[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

1 files changed, 14 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 501f93ed629..fd8e19876b9 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/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;