[Sema] Formatting warnings should see through Objective-C message sends

This commit improves the '-Wformat' warnings by ensuring that the formatting
checker can see through Objective-C message sends when we are calling an
Objective-C method with an appropriate format_arg attribute.

rdar://23622446

Differential Revision: https://reviews.llvm.org/D25820

llvm-svn: 284961

clang/lib/Sema/SemaChecking.cpp

@@ -4479,6 +4479,20 @@ checkFormatStringExpr(Sema &S, const Expr *E, ArrayRef<const Expr *> Args,
 
     return SLCT_NotALiteral;
   }
+  case Stmt::ObjCMessageExprClass: {
+    const auto *ME = cast<ObjCMessageExpr>(E);
+    if (const auto *ND = ME->getMethodDecl()) {
+      if (const auto *FA = ND->getAttr<FormatArgAttr>()) {
+        unsigned ArgIndex = FA->getFormatIdx();
+        const Expr *Arg = ME->getArg(ArgIndex - 1);
+        return checkFormatStringExpr(
+            S, Arg, Args, HasVAListArg, format_idx, firstDataArg, Type,
+            CallType, InFunctionCall, CheckedVarArgs, UncoveredArg, Offset);
+      }
+    }
+
+    return SLCT_NotALiteral;
+  }
   case Stmt::ObjCStringLiteralClass:
   case Stmt::StringLiteralClass: {
     const StringLiteral *StrE = nullptr;

clang/test/SemaObjC/format-strings-objc.m

@@ -264,3 +264,41 @@ void testObjCModifierFlags() {
   NSLog(@"%2$[tt]@ %1$[tt]@", @"Foo", @"Bar"); // no-warning
   NSLog(@"%2$[tt]@ %1$[tt]s", @"Foo", @"Bar"); // expected-warning {{object format flags cannot be used with 's' conversion specifier}}
 }
+
+// rdar://23622446
+@interface RD23622446_Tester: NSObject
+
++ (void)stringWithFormat:(const char *)format, ... __attribute__((format(__printf__, 1, 2)));
+
+@end
+
+@implementation RD23622446_Tester
+
+__attribute__ ((format_arg(1)))
+const char *rd23622446(const char *format) {
+  return format;
+}
+
++ (void)stringWithFormat:(const char *)format, ... {
+  return;
+}
+
+- (const char *)test:(const char *)format __attribute__ ((format_arg(1))) {
+  return format;
+}
+
+- (NSString *)str:(NSString *)format __attribute__ ((format_arg(1))) {
+  return format;
+}
+
+- (void)foo {
+  [RD23622446_Tester stringWithFormat:rd23622446("%u"), 1, 2]; // expected-warning {{data argument not used by format string}}
+  [RD23622446_Tester stringWithFormat:[self test: "%u"], 1, 2]; // expected-warning {{data argument not used by format string}}
+  [RD23622446_Tester stringWithFormat:[self test: "%s %s"], "name"]; // expected-warning {{more '%' conversions than data arguments}}
+  NSLog([self str: @"%@ %@"], @"name"); // expected-warning {{more '%' conversions than data arguments}}
+  [RD23622446_Tester stringWithFormat:rd23622446("%d"), 1]; // ok
+  [RD23622446_Tester stringWithFormat:[self test: "%d %d"], 1, 2]; // ok
+  NSLog([self str: @"%@"], @"string"); // ok
+}
+
+@end