llvm · tstellar · Mar 4, 2025 · Feb 22, 2025
diff --git a/clang/docs/ClangFormatStyleOptions.rst b/clang/docs/ClangFormatStyleOptions.rst
@@ -4735,15 +4735,24 @@ the configuration (without a prefix: ``Auto``).
 .. _Language:
 
 **Language** (``LanguageKind``) :versionbadge:`clang-format 3.5` :ref:`¶ <Language>`
-  Language, this format style is targeted at.
+  The language that this format style targets.
+
+  .. note::
+
+   You can specify the language (``C``, ``Cpp``, or ``ObjC``) for ``.h``
+   files by adding a ``// clang-format Language:`` line before the first
+   non-comment (and non-empty) line, e.g. ``// clang-format Language: Cpp``.
 
   Possible values:
 
   * ``LK_None`` (in configuration: ``None``)
     Do not use.
 
+  * ``LK_C`` (in configuration: ``C``)
+    Should be used for C.
+
   * ``LK_Cpp`` (in configuration: ``Cpp``)
-    Should be used for C, C++.
+    Should be used for C++.
 
   * ``LK_CSharp`` (in configuration: ``CSharp``)
     Should be used for C#.

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -1358,6 +1358,10 @@ clang-format
 - Adds ``WrapNamespaceBodyWithEmptyLines`` option.
 - Adds the ``IndentExportBlock`` option.
 - Adds ``PenaltyBreakBeforeMemberAccess`` option.
+- Add the C language instead of treating it like C++.
+- Allow specifying the language (C, C++, or Objective-C) for a ``.h`` file by
+  adding a special comment (e.g. ``// clang-format Language: ObjC``) near the
+  top of the file.
 
 libclang
 --------

diff --git a/clang/include/clang/Format/Format.h b/clang/include/clang/Format/Format.h
@@ -3275,7 +3275,9 @@ struct FormatStyle {
   enum LanguageKind : int8_t {
     /// Do not use.
     LK_None,
-    /// Should be used for C, C++.
+    /// Should be used for C.
+    LK_C,
+    /// Should be used for C++.
     LK_Cpp,
     /// Should be used for C#.
     LK_CSharp,
@@ -3300,7 +3302,9 @@ struct FormatStyle {
     /// https://sci-hub.st/10.1109/IEEESTD.2018.8299595
     LK_Verilog
   };
-  bool isCpp() const { return Language == LK_Cpp || Language == LK_ObjC; }
+  bool isCpp() const {
+    return Language == LK_Cpp || Language == LK_C || Language == LK_ObjC;
+  }
   bool isCSharp() const { return Language == LK_CSharp; }
   bool isJson() const { return Language == LK_Json; }
   bool isJavaScript() const { return Language == LK_JavaScript; }
@@ -3310,7 +3314,12 @@ struct FormatStyle {
   }
   bool isTableGen() const { return Language == LK_TableGen; }
 
-  /// Language, this format style is targeted at.
+  /// The language that this format style targets.
+  /// \note
+  ///  You can specify the language (``C``, ``Cpp``, or ``ObjC``) for ``.h``
+  ///  files by adding a ``// clang-format Language:`` line before the first
+  ///  non-comment (and non-empty) line, e.g. ``// clang-format Language: Cpp``.
+  /// \endnote
   /// \version 3.5
   LanguageKind Language;
 
@@ -5665,6 +5674,8 @@ FormatStyle::LanguageKind guessLanguage(StringRef FileName, StringRef Code);
 // Returns a string representation of ``Language``.
 inline StringRef getLanguageName(FormatStyle::LanguageKind Language) {
   switch (Language) {
+  case FormatStyle::LK_C:
+    return "C";
   case FormatStyle::LK_Cpp:
     return "C++";
   case FormatStyle::LK_CSharp:

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
@@ -401,6 +401,7 @@ template <> struct MappingTraits<FormatStyle::KeepEmptyLinesStyle> {
 
 template <> struct ScalarEnumerationTraits<FormatStyle::LanguageKind> {
   static void enumeration(IO &IO, FormatStyle::LanguageKind &Value) {
+    IO.enumCase(Value, "C", FormatStyle::LK_C);
     IO.enumCase(Value, "Cpp", FormatStyle::LK_Cpp);
     IO.enumCase(Value, "Java", FormatStyle::LK_Java);
     IO.enumCase(Value, "JavaScript", FormatStyle::LK_JavaScript);
@@ -3952,7 +3953,12 @@ LangOptions getFormattingLangOpts(const FormatStyle &Style) {
   LangOpts.Digraphs = LexingStd >= FormatStyle::LS_Cpp11;
 
