[clang-format] Add basic support for formatting C# files

Summary:

This revision adds basic support for formatting C# files with clang-format, I know the barrier to entry is high here  so I'm sending this revision in to test the water as to whether this might be something we'd consider landing.

Tracking in Bugzilla as:
https://bugs.llvm.org/show_bug.cgi?id=40850

Justification:
C# code just looks ugly in comparison to the C++ code in our source tree which is clang-formatted.

I've struggled with Visual Studio reformatting to get a clean and consistent style, I want to format our C# code on saving like I do now for C++ and i want it to have the same style as defined in our .clang-format file, so it consistent as it can be with C++.  (Braces/Breaking/Spaces/Indent etc..)

Using clang format without this patch leaves the code in a bad state, sometimes when the BreakStringLiterals is set, it  fails to compile.

Mostly the C# is similar to Java, except instead of JavaAnnotations I try to reuse the TT_AttributeSquare.

Almost the most valuable portion is to have a new Language in order to partition the configuration for C# within a common .clang-format file, with the auto detection on the .cs extension. But there are other C# specific styles that could be added later if this is accepted. in particular how  `{ set;get }` is formatted.

Reviewers: djasper, klimek, krasimir, benhamilton, JonasToth

Reviewed By: klimek

Subscribers: llvm-commits, mgorny, jdoerfert, cfe-commits

Tags: #clang, #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D58404

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356662 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ClangFormat.rst

@@ -11,12 +11,12 @@ Standalone Tool
 ===============
 
 :program:`clang-format` is located in `clang/tools/clang-format` and can be used
-to format C/C++/Java/JavaScript/Objective-C/Protobuf code.
+to format C/C++/Java/JavaScript/Objective-C/Protobuf/C# code.
 
 .. code-block:: console
 
   $ clang-format -help
-  OVERVIEW: A tool to format C/C++/Java/JavaScript/Objective-C/Protobuf code.
+  OVERVIEW: A tool to format C/C++/Java/JavaScript/Objective-C/Protobuf/C# code.
 
   If no arguments are specified, it formats the code from standard input
   and writes the result to the standard output.

docs/ClangFormatStyleOptions.rst

@@ -7,8 +7,8 @@ supported by :doc:`LibFormat` and :doc:`ClangFormat`.
 
 When using :program:`clang-format` command line utility or
 ``clang::format::reformat(...)`` functions from code, one can either use one of
-the predefined styles (LLVM, Google, Chromium, Mozilla, WebKit) or create a
-custom style by configuring specific style options.
+the predefined styles (LLVM, Google, Chromium, Mozilla, WebKit, Microsoft) or
+create a custom style by configuring specific style options.
 
 
 Configuring Style with clang-format
@@ -68,6 +68,10 @@ An example of a configuration file for multiple languages:
   Language: Proto
   # Don't format .proto files.
   DisableFormat: true
+  ---
+  Language: CSharp
+  # Use 100 columns for C#.
+  ColumnLimit: 100
   ...
 
 An easy way to get a valid ``.clang-format`` file containing all configuration
@@ -144,6 +148,9 @@ the configuration (without a prefix: ``Auto``).
   * ``WebKit``
     A style complying with `WebKit's style guide
     <https://www.webkit.org/coding/coding-style.html>`_
+  * ``Microsoft``
+    A style complying with `Microsoft's style guide
+    <https://docs.microsoft.com/en-us/visualstudio/ide/editorconfig-code-style-settings-reference?view=vs-2017>`_
 
 .. START_FORMAT_STYLE_OPTIONS
 
@@ -1552,6 +1559,9 @@ the configuration (without a prefix: ``Auto``).
   * ``LK_Cpp`` (in configuration: ``Cpp``)
     Should be used for C, C++.
 
