Improve -Wheader-hygiene to warn about using directives inside linkage

specifications within the global scope, from Elliot Glaysher.

llvm-svn: 128352

clang/lib/Sema/SemaDeclCXX.cpp

@@ -3817,6 +3817,19 @@ NamespaceDecl *Sema::getOrCreateStdNamespace() {
   return getStdNamespace();
 }
 
+/// \brief Determine whether a using statement is in a context where it will be
+/// apply in all contexts.
+static bool IsUsingDirectiveInToplevelContext(DeclContext *CurContext) {
+  switch (CurContext->getDeclKind()) {
+    case Decl::TranslationUnit:
+      return true;
+    case Decl::LinkageSpec:
+      return IsUsingDirectiveInToplevelContext(CurContext->getParent());
+    default:
+      return false;
+  }
+}
+
 Decl *Sema::ActOnUsingDirective(Scope *S,
                                           SourceLocation UsingLoc,
                                           SourceLocation NamespcLoc,
@@ -3902,7 +3915,7 @@ Decl *Sema::ActOnUsingDirective(Scope *S,
                                       SS.getWithLocInContext(Context),
                                       IdentLoc, Named, CommonAncestor);
 
-    if (CurContext->getDeclKind() == Decl::TranslationUnit &&
+    if (IsUsingDirectiveInToplevelContext(CurContext) &&
         !SourceMgr.isFromMainFile(IdentLoc)) {
       Diag(IdentLoc, diag::warn_using_directive_in_header);
     }

clang/test/SemaCXX/warn-using-namespace-in-header.cpp

@@ -7,3 +7,21 @@ using namespace dont_warn;
 
 // Warning is actually in the header but only the cpp file gets scanned.
 // expected-warning {{using namespace directive in global context in header}}
+
+
+
+
+
+
+
+
+
+// Warn inside linkage specs too.
+// expected-warning {{using namespace directive in global context in header}}
+
+
+
+
+
+
+// expected-warning {{using namespace directive in global context in header}}

clang/test/SemaCXX/warn-using-namespace-in-header.h

@@ -13,3 +13,30 @@ using namespace warn_in_header_in_global_context;
 namespace dont_warn_here {
 using namespace warn_in_header_in_global_context;
 }
+
+// We should warn in toplevel extern contexts.
+namespace warn_inside_linkage {}
+extern "C++" {
+using namespace warn_inside_linkage;
+}
+
+// This is really silly, but we should warn on it:
+extern "C++" {
+extern "C" {
+extern "C++" {
+using namespace warn_inside_linkage;
+}
+}
+}
+
+// But we shouldn't warn in extern contexts inside namespaces.
+namespace dont_warn_here {
+extern "C++" {
+using namespace warn_in_header_in_global_context;
+}
+}
+
+// We also shouldn't warn in case of functions.
+inline void foo() {
+  using namespace warn_in_header_in_global_context;
+}