   LangOpts.LineComment = 1;
-  LangOpts.CXXOperatorNames = Style.isCpp();
+
+  const auto Language = Style.Language;
+  LangOpts.C17 = Language == FormatStyle::LK_C;
+  LangOpts.CXXOperatorNames =
+      Language == FormatStyle::LK_Cpp || Language == FormatStyle::LK_ObjC;
+
   LangOpts.Bool = 1;
   LangOpts.ObjC = 1;
   LangOpts.MicrosoftExt = 1;    // To get kw___try, kw___finally.
@@ -3977,6 +3983,8 @@ const char *StyleOptionHelpDescription =
     "   --style=\"{BasedOnStyle: llvm, IndentWidth: 8}\"";
 
 static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
+  if (FileName.ends_with(".c"))
+    return FormatStyle::LK_C;
   if (FileName.ends_with(".java"))
     return FormatStyle::LK_Java;
   if (FileName.ends_with_insensitive(".js") ||
@@ -4016,6 +4024,35 @@ static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
   return FormatStyle::LK_Cpp;
 }
 
+static FormatStyle::LanguageKind getLanguageByComment(const Environment &Env) {
+  const auto ID = Env.getFileID();
+  const auto &SourceMgr = Env.getSourceManager();
+
+  LangOptions LangOpts;
+  LangOpts.CPlusPlus = 1;
+  LangOpts.LineComment = 1;
+
+  Lexer Lex(ID, SourceMgr.getBufferOrFake(ID), SourceMgr, LangOpts);
+  Lex.SetCommentRetentionState(true);
+
+  for (Token Tok; !Lex.LexFromRawLexer(Tok) && Tok.is(tok::comment);) {
+    auto Text = StringRef(SourceMgr.getCharacterData(Tok.getLocation()),
+                          Tok.getLength());
+    if (!Text.consume_front("// clang-format Language:"))
+      continue;
+
+    Text = Text.trim();
+    if (Text == "C")
+      return FormatStyle::LK_C;
+    if (Text == "Cpp")
+      return FormatStyle::LK_Cpp;
+    if (Text == "ObjC")
+      return FormatStyle::LK_ObjC;
+  }
+
+  return FormatStyle::LK_None;
+}
+
 FormatStyle::LanguageKind guessLanguage(StringRef FileName, StringRef Code) {
   const auto GuessedLanguage = getLanguageByFileName(FileName);
   if (GuessedLanguage == FormatStyle::LK_Cpp) {
@@ -4025,6 +4062,10 @@ FormatStyle::LanguageKind guessLanguage(StringRef FileName, StringRef Code) {
     if (!Code.empty() && (Extension.empty() || Extension == ".h")) {
       auto NonEmptyFileName = FileName.empty() ? "guess.h" : FileName;
       Environment Env(Code, NonEmptyFileName, /*Ranges=*/{});
+      if (const auto Language = getLanguageByComment(Env);
+          Language != FormatStyle::LK_None) {
+        return Language;
+      }
       ObjCHeaderStyleGuesser Guesser(Env, getLLVMStyle());
       Guesser.process();
       if (Guesser.isObjC())

diff --git a/clang/lib/Format/FormatToken.cpp b/clang/lib/Format/FormatToken.cpp
@@ -42,11 +42,11 @@ static SmallVector<StringRef> CppNonKeywordTypes = {
 };
 
 bool FormatToken::isTypeName(const LangOptions &LangOpts) const {
-  const bool IsCpp = LangOpts.CXXOperatorNames;
-  return is(TT_TypeName) || Tok.isSimpleTypeSpecifier(LangOpts) ||
-         (IsCpp && is(tok::identifier) &&
-          std::binary_search(CppNonKeywordTypes.begin(),
-                             CppNonKeywordTypes.end(), TokenText));
+  if (is(TT_TypeName) || Tok.isSimpleTypeSpecifier(LangOpts))
+    return true;
+  return (LangOpts.CXXOperatorNames || LangOpts.C17) && is(tok::identifier) &&
+         std::binary_search(CppNonKeywordTypes.begin(),
+                            CppNonKeywordTypes.end(), TokenText);
 }
 
 bool FormatToken::isTypeOrIdentifier(const LangOptions &LangOpts) const {

diff --git a/clang/lib/Format/FormatToken.h b/clang/lib/Format/FormatToken.h
@@ -743,29 +743,6 @@ struct FormatToken {
     return isOneOf(tok::star, tok::amp, tok::ampamp);
   }
 