+  * ``LK_CSharp`` (in configuration: ``CSharp``)
+    Should be used for C#.
+
   * ``LK_Java`` (in configuration: ``Java``)
     Should be used for Java.
 

docs/ReleaseNotes.rst

@@ -165,7 +165,8 @@ release of Clang. Users of the build system should adjust accordingly.
 AST Matchers
 ------------
 
-- ...
+- Add language support for clang-formatting C# files
+- Add Microsoft coding style to encapsulate default C# formatting style
 
 clang-format
 ------------

include/clang/Format/Format.h

@@ -1258,6 +1258,8 @@ struct FormatStyle {
     LK_None,
     /// Should be used for C, C++.
     LK_Cpp,
+    /// Should be used for C#.
+    LK_CSharp,
     /// Should be used for Java.
     LK_Java,
     /// Should be used for JavaScript.
@@ -1274,6 +1276,7 @@ struct FormatStyle {
     LK_TextProto
   };
   bool isCpp() const { return Language == LK_Cpp || Language == LK_ObjC; }
+  bool isCSharp() const { return Language == LK_CSharp; }
 
   /// Language, this format style is targeted at.
   LanguageKind Language;
@@ -2090,6 +2093,8 @@ inline StringRef getLanguageName(FormatStyle::LanguageKind Language) {
   switch (Language) {
   case FormatStyle::LK_Cpp:
     return "C++";
+  case FormatStyle::LK_CSharp:
+    return "CSharp";
   case FormatStyle::LK_ObjC:
     return "Objective-C";
   case FormatStyle::LK_Java:

lib/Format/ContinuationIndenter.cpp

@@ -418,7 +418,8 @@ bool ContinuationIndenter::mustBreak(const LineState &State) {
   if (Style.AlwaysBreakBeforeMultilineStrings &&
       (NewLineColumn == State.FirstIndent + Style.ContinuationIndentWidth ||
        Previous.is(tok::comma) || Current.NestingLevel < 2) &&
-      !Previous.isOneOf(tok::kw_return, tok::lessless, tok::at) &&
+      !Previous.isOneOf(tok::kw_return, tok::lessless, tok::at,
+                        Keywords.kw_dollar) &&
       !Previous.isOneOf(TT_InlineASMColon, TT_ConditionalExpr) &&
       nextIsMultilineString(State))
     return true;
@@ -1158,6 +1159,8 @@ unsigned ContinuationIndenter::moveStateToNextToken(LineState &State,
 
   if (Current.is(TT_ObjCStringLiteral) && State.StartOfStringLiteral == 0)
     State.StartOfStringLiteral = State.Column + 1;
+  if (Current.is(TT_CSharpStringLiteral) && State.StartOfStringLiteral == 0)
+    State.StartOfStringLiteral = State.Column + 1;
   else if (Current.isStringLiteral() && State.StartOfStringLiteral == 0)
     State.StartOfStringLiteral = State.Column;
   else if (!Current.isOneOf(tok::comment, tok::identifier, tok::hash) &&
@@ -1711,10 +1714,11 @@ ContinuationIndenter::createBreakableToken(const FormatToken &Current,
                                            LineState &State, bool AllowBreak) {
   unsigned StartColumn = State.Column - Current.ColumnWidth;
   if (Current.isStringLiteral()) {
-    // FIXME: String literal breaking is currently disabled for Java and JS, as
-    // it requires strings to be merged using "+" which we don't support.
+    // FIXME: String literal breaking is currently disabled for C#,Java and
+    // JavaScript, as it requires strings to be merged using "+" which we
+    // don't support.
     if (Style.Language == FormatStyle::LK_Java ||
-        Style.Language == FormatStyle::LK_JavaScript ||
+        Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp() ||
         !Style.BreakStringLiterals || !AllowBreak)
       return nullptr;
 

lib/Format/Format.cpp

@@ -61,6 +61,7 @@ template <> struct ScalarEnumerationTraits<FormatStyle::LanguageKind> {
     IO.enumCase(Value, "Proto", FormatStyle::LK_Proto);
     IO.enumCase(Value, "TableGen", FormatStyle::LK_TableGen);
     IO.enumCase(Value, "TextProto", FormatStyle::LK_TextProto);
+    IO.enumCase(Value, "CSharp", FormatStyle::LK_CSharp);
   }
 };
 
@@ -287,8 +288,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("Language", Style.Language);
 
     if (IO.outputting()) {
-      StringRef StylesArray[] = {"LLVM",    "Google", "Chromium",
-                                 "Mozilla", "WebKit", "GNU"};
+      StringRef StylesArray[] = {"LLVM",   "Google", "Chromium", "Mozilla",
+                                 "WebKit", "GNU",    "Microsoft"};
       ArrayRef<StringRef> Styles(StylesArray);
       for (size_t i = 0, e = Styles.size(); i < e; ++i) {
         StringRef StyleName(Styles[i]);
@@ -951,6 +952,32 @@ FormatStyle getGNUStyle() {
   return Style;
 }
 
