From 5ef122e9449a86e4a6466ea07ed7f5ba5f6a48bc Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Thu, 19 Mar 2009 22:01:50 +0000
Subject: [PATCH] Variables marked as "extern" can actually have internal
 linkage if there is a previous declaration marked "static". This fixes
 PR3645.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67336 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/AST/Decl.h    |  1 +
 lib/Sema/SemaDecl.cpp       | 17 ++++++++++++++---
 test/Sema/tentative-decls.c |  2 +-
 test/Sema/var-redecl.c      |  5 +++++
 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/clang/AST/Decl.h b/include/clang/AST/Decl.h
index d4d22060c8..e4a40c6caa 100644
--- a/include/clang/AST/Decl.h
+++ b/include/clang/AST/Decl.h
@@ -258,6 +258,7 @@ public:
   virtual void Destroy(ASTContext& C);
 
   StorageClass getStorageClass() const { return (StorageClass)SClass; }
+  void setStorageClass(StorageClass SC) { SClass = SC; }
 
   SourceLocation getTypeSpecStartLoc() const { return TypeSpecStartLoc; }
 
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 99ea707760..7c80fa553e 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -832,9 +832,20 @@ bool Sema::MergeVarDecl(VarDecl *New, Decl *OldD) {
     Diag(Old->getLocation(), diag::note_previous_definition);
     return true;
   }
-  // C99 6.2.2p4: Check if we have a non-static decl followed by a static.
-  if (New->getStorageClass() != VarDecl::Static &&
-      Old->getStorageClass() == VarDecl::Static) {
+  // C99 6.2.2p4: 
+  //   For an identifier declared with the storage-class specifier
+  //   extern in a scope in which a prior declaration of that
+  //   identifier is visible,23) if the prior declaration specifies
+  //   internal or external linkage, the linkage of the identifier at
+  //   the later declaration is the same as the linkage specified at
+  //   the prior declaration. If no prior declaration is visible, or
+  //   if the prior declaration specifies no linkage, then the
+  //   identifier has external linkage.
+  if ((New->hasExternalStorage() || New->getStorageClass() == VarDecl::None) &&
+      Old->hasLinkage())
+    /* Okay */;
+  else if (New->getStorageClass() != VarDecl::Static &&
+           Old->getStorageClass() == VarDecl::Static) {
     Diag(New->getLocation(), diag::err_non_static_static) << New->getDeclName();
     Diag(Old->getLocation(), diag::note_previous_definition);
     return true;
diff --git a/test/Sema/tentative-decls.c b/test/Sema/tentative-decls.c
index 23297f3a22..fc0d50086e 100644
--- a/test/Sema/tentative-decls.c
+++ b/test/Sema/tentative-decls.c
@@ -27,7 +27,7 @@ extern int i1; // expected-note {{previous definition is here}}
 static int i1; // expected-error{{static declaration of 'i1' follows non-static declaration}}
 
 static int i2 = 5; // expected-note 1 {{previous definition is here}}
-int i2 = 3; // expected-error{{non-static declaration of 'i2' follows static declaration}}
+int i2 = 3; // expected-error{{redefinition of 'i2'}}
 
 __private_extern__ int pExtern;
 int pExtern = 0;
diff --git a/test/Sema/var-redecl.c b/test/Sema/var-redecl.c
index 82ce58bcb9..037a8f136d 100644
--- a/test/Sema/var-redecl.c
+++ b/test/Sema/var-redecl.c
@@ -54,3 +54,8 @@ void g18(void) {
   extern int g19;
 }
 int *p=&g19; // expected-error{{use of undeclared identifier 'g19'}}
+
+// PR3645
+static int a;
+extern int a;
+int a;
-- 
2.40.0