Index: cfe/trunk/lib/Format/Format.cpp
===================================================================
--- cfe/trunk/lib/Format/Format.cpp
+++ cfe/trunk/lib/Format/Format.cpp
@@ -32,6 +32,7 @@
 #include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Lex/Lexer.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Path.h"
@@ -40,6 +41,7 @@
 #include <algorithm>
 #include <memory>
 #include <string>
+#include <unordered_set>
 
 #define DEBUG_TYPE "format-formatter"
 
@@ -48,6 +50,16 @@
 LLVM_YAML_IS_SEQUENCE_VECTOR(clang::format::FormatStyle::IncludeCategory)
 LLVM_YAML_IS_SEQUENCE_VECTOR(clang::format::FormatStyle::RawStringFormat)
 
+namespace std {
+// Allow using StringRef in std::unordered_set.
+template <> struct hash<llvm::StringRef> {
+public:
+  size_t operator()(const llvm::StringRef &s) const {
+    return llvm::hash_value(s);
+  }
+};
+} // namespace std
+
 namespace llvm {
 namespace yaml {
 template <> struct ScalarEnumerationTraits<FormatStyle::LanguageKind> {
@@ -1400,6 +1412,101 @@
   std::set<FormatToken *, FormatTokenLess> DeletedTokens;
 };
 
+class ObjCHeaderStyleGuesser : public TokenAnalyzer {
+public:
+  ObjCHeaderStyleGuesser(const Environment &Env, const FormatStyle &Style)
+      : TokenAnalyzer(Env, Style), IsObjC(false) {}
+
+  std::pair<tooling::Replacements, unsigned>
+  analyze(TokenAnnotator &Annotator,
+          SmallVectorImpl<AnnotatedLine *> &AnnotatedLines,
+          FormatTokenLexer &Tokens) override {
+    assert(Style.Language == FormatStyle::LK_Cpp);
+    IsObjC = guessIsObjC(AnnotatedLines, Tokens.getKeywords());
+    tooling::Replacements Result;
+    return {Result, 0};
+  }
+
+  bool isObjC() { return IsObjC; }
+
+private:
+  static bool guessIsObjC(const SmallVectorImpl<AnnotatedLine *> &AnnotatedLines,
+                          const AdditionalKeywords &Keywords) {
+    static const std::unordered_set<StringRef> FoundationIdentifiers = {
+        "CGFloat",
+        "NSAffineTransform",
+        "NSArray",
+        "NSAttributedString",
+        "NSCache",
+        "NSCharacterSet",
+        "NSCountedSet",
+        "NSData",
+        "NSDataDetector",
+        "NSDecimal",
+        "NSDecimalNumber",
+        "NSDictionary",
+        "NSEdgeInsets",
+        "NSHashTable",
+        "NSIndexPath",
+        "NSIndexSet",
+        "NSInteger",
+        "NSLocale",
+        "NSMapTable",
+        "NSMutableArray",
+        "NSMutableAttributedString",
+        "NSMutableCharacterSet",
+        "NSMutableData",
+        "NSMutableDictionary",
+        "NSMutableIndexSet",
+        "NSMutableOrderedSet",
+        "NSMutableSet",
+        "NSMutableString",
+        "NSNumber",
+        "NSNumberFormatter",
+        "NSOrderedSet",
+        "NSPoint",
+        "NSPointerArray",
+        "NSRange",
+        "NSRect",
+        "NSRegularExpression",
+        "NSSet",
+        "NSSize",
+        "NSString",
+        "NSUInteger",
+        "NSURL",
+        "NSURLComponents",
+        "NSURLQueryItem",
+        "NSUUID",
+    };
+
+    for (auto &Line : AnnotatedLines) {
+      for (FormatToken *FormatTok = Line->First->Next; FormatTok;
+           FormatTok = FormatTok->Next) {
+        if ((FormatTok->Previous->is(tok::at) &&
+             (FormatTok->isObjCAtKeyword(tok::objc_interface) ||
+              FormatTok->isObjCAtKeyword(tok::objc_implementation) ||
+              FormatTok->isObjCAtKeyword(tok::objc_protocol) ||
+              FormatTok->isObjCAtKeyword(tok::objc_end) ||
+              FormatTok->isOneOf(tok::numeric_constant, tok::l_square,
+                                 tok::l_brace))) ||
+            (FormatTok->Tok.isAnyIdentifier() &&
+             FoundationIdentifiers.find(FormatTok->TokenText) !=
+                 FoundationIdentifiers.end()) ||
+            FormatTok->is(TT_ObjCStringLiteral) ||
+            FormatTok->isOneOf(Keywords.kw_NS_ENUM, Keywords.kw_NS_OPTIONS,
+                               TT_ObjCBlockLBrace, TT_ObjCBlockLParen,
+                               TT_ObjCDecl, TT_ObjCForIn, TT_ObjCMethodExpr,
+                               TT_ObjCMethodSpecifier, TT_ObjCProperty)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  bool IsObjC;
+};
+
 struct IncludeDirective {
   StringRef Filename;
   StringRef Text;
@@ -2185,14 +2292,15 @@
   FormatStyle Style = getLLVMStyle();
   Style.Language = getLanguageByFileName(FileName);
 