-  bool isCppAlternativeOperatorKeyword() const {
-    assert(!TokenText.empty());
-    if (!isalpha(TokenText[0]))
-      return false;
-
-    switch (Tok.getKind()) {
-    case tok::ampamp:
-    case tok::ampequal:
-    case tok::amp:
-    case tok::pipe:
-    case tok::tilde:
-    case tok::exclaim:
-    case tok::exclaimequal:
-    case tok::pipepipe:
-    case tok::pipeequal:
-    case tok::caret:
-    case tok::caretequal:
-      return true;
-    default:
-      return false;
-    }
-  }
-
   bool isUnaryOperator() const {
     switch (Tok.getKind()) {
     case tok::plus:

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
@@ -129,7 +129,7 @@ class AnnotatingParser {
       : Style(Style), Line(Line), CurrentToken(Line.First), AutoFound(false),
         IsCpp(Style.isCpp()), LangOpts(getFormattingLangOpts(Style)),
         Keywords(Keywords), Scopes(Scopes), TemplateDeclarationDepth(0) {
-    assert(IsCpp == LangOpts.CXXOperatorNames);
+    assert(IsCpp == (LangOpts.CXXOperatorNames || LangOpts.C17));
     Contexts.push_back(Context(tok::unknown, 1, /*IsExpression=*/false));
     resetTokenMetadata();
   }
@@ -3820,7 +3820,7 @@ static bool isFunctionDeclarationName(const LangOptions &LangOpts,
   };
 
   const auto *Next = Current.Next;
-  const bool IsCpp = LangOpts.CXXOperatorNames;
+  const bool IsCpp = LangOpts.CXXOperatorNames || LangOpts.C17;
 
   // Find parentheses of parameter list.
   if (Current.is(tok::kw_operator)) {

diff --git a/clang/lib/Format/TokenAnnotator.h b/clang/lib/Format/TokenAnnotator.h
@@ -225,7 +225,7 @@ class TokenAnnotator {
   TokenAnnotator(const FormatStyle &Style, const AdditionalKeywords &Keywords)
       : Style(Style), IsCpp(Style.isCpp()),
         LangOpts(getFormattingLangOpts(Style)), Keywords(Keywords) {
-    assert(IsCpp == LangOpts.CXXOperatorNames);
+    assert(IsCpp == (LangOpts.CXXOperatorNames || LangOpts.C17));
   }
 
   /// Adapts the indent levels of comment lines to the indent of the

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -168,7 +168,7 @@ UnwrappedLineParser::UnwrappedLineParser(
                        : IG_Inited),
       IncludeGuardToken(nullptr), FirstStartColumn(FirstStartColumn),
       Macros(Style.Macros, SourceMgr, Style, Allocator, IdentTable) {
-  assert(IsCpp == LangOpts.CXXOperatorNames);
+  assert(IsCpp == (LangOpts.CXXOperatorNames || LangOpts.C17));
 }
 
 void UnwrappedLineParser::reset() {
@@ -1712,12 +1712,6 @@ void UnwrappedLineParser::parseStructuralElement(
            OpeningBrace && OpeningBrace->isOneOf(TT_RequiresExpressionLBrace,
                                                  TT_CompoundRequirementLBrace);
        !eof();) {
-    if (IsCpp && FormatTok->isCppAlternativeOperatorKeyword()) {
-      if (auto *Next = Tokens->peekNextToken(/*SkipComment=*/true);
-          Next && Next->isBinaryOperator()) {
-        FormatTok->Tok.setKind(tok::identifier);
-      }
-    }
     const FormatToken *Previous = FormatTok->Previous;
     switch (FormatTok->Tok.getKind()) {
     case tok::at:

diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
@@ -17784,9 +17784,11 @@ TEST_F(FormatTest, ConfigurableSpaceBeforeAssignmentOperators) {
   verifyFormat("int a = 5;");
   verifyFormat("a += 42;");
   verifyFormat("a or_eq 8;");
-  verifyFormat("xor = foo;");
 
