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

llvm-svn: 150260

clang/lib/Sema/SemaChecking.cpp

@@ -1381,6 +1381,7 @@ bool Sema::SemaCheckStringLiteral(const Expr *E, Expr **Args,
                                  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

clang/test/SemaCXX/format-strings.cpp

@@ -39,3 +39,14 @@ void h(int *i) {
   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}}
+}