+FormatStyle getMicrosoftStyle(FormatStyle::LanguageKind Language) {
+  FormatStyle Style = getLLVMStyle();
+  Style.ColumnLimit = 120;
+  Style.TabWidth = 4;
+  Style.IndentWidth = 4;
+  Style.UseTab = FormatStyle::UT_Never;
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterClass = true;
+  Style.BraceWrapping.AfterControlStatement = true;
+  Style.BraceWrapping.AfterEnum = true;
+  Style.BraceWrapping.AfterFunction = true;
+  Style.BraceWrapping.AfterNamespace = true;
+  Style.BraceWrapping.AfterObjCDeclaration = true;
+  Style.BraceWrapping.AfterStruct = true;
+  Style.BraceWrapping.AfterExternBlock = true;
+  Style.BraceWrapping.BeforeCatch = true;
+  Style.BraceWrapping.BeforeElse = true;
+  Style.PenaltyReturnTypeOnItsOwnLine = 1000;
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
+  Style.AllowShortBlocksOnASingleLine = false;
+  Style.AllowShortCaseLabelsOnASingleLine = false;
+  Style.AllowShortIfStatementsOnASingleLine = FormatStyle::SIS_Never;
+  Style.AllowShortLoopsOnASingleLine = false;
+  return Style;
+}
+
 FormatStyle getNoStyle() {
   FormatStyle NoStyle = getLLVMStyle();
   NoStyle.DisableFormat = true;
@@ -973,6 +1000,8 @@ bool getPredefinedStyle(StringRef Name, FormatStyle::LanguageKind Language,
     *Style = getWebKitStyle();
   } else if (Name.equals_lower("gnu")) {
     *Style = getGNUStyle();
+  } else if (Name.equals_lower("microsoft")) {
+    *Style = getMicrosoftStyle(Language);
   } else if (Name.equals_lower("none")) {
     *Style = getNoStyle();
   } else {
@@ -2323,6 +2352,8 @@ static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
     return FormatStyle::LK_TextProto;
   if (FileName.endswith_lower(".td"))
     return FormatStyle::LK_TableGen;
+  if (FileName.endswith_lower(".cs"))
+    return FormatStyle::LK_CSharp;
   return FormatStyle::LK_Cpp;
 }
 

lib/Format/FormatToken.h

@@ -96,6 +96,8 @@ namespace format {
   TYPE(TrailingReturnArrow)                                                    \
   TYPE(TrailingUnaryOperator)                                                  \
   TYPE(UnaryOperator)                                                          \
+  TYPE(CSharpStringLiteral)                                                    \
+  TYPE(CSharpNullCoalescing)                                                   \
   TYPE(Unknown)
 
 enum TokenType {
@@ -723,7 +725,36 @@ struct AdditionalKeywords {
     kw_slots = &IdentTable.get("slots");
     kw_qslots = &IdentTable.get("Q_SLOTS");
 
