Sema: An extern declaration can't be a redeclaration of a parameter

In the following:
void f(int x) { extern int x; }

The second declaration of 'x' shouldn't be considered a redeclaration of
the parameter.

This is a different approach to r225780.

llvm-svn: 225875

clang/include/clang/AST/Decl.h

@@ -906,6 +906,11 @@ public:
     return false;
   }
 
+  /// \brief Similar to isLocalVarDecl but also includes parameters.
+  bool isLocalVarDeclOrParm() const {
+    return isLocalVarDecl() || getKind() == Decl::ParmVar;
+  }
+
   /// isFunctionOrMethodVarDecl - Similar to isLocalVarDecl, but
   /// excludes variables declared in blocks.
   bool isFunctionOrMethodVarDecl() const {

clang/lib/Sema/SemaDecl.cpp

@@ -3285,12 +3285,12 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
 
   // Check if extern is followed by non-extern and vice-versa.
   if (New->hasExternalStorage() &&
-      !Old->hasLinkage() && Old->isLocalVarDecl()) {
+      !Old->hasLinkage() && Old->isLocalVarDeclOrParm()) {
     Diag(New->getLocation(), diag::err_extern_non_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);
     return New->setInvalidDecl();
   }
-  if (Old->hasLinkage() && New->isLocalVarDecl() &&
+  if (Old->hasLinkage() && New->isLocalVarDeclOrParm() &&
       !New->hasExternalStorage()) {
     Diag(New->getLocation(), diag::err_non_extern_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);

clang/test/Sema/var-redecl.c

@@ -60,3 +60,7 @@ int *p=&g19; // expected-error{{use of undeclared identifier 'g19'}} \
 static int a;
 extern int a; // expected-note {{previous declaration is here}}
 int a;	// expected-error {{non-static declaration of 'a' follows static declaration}}
+
+void f(int x) { // expected-note {{previous definition is here}}
+  extern int x; // expected-error {{extern declaration of 'x' follows non-extern declaration}}
+}