Reject overloading of two static extern C functions.

This patch moves hasCLanguageLinkage to be VarDecl and FunctionDecl methods
so that they can be used from SemaOverload.cpp and then fixes the logic
in Sema::IsOverload.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171193 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 60 insertions, 29 deletions

diff --git a/include/clang/AST/Decl.h b/include/clang/AST/Decl.h
index bb75895df5..12b6c4a980 100644
--- a/include/clang/AST/Decl.h
+++ b/include/clang/AST/Decl.h
@@ -903,6 +903,12 @@ public:
   /// external, C linkage.
   bool isExternC() const;
 
+  /// Checks if this variable has C language linkage. Note that this is not the
+  /// same as isExternC since decls with non external linkage can have C
+  /// language linkage. They can also have C language linkage when they are not
+  /// declared in an extern C context, but a previous decl is.
+  bool hasCLanguageLinkage() const;
+
   /// isLocalVarDecl - Returns true for local variable declarations
   /// other than parameters.  Note that this includes static variables
   /// inside of functions. It also includes variables inside blocks.
@@ -1790,6 +1796,12 @@ public:
   /// external, C linkage.
   bool isExternC() const;
 
+  /// Checks if this function has C language linkage. Note that this is not the
+  /// same as isExternC since decls with non external linkage can have C
+  /// language linkage. They can also have C language linkage when they are not
+  /// declared in an extern C context, but a previous decl is.
+  bool hasCLanguageLinkage() const;
+
   /// \brief Determines whether this is a global function.
   bool isGlobal() const;
 
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 85ab002485..92b1e4abf2 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -1177,6 +1177,32 @@ SourceRange VarDecl::getSourceRange() const {
   return DeclaratorDecl::getSourceRange();
 }
 
+template<typename decl_type>
+static bool hasCLanguageLinkageTemplate(const decl_type &D) {
+  // Language linkage is a C++ concept, but saying that everything in C has
+  // C language linkage fits the implementation nicelly.
+  ASTContext &Context = D.getASTContext();
+  if (!Context.getLangOpts().CPlusPlus)
+    return true;
+
+  // dcl.link 4: A C language linkage is ignored in determining the language
+  // linkage of the names of class members and the function type of class member
+  // functions.
+  const DeclContext *DC = D.getDeclContext();
+  if (DC->isRecord())
+    return false;
+
+  // If the first decl is in an extern "C" context, any other redeclaration
+  // will have C language linkage. If the first one is not in an extern "C"
+  // context, we would have reported an error for any other decl being in one.
+  const decl_type *First = D.getFirstDeclaration();
+  return First->getDeclContext()->isExternCContext();
+}
+
+bool VarDecl::hasCLanguageLinkage() const {
+  return hasCLanguageLinkageTemplate(*this);
+}
+
 bool VarDecl::isExternC() const {
   if (getLinkage() != ExternalLinkage)
     return false;
@@ -1702,6 +1728,10 @@ bool FunctionDecl::isReservedGlobalPlacementOperator() const {
   return (proto->getArgType(1).getCanonicalType() == Context.VoidPtrTy);
 }
 
+bool FunctionDecl::hasCLanguageLinkage() const {
+  return hasCLanguageLinkageTemplate(*this);
+}
+
 bool FunctionDecl::isExternC() const {
   if (getLinkage() != ExternalLinkage)
     return false;
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 7c193e13bd..c9d0c7750c 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1969,32 +1969,6 @@ static bool isABIDefaultCC(Sema &S, CallingConv CC, FunctionDecl *D) {
   return ABIDefaultCC == CC;
 }
 
-/// Check if the given decl has C language linkage. Note that this is not
-/// the same as D.isExternC() since decls with non external linkage can have C
-/// language linkage. They can also have C language linkage when they are
-/// not declared in an extern C context, but a previous decl is.
-template<typename T>
-bool hasCLanguageLinkage(const T &D) {
-  // Language linkage is a C++ concept, but saying that everything in C has
-  // C language linkage fits the implementation nicelly.
-  ASTContext &Context = D.getASTContext();
-  if (!Context.getLangOpts().CPlusPlus)
-    return true;
-
-  // dcl.link 4: A C language linkage is ignored in determining the language
-  // linkage of the names of class members and the function type of class member
-  // functions.
-  const DeclContext *DC = D.getDeclContext();
-  if (DC->isRecord())
-    return false;
-
-  // If the first decl is in an extern "C" context, any other redeclaration
-  // will have C language linkage. If the first one is not in an extern "C"
-  // context, we would have reported an error for any other decl being in one.
-  const T *First = D.getFirstDeclaration();
-  return First->getDeclContext()->isExternCContext();
-}
-
 /// MergeFunctionDecl - We just parsed a function 'New' from
 /// declarator D which has the same name and scope as a previous
 /// declaration 'Old'.  Figure out how to resolve this situation,
@@ -2255,7 +2229,7 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, Scope *S) {
       assert(OldQTypeForComparison.isCanonical());
     }
 
-    if (!hasCLanguageLinkage(*Old) && hasCLanguageLinkage(*New)) {
+    if (!Old->hasCLanguageLinkage() && New->hasCLanguageLinkage()) {
       Diag(New->getLocation(), diag::err_different_language_linkage) << New;
       Diag(Old->getLocation(), PrevDiag);
       return true;
@@ -2645,7 +2619,7 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
     return;
   }
 
-  if (!hasCLanguageLinkage(*Old) && hasCLanguageLinkage(*New)) {
+  if (!Old->hasCLanguageLinkage() && New->hasCLanguageLinkage()) {
     Diag(New->getLocation(), diag::err_different_language_linkage) << New;
     Diag(Old->getLocation(), diag::note_previous_definition);
     New->setInvalidDecl();
diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 7ae6d9d5af..02584525c9 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -930,11 +930,19 @@ Sema::CheckOverload(Scope *S, FunctionDecl *New, const LookupResult &Old,
   return Ovl_Overload;
 }
 
+static bool canBeOverloaded(const FunctionDecl &D) {
+  if (D.getAttr<OverloadableAttr>())
+    return true;
+  if (D.hasCLanguageLinkage())
+    return false;
+  return true;
+}
+
 bool Sema::IsOverload(FunctionDecl *New, FunctionDecl *Old,
                       bool UseUsingDeclRules) {
   // If both of the functions are extern "C", then they are not
   // overloads.
-  if (Old->isExternC() && New->isExternC())
+  if (!canBeOverloaded(*Old) && !canBeOverloaded(*New))
     return false;
 
   FunctionTemplateDecl *OldTemplate = Old->getDescribedFunctionTemplate();
diff --git a/test/SemaCXX/linkage2.cpp b/test/SemaCXX/linkage2.cpp
index ccf32008f1..f6561b9f12 100644
--- a/test/SemaCXX/linkage2.cpp
+++ b/test/SemaCXX/linkage2.cpp
@@ -11,3 +11,10 @@ namespace test1 {
     void f(); // expected-error {{declaration of 'f' has a different language linkage}}
   }
 }
+
+extern "C" {
+  static void test2_f() { // expected-note {{previous definition is here}}
+  }
+  static void test2_f(int x) { // expected-error {{conflicting types for 'test2_f'}}
+  }
+}