-    // Keep this at the end of the constructor to make sure everything here is
+    // C# keywords
+    kw_dollar = &IdentTable.get("dollar");
+    kw_base = &IdentTable.get("base");
+    kw_byte = &IdentTable.get("byte");
+    kw_checked = &IdentTable.get("checked");
+    kw_decimal = &IdentTable.get("decimal");
+    kw_delegate = &IdentTable.get("delegate");
+    kw_event = &IdentTable.get("event");
+    kw_fixed = &IdentTable.get("fixed");
+    kw_foreach = &IdentTable.get("foreach");
+    kw_implicit = &IdentTable.get("implicit");
+    kw_internal = &IdentTable.get("internal");
+    kw_lock = &IdentTable.get("lock");
+    kw_null = &IdentTable.get("null");
+    kw_object = &IdentTable.get("object");
+    kw_out = &IdentTable.get("out");
+    kw_params = &IdentTable.get("params");
+    kw_ref = &IdentTable.get("ref");
+    kw_string = &IdentTable.get("string");
+    kw_stackalloc = &IdentTable.get("stackalloc");
+    kw_sbyte = &IdentTable.get("sbyte");
+    kw_sealed = &IdentTable.get("sealed");
+    kw_uint = &IdentTable.get("uint");
+    kw_ulong = &IdentTable.get("ulong");
+    kw_unchecked = &IdentTable.get("unchecked");
+    kw_unsafe = &IdentTable.get("unsafe");
+    kw_ushort = &IdentTable.get("ushort");
+
+    // Keep this at the end of the constructor to make sure everything here
+    // is
     // already initialized.
     JsExtraKeywords = std::unordered_set<IdentifierInfo *>(
         {kw_as, kw_async, kw_await, kw_declare, kw_finally, kw_from,
@@ -731,6 +762,19 @@ struct AdditionalKeywords {
          kw_set, kw_type, kw_typeof, kw_var, kw_yield,
          // Keywords from the Java section.
          kw_abstract, kw_extends, kw_implements, kw_instanceof, kw_interface});
+
+    CSharpExtraKeywords = std::unordered_set<IdentifierInfo *>(
+        {kw_base, kw_byte, kw_checked, kw_decimal, kw_delegate, kw_event,
+         kw_fixed, kw_foreach, kw_implicit, kw_in, kw_interface, kw_internal,
+         kw_is, kw_lock, kw_null, kw_object, kw_out, kw_override, kw_params,
+         kw_readonly, kw_ref, kw_string, kw_stackalloc, kw_sbyte, kw_sealed,
+         kw_uint, kw_ulong, kw_unchecked, kw_unsafe, kw_ushort,
+         // Keywords from the JavaScript section.
+         kw_as, kw_async, kw_await, kw_declare, kw_finally, kw_from,
+         kw_function, kw_get, kw_import, kw_is, kw_let, kw_module, kw_readonly,
+         kw_set, kw_type, kw_typeof, kw_var, kw_yield,
+         // Keywords from the Java section.
+         kw_abstract, kw_extends, kw_implements, kw_instanceof, kw_interface});
   }
 
   // Context sensitive keywords.
@@ -796,6 +840,37 @@ struct AdditionalKeywords {
   IdentifierInfo *kw_slots;
   IdentifierInfo *kw_qslots;
 
+  // C# keywords
+  IdentifierInfo *kw_dollar;
+  IdentifierInfo *kw_base;
+  IdentifierInfo *kw_byte;
+  IdentifierInfo *kw_checked;
+  IdentifierInfo *kw_decimal;
+  IdentifierInfo *kw_delegate;
+  IdentifierInfo *kw_event;
+  IdentifierInfo *kw_fixed;
+  IdentifierInfo *kw_foreach;
+  IdentifierInfo *kw_implicit;
+  IdentifierInfo *kw_internal;
+
+  IdentifierInfo *kw_lock;
+  IdentifierInfo *kw_null;
+  IdentifierInfo *kw_object;
+  IdentifierInfo *kw_out;
+
+  IdentifierInfo *kw_params;
+
+  IdentifierInfo *kw_ref;
+  IdentifierInfo *kw_string;
+  IdentifierInfo *kw_stackalloc;
+  IdentifierInfo *kw_sbyte;
+  IdentifierInfo *kw_sealed;
+  IdentifierInfo *kw_uint;
+  IdentifierInfo *kw_ulong;
+  IdentifierInfo *kw_unchecked;
+  IdentifierInfo *kw_unsafe;
+  IdentifierInfo *kw_ushort;
+
   /// Returns \c true if \p Tok is a true JavaScript identifier, returns
   /// \c false if it is a keyword or a pseudo keyword.
   bool IsJavaScriptIdentifier(const FormatToken &Tok) const {
@@ -804,9 +879,68 @@ struct AdditionalKeywords {
                JsExtraKeywords.end();
   }
 
