct Test;
+        impl Add for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Clone for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Iterator for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl ToStr for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Writer for Test {} //~ ERROR: attempt to implement a nonexistent trait
+
+        fn foo() {
+            print("foo"); //~ ERROR: unresolved name
+            println("bar"); //~ ERROR: unresolved name
+        }
+    }
+
+    struct Test;
+    impl Add for Test {} //~ ERROR: attempt to implement a nonexistent trait
+    impl Clone for Test {} //~ ERROR: attempt to implement a nonexistent trait
+    impl Iterator for Test {} //~ ERROR: attempt to implement a nonexistent trait
+    impl ToStr for Test {} //~ ERROR: attempt to implement a nonexistent trait
+    impl Writer for Test {} //~ ERROR: attempt to implement a nonexistent trait
+
+    fn foo() {
+        print("foo"); //~ ERROR: unresolved name
+        println("bar"); //~ ERROR: unresolved name
+    }
+}
+
+fn qux() {
+    #[no_implicit_prelude]
+    mod qux_inner {
+        struct Test;
+        impl Add for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Clone for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Iterator for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl ToStr for Test {} //~ ERROR: attempt to implement a nonexistent trait
+        impl Writer for Test {} //~ ERROR: attempt to implement a nonexistent trait
+
+        fn foo() {
+            print("foo"); //~ ERROR: unresolved name
+            println("bar"); //~ ERROR: unresolved name
+        }
+    }
+}
+
+
+fn main() {
+    // these should work fine
+    print("foo");
+    println("bar");
+}

src/test/compile-fail/no-implicit-prelude.rs

@@ -0,0 +1,29 @@
+// Copyright 2013 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.
+
+#[no_implicit_prelude];
+
+// Test that things from the prelude aren't in scope. Use many of them
+// so that renaming some things won't magically make this test fail
+// for the wrong reason (e.g. if `Add` changes to `Addition`, and
+// `no_implicit_prelude` stops working, then the `impl Add` will still
+// fail with the same error message).
+
+struct Test;
+impl Add for Test {} //~ ERROR: attempt to implement a nonexistent trait
+impl Clone for Test {} //~ ERROR: attempt to implement a nonexistent trait
+impl Iterator for Test {} //~ ERROR: attempt to implement a nonexistent trait
+impl ToStr for Test {} //~ ERROR: attempt to implement a nonexistent trait
+impl Writer for Test {} //~ ERROR: attempt to implement a nonexistent trait
+
+fn main() {
+    print("foo"); //~ ERROR: unresolved name
+    println("bar"); //~ ERROR: unresolved name
+}