Enhance checking for null format string literal to take into account __null.   Fixes <rdar://problem/8269537>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150260 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index a44633d..be32688 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -1381,6 +1381,7 @@
                                  inFunctionCall);
   }
 
+  case Stmt::GNUNullExprClass:
   case Stmt::IntegerLiteralClass:
     // Technically -Wformat-nonliteral does not warn about this case.
     // The behavior of printf and friends in this case is implementation
diff --git a/test/SemaCXX/format-strings.cpp b/test/SemaCXX/format-strings.cpp
index 8b0b00d..456167d 100644
--- a/test/SemaCXX/format-strings.cpp
+++ b/test/SemaCXX/format-strings.cpp
@@ -39,3 +39,14 @@
   printf(foo.gettext("%d"), i); // expected-warning{{format specifies type 'int' but the argument has type 'int *'}}
   printf(Foo::gettext_static("%d"), i); // expected-warning{{format specifies type 'int' but the argument has type 'int *'}}
 }
+
+// Test handling __null for format string literal checking.
+extern "C" {
+  int test_null_format(const char *format, ...) __attribute__((__format__ (__printf__, 1, 2)));
+}
+
+void rdar8269537(const char *f)
+{
+  test_null_format(__null); // no-warning
+  test_null_format(f); // expected-warning {{not a string literal}}
+}