+  /// Returns \c true if \p Tok is a C# keyword, returns
+  /// \c false if it is a anything else.
+  bool isCSharpKeyword(const FormatToken &Tok) const {
+    switch (Tok.Tok.getKind()) {
+    case tok::kw_bool:
+    case tok::kw_break:
+    case tok::kw_case:
+    case tok::kw_catch:
+    case tok::kw_char:
+    case tok::kw_class:
+    case tok::kw_const:
+    case tok::kw_continue:
+    case tok::kw_default:
+    case tok::kw_do:
+    case tok::kw_double:
+    case tok::kw_else:
+    case tok::kw_enum:
+    case tok::kw_explicit:
+    case tok::kw_extern:
+    case tok::kw_false:
+    case tok::kw_float:
+    case tok::kw_for:
+    case tok::kw_goto:
+    case tok::kw_if:
+    case tok::kw_int:
+    case tok::kw_long:
+    case tok::kw_namespace:
+    case tok::kw_new:
+    case tok::kw_operator:
+    case tok::kw_private:
+    case tok::kw_protected:
+    case tok::kw_public:
+    case tok::kw_return:
+    case tok::kw_short:
+    case tok::kw_sizeof:
+    case tok::kw_static:
+    case tok::kw_struct:
+    case tok::kw_switch:
+    case tok::kw_this:
+    case tok::kw_throw:
+    case tok::kw_true:
+    case tok::kw_try:
+    case tok::kw_typeof:
+    case tok::kw_using:
+    case tok::kw_virtual:
+    case tok::kw_void:
+    case tok::kw_volatile:
+    case tok::kw_while:
+      return true;
+    default:
+      return Tok.is(tok::identifier) &&
+             CSharpExtraKeywords.find(Tok.Tok.getIdentifierInfo()) ==
+                 CSharpExtraKeywords.end();
+    }
+  }
+
 private:
   /// The JavaScript keywords beyond the C++ keyword set.
   std::unordered_set<IdentifierInfo *> JsExtraKeywords;
+
+  /// The C# keywords beyond the C++ keyword set
+  std::unordered_set<IdentifierInfo *> CSharpExtraKeywords;
 };
 
 } // namespace format

lib/Format/FormatTokenLexer.cpp

@@ -66,6 +66,21 @@ void FormatTokenLexer::tryMergePreviousTokens() {
     return;
   if (tryMergeLessLess())
     return;
+
+  if (Style.isCSharp()) {
+    if (tryMergeCSharpKeywordVariables())
+      return;
+    if (tryMergeCSharpVerbatimStringLiteral())
+      return;
+    if (tryMergeCSharpDoubleQuestion())
+      return;
+    if (tryMergeCSharpNullConditionals())
+      return;
+    static const tok::TokenKind JSRightArrow[] = {tok::equal, tok::greater};
+    if (tryMergeTokens(JSRightArrow, TT_JsFatArrow))
+      return;
+  }
+
   if (tryMergeNSStringLiteral())
     return;
 
@@ -142,6 +157,100 @@ bool FormatTokenLexer::tryMergeJSPrivateIdentifier() {
   return true;
 }
 