-  FormatStyle Spaces = getLLVMStyle();
+  auto Spaces = getLLVMStyle(FormatStyle::LK_C);
+  verifyFormat("xor = foo;", Spaces);
+
+  Spaces.Language = FormatStyle::LK_Cpp;
   Spaces.SpaceBeforeAssignmentOperators = false;
   verifyFormat("int a= 5;", Spaces);
   verifyFormat("a+= 42;", Spaces);
@@ -24683,6 +24685,7 @@ TEST_F(FormatTest, StructuredBindings) {
 }
 
 TEST_F(FormatTest, FileAndCode) {
+  EXPECT_EQ(FormatStyle::LK_C, guessLanguage("foo.c", ""));
   EXPECT_EQ(FormatStyle::LK_Cpp, guessLanguage("foo.cc", ""));
   EXPECT_EQ(FormatStyle::LK_ObjC, guessLanguage("foo.m", ""));
   EXPECT_EQ(FormatStyle::LK_ObjC, guessLanguage("foo.mm", ""));
@@ -24848,6 +24851,18 @@ TEST_F(FormatTest, GuessLanguageWithChildLines) {
       guessLanguage("foo.h", "#define FOO ({ foo(); ({ NSString *s; }) })"));
 }
 
+TEST_F(FormatTest, GetLanguageByComment) {
+  EXPECT_EQ(FormatStyle::LK_C,
+            guessLanguage("foo.h", "// clang-format Language: C\n"
+                                   "int i;"));
+  EXPECT_EQ(FormatStyle::LK_Cpp,
+            guessLanguage("foo.h", "// clang-format Language: Cpp\n"
+                                   "int DoStuff(CGRect rect);"));
+  EXPECT_EQ(FormatStyle::LK_ObjC,
+            guessLanguage("foo.h", "// clang-format Language: ObjC\n"
+                                   "int i;"));
+}
+
 TEST_F(FormatTest, TypenameMacros) {
   std::vector<std::string> TypenameMacros = {"STACK_OF", "LIST", "TAILQ_ENTRY"};
 

diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -3646,6 +3646,11 @@ TEST_F(TokenAnnotatorTest, CppAltOperatorKeywords) {
   ASSERT_EQ(Tokens.size(), 7u) << Tokens;
   EXPECT_TOKEN(Tokens[3], tok::pipepipe, TT_BinaryOperator);
 
+  Tokens = annotate("return segment < *this or *this < segment;");
+  ASSERT_EQ(Tokens.size(), 12u) << Tokens;
+  EXPECT_TOKEN(Tokens[5], tok::pipepipe, TT_BinaryOperator);
+  EXPECT_TOKEN(Tokens[6], tok::star, TT_UnaryOperator);
+
   Tokens = annotate("a = b or_eq c;");
   ASSERT_EQ(Tokens.size(), 7u) << Tokens;
   EXPECT_TOKEN(Tokens[3], tok::pipeequal, TT_BinaryOperator);
@@ -3658,11 +3663,13 @@ TEST_F(TokenAnnotatorTest, CppAltOperatorKeywords) {
   ASSERT_EQ(Tokens.size(), 7u) << Tokens;
   EXPECT_TOKEN(Tokens[3], tok::caretequal, TT_BinaryOperator);
 
-  Tokens = annotate("xor = foo;");
+  const auto StyleC = getLLVMStyle(FormatStyle::LK_C);
+
+  Tokens = annotate("xor = foo;", StyleC);
   ASSERT_EQ(Tokens.size(), 5u) << Tokens;
   EXPECT_TOKEN(Tokens[0], tok::identifier, TT_Unknown);
 
-  Tokens = annotate("int xor = foo;");
+  Tokens = annotate("int xor = foo;", StyleC);
   ASSERT_EQ(Tokens.size(), 6u) << Tokens;
   EXPECT_TOKEN(Tokens[1], tok::identifier, TT_StartOfName);
 }