-  // This is a very crude detection of whether a header contains ObjC code that
-  // should be improved over time and probably be done on tokens, not one the
-  // bare content of the file.
-  if (Style.Language == FormatStyle::LK_Cpp && FileName.endswith(".h") &&
-      (Code.contains("\n- (") || Code.contains("\n+ (") ||
-       Code.contains("\n@end\n") || Code.contains("\n@end ") ||
-       Code.endswith("@end")))
-    Style.Language = FormatStyle::LK_ObjC;
+  if (Style.Language == FormatStyle::LK_Cpp && FileName.endswith(".h")) {
+    std::unique_ptr<Environment> Env =
+        Environment::CreateVirtualEnvironment(Code, FileName, /*Ranges=*/{});
+    ObjCHeaderStyleGuesser Guesser(*Env, Style);
+    Guesser.process();
+    if (Guesser.isObjC()) {
+      Style.Language = FormatStyle::LK_ObjC;
+    }
+  }
 
   FormatStyle FallbackStyle = getNoStyle();
   if (!getPredefinedStyle(FallbackStyleName, Style.Language, &FallbackStyle))
Index: cfe/trunk/unittests/Format/FormatTestObjC.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTestObjC.cpp
+++ cfe/trunk/unittests/Format/FormatTestObjC.cpp
@@ -94,6 +94,66 @@
   Style = getStyle("LLVM", "a.h", "none", "void f() {}");
   ASSERT_TRUE((bool)Style);
   EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none", "@interface Foo\n@end\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none",
+                   "const int interface = 1;\nconst int end = 2;\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none", "@protocol Foo\n@end\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none",
+                   "const int protocol = 1;\nconst int end = 2;\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none", "extern NSString *kFoo;\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style =
+      getStyle("{}", "a.h", "none", "typedef NS_ENUM(NSInteger, Foo) {};\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none", "enum Foo {};");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none", "extern NSInteger Foo();\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style =
+      getStyle("{}", "a.h", "none", "inline void Foo() { Log(@\"Foo\"); }\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style =
+      getStyle("{}", "a.h", "none", "inline void Foo() { Log(\"Foo\"); }\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
+
+  Style =
+      getStyle("{}", "a.h", "none", "inline void Foo() { id = @[1, 2, 3]; }\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none",
+                   "inline void Foo() { id foo = @{1: 2, 3: 4, 5: 6}; }\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_ObjC, Style->Language);
+
+  Style = getStyle("{}", "a.h", "none",
+                   "inline void Foo() { int foo[] = {1, 2, 3}; }\n");
+  ASSERT_TRUE((bool)Style);
+  EXPECT_EQ(FormatStyle::LK_Cpp, Style->Language);
 }
 
 TEST_F(FormatTestObjC, FormatObjCTryCatch) {