Do not allow a module and tuple struct of the same name to coexist.

Fixes rust-lang#21546.

Author: Nick Hamann

src/librustc_resolve/build_reduced_graph.rs

@@ -67,6 +67,7 @@ enum DuplicateCheckingMode {
     ForbidDuplicateTypesAndModules,
     ForbidDuplicateValues,
     ForbidDuplicateTypesAndValues,
+    ForbidDuplicateTypesModulesValues,
     OverwriteDuplicates
 }
 
@@ -202,6 +203,18 @@ impl<'a, 'b:'a, 'tcx:'b> GraphBuilder<'a, 'b, 'tcx> {
                         }
                         n
                     }
+                    ForbidDuplicateTypesModulesValues => {
+                        let mut n = None;
+                        if child.defined_in_namespace(TypeNS) {
+                            duplicate_type = TypeError;
+                            n = Some(TypeNS);
+                        }
+                        if child.defined_in_namespace(ValueNS) {
+                            duplicate_type = ValueError;
+                            n = Some(ValueNS);
+                        }
+                        n
+                    }
                     OverwriteDuplicates => None
                 };
                 if duplicate_type != NoError {
@@ -480,7 +493,7 @@ impl<'a, 'b:'a, 'tcx:'b> GraphBuilder<'a, 'b, 'tcx> {
             ItemStruct(ref struct_def, _) => {
                 // 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)),
+                    Some(ctor_id)   => (ForbidDuplicateTypesModulesValues, Some(ctor_id)),
                     None            => (ForbidDuplicateTypesAndModules, None)
                 };
 

src/test/run-pass/issue-14564.rs src/test/compile-fail/issue-21546.rs

@@ -8,8 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// Also works as a test for #14564
+
 mod Foo { }
+//~^ NOTE first definition of type or module
+
 struct Foo;
+//~^ ERROR duplicate definition of type or module `Foo`
+
 impl Foo { }
 
 fn main() { }