Implement dcl.link paragraph 5.

The language linkage of redeclarations must match. GCC was already reporting
an error for this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171139 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 0 deletions

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index e1d772b084..7c193e13bd 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1969,6 +1969,32 @@ 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,
@@ -2229,6 +2255,12 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, Scope *S) {
       assert(OldQTypeForComparison.isCanonical());
     }
 
+    if (!hasCLanguageLinkage(*Old) && hasCLanguageLinkage(*New)) {
+      Diag(New->getLocation(), diag::err_different_language_linkage) << New;
+      Diag(Old->getLocation(), PrevDiag);
+      return true;
+    }
+
     if (OldQTypeForComparison == NewQType)
       return MergeCompatibleFunctionDecls(New, Old, S);
 
@@ -2612,6 +2644,14 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
     New->setInvalidDecl();
     return;
   }
+
+  if (!hasCLanguageLinkage(*Old) && hasCLanguageLinkage(*New)) {
+    Diag(New->getLocation(), diag::err_different_language_linkage) << New;
+    Diag(Old->getLocation(), diag::note_previous_definition);
+    New->setInvalidDecl();
+    return;
+  }
+
   // c99 6.2.2 P4.
   // For an identifier declared with the storage-class specifier extern in a
   // scope in which a prior declaration of that identifier is visible, if