librustc: Disallow modules and types from having the same name.

This will break code that looks like:

    struct Foo {
        ...
    }

    mod Foo {
        ...
    }

Change this code to:

    struct Foo {
        ...
    }

    impl Foo {
        ...
    }

Or rename the module.

Closes #15205.

[breaking-change]

src/librustc/middle/resolve.rs

@@ -307,7 +307,7 @@ enum BareIdentifierPatternResolution {
 #[deriving(PartialEq)]
 enum DuplicateCheckingMode {
     ForbidDuplicateModules,
-    ForbidDuplicateTypes,
+    ForbidDuplicateTypesAndModules,
     ForbidDuplicateValues,
     ForbidDuplicateTypesAndValues,
     OverwriteDuplicates
@@ -792,10 +792,9 @@ impl PrimitiveTypeTable {
 
 fn namespace_error_to_str(ns: NamespaceError) -> &'static str {
     match ns {
-        NoError     => "",
-        ModuleError => "module",
-        TypeError   => "type",
-        ValueError  => "value",
+        NoError                 => "",
+        ModuleError | TypeError => "type or module",
+        ValueError              => "value",
     }
 }
 
@@ -1033,9 +1032,12 @@ impl<'a> Resolver<'a> {
                         }
                         Some(TypeNS)
                     }
-                    ForbidDuplicateTypes => {
+                    ForbidDuplicateTypesAndModules => {
                         match child.def_for_namespace(TypeNS) {
-                            Some(DefMod(_)) | None => {}
+                            None => {}
+                            Some(_) if child.get_module_if_available()
+                                            .map(|m| m.kind.get()) ==
+                                       Some(ImplModuleKind) => {}
                             Some(_) => duplicate_type = TypeError
                         }
                         Some(TypeNS)
@@ -1177,7 +1179,10 @@ impl<'a> Resolver<'a> {
             // These items live in the type namespace.
             ItemTy(..) => {
                 let name_bindings =
-                    self.add_child(ident, parent.clone(), ForbidDuplicateTypes, sp);
+                    self.add_child(ident,
+                                   parent.clone(),
+                                   ForbidDuplicateTypesAndModules,
+                                   sp);
 
                 name_bindings.define_type
                     (DefTy(local_def(item.id)), sp, is_public);
@@ -1186,7 +1191,10 @@ impl<'a> Resolver<'a> {
 
             ItemEnum(ref enum_definition, _) => {
                 let name_bindings =
-                    self.add_child(ident, parent.clone(), ForbidDuplicateTypes, sp);
+                    self.add_child(ident,
+                                   parent.clone(),
+                                   ForbidDuplicateTypesAndModules,
+                                   sp);
 
                 name_bindings.define_type
                     (DefTy(local_def(item.id)), sp, is_public);
@@ -1206,7 +1214,7 @@ impl<'a> Resolver<'a> {
                 // Adding to both Type and Value namespaces or just Type?
                 let (forbid, ctor_id) = match struct_def.ctor_id {
                     Some(ctor_id)   => (ForbidDuplicateTypesAndValues, Some(ctor_id)),
-                    None            => (ForbidDuplicateTypes, None)
+                    None            => (ForbidDuplicateTypesAndModules, None)
                 };
 
                 let name_bindings = self.add_child(ident, parent.clone(), forbid, sp);
@@ -1327,7 +1335,10 @@ impl<'a> Resolver<'a> {
 
             ItemTrait(_, _, _, ref methods) => {
                 let name_bindings =
-                    self.add_child(ident, parent.clone(), ForbidDuplicateTypes, sp);
+                    self.add_child(ident,
+                                   parent.clone(),
+                                   ForbidDuplicateTypesAndModules,
+                                   sp);
 
                 // Add all the methods within to a new module.
                 let parent_link = self.get_parent_link(parent.clone(), ident);

src/test/compile-fail/dup-struct-enum-struct-variant.rs

@@ -11,9 +11,9 @@
 #![feature(struct_variant)]
 
 enum Foo { C { a: int, b: int } }
-struct C { a: int, b: int }         //~ ERROR error: duplicate definition of type `C`
+struct C { a: int, b: int }         //~ ERROR error: duplicate definition of type or module `C`
 
 struct A { x: int }
-enum Bar { A { x: int } }           //~ ERROR error: duplicate definition of type `A`
+enum Bar { A { x: int } }           //~ ERROR error: duplicate definition of type or module `A`
 
 fn main() {}

src/test/compile-fail/enum-and-module-in-same-scope.rs

@@ -0,0 +1,19 @@
+// Copyright 2014 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 Foo {
+    pub static X: int = 42;
+}
+
+enum Foo {  //~ ERROR duplicate definition of type or module `Foo`
+    X
+}
+
+fn main() {}

src/test/compile-fail/issue-3099-a.rs

@@ -10,6 +10,6 @@
 
 enum a { b, c }
 
-enum a { d, e } //~ ERROR duplicate definition of type `a`
+enum a { d, e } //~ ERROR duplicate definition of type or module `a`
 
 fn main() {}

src/test/compile-fail/issue-3099-b.rs

@@ -10,6 +10,6 @@
 
 pub mod a {}
 
-pub mod a {} //~ ERROR duplicate definition of module `a`
+pub mod a {} //~ ERROR duplicate definition of type or module `a`
 
 fn main() {}