+// Search for verbatim or interpolated string literals @"ABC" or
+// $"aaaaa{abc}aaaaa" i and mark the token as TT_CSharpStringLiteral, and to
+// prevent splitting of @, $ and ".
+bool FormatTokenLexer::tryMergeCSharpVerbatimStringLiteral() {
+  if (Tokens.size() < 2)
+    return false;
+  auto &At = *(Tokens.end() - 2);
+  auto &String = *(Tokens.end() - 1);
+
+  // Look for $"aaaaaa" @"aaaaaa".
+  if (!(At->is(tok::at) || At->TokenText == "$") ||
+      !String->is(tok::string_literal))
+    return false;
+
+  if (Tokens.size() >= 2 && At->is(tok::at)) {
+    auto &Dollar = *(Tokens.end() - 3);
+    if (Dollar->TokenText == "$") {
+      // This looks like $@"aaaaa" so we need to combine all 3 tokens.
+      Dollar->Tok.setKind(tok::string_literal);
+      Dollar->TokenText =
+          StringRef(Dollar->TokenText.begin(),
+                    String->TokenText.end() - Dollar->TokenText.begin());
+      Dollar->ColumnWidth += (At->ColumnWidth + String->ColumnWidth);
+      Dollar->Type = TT_CSharpStringLiteral;
+      Tokens.erase(Tokens.end() - 2);
+      Tokens.erase(Tokens.end() - 1);
+      return true;
+    }
+  }
+
+  // Convert back into just a string_literal.
+  At->Tok.setKind(tok::string_literal);
+  At->TokenText = StringRef(At->TokenText.begin(),
+                            String->TokenText.end() - At->TokenText.begin());
+  At->ColumnWidth += String->ColumnWidth;
+  At->Type = TT_CSharpStringLiteral;
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
+bool FormatTokenLexer::tryMergeCSharpDoubleQuestion() {
+  if (Tokens.size() < 2)
+    return false;
+  auto &FirstQuestion = *(Tokens.end() - 2);
+  auto &SecondQuestion = *(Tokens.end() - 1);
+  if (!FirstQuestion->is(tok::question) || !SecondQuestion->is(tok::question))
+    return false;
+  FirstQuestion->Tok.setKind(tok::question);
+  FirstQuestion->TokenText = StringRef(FirstQuestion->TokenText.begin(),
+                                       SecondQuestion->TokenText.end() -
+                                           FirstQuestion->TokenText.begin());
+  FirstQuestion->ColumnWidth += SecondQuestion->ColumnWidth;
+  FirstQuestion->Type = TT_CSharpNullCoalescing;
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
+bool FormatTokenLexer::tryMergeCSharpKeywordVariables() {
+  if (Tokens.size() < 2)
+    return false;
+  auto &At = *(Tokens.end() - 2);
+  auto &Keyword = *(Tokens.end() - 1);
+  if (!At->is(tok::at))
+    return false;
+  if (!Keywords.isCSharpKeyword(*Keyword))
+    return false;
+
+  At->Tok.setKind(tok::identifier);
+  At->TokenText = StringRef(At->TokenText.begin(),
+                            Keyword->TokenText.end() - At->TokenText.begin());
+  At->ColumnWidth += Keyword->ColumnWidth;
+  At->Type = Keyword->Type;
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
+// In C# merge the Identifier and the ? together e.g. arg?.
+bool FormatTokenLexer::tryMergeCSharpNullConditionals() {
+  if (Tokens.size() < 2)
+    return false;
+  auto &Identifier = *(Tokens.end() - 2);
+  auto &Question = *(Tokens.end() - 1);
+  if (!Identifier->isOneOf(tok::r_square, tok::identifier) ||
+      !Question->is(tok::question))
+    return false;
+  Identifier->TokenText =
+      StringRef(Identifier->TokenText.begin(),
+                Question->TokenText.end() - Identifier->TokenText.begin());
+  Identifier->ColumnWidth += Question->ColumnWidth;
+  Identifier->Type = Identifier->Type;
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
 bool FormatTokenLexer::tryMergeLessLess() {
   // Merge X,less,less,Y into X,lessless,Y unless X or Y is less.
   if (Tokens.size() < 3)

lib/Format/FormatTokenLexer.h

@@ -49,6 +49,10 @@ private:
   bool tryMergeLessLess();
   bool tryMergeNSStringLiteral();
   bool tryMergeJSPrivateIdentifier();
+  bool tryMergeCSharpVerbatimStringLiteral();
+  bool tryMergeCSharpKeywordVariables();
+  bool tryMergeCSharpNullConditionals();
+  bool tryMergeCSharpDoubleQuestion();
 
   bool tryMergeTokens(ArrayRef<tok::TokenKind> Kinds, TokenType NewType);
 

lib/Format/TokenAnnotator.cpp

@@ -298,6 +298,8 @@ private:
           CurrentToken->Type = TT_JavaAnnotation;
         if (Left->Previous && Left->Previous->is(TT_LeadingJavaAnnotation))
           CurrentToken->Type = TT_LeadingJavaAnnotation;
+        if (Left->Previous && Left->Previous->is(TT_AttributeSquare))
+          CurrentToken->Type = TT_AttributeSquare;
 
         if (!HasMultipleLines)
           Left->PackingKind = PPK_Inconclusive;
@@ -348,6 +350,40 @@ private:
     return false;
   }
 
+  bool isCSharpAttributeSpecifier(const FormatToken &Tok) {
+    if (!Style.isCSharp())
+      return false;
+
+    const FormatToken *AttrTok = Tok.Next;
+    if (!AttrTok)
+      return false;
+
+    // Just an empty declaration e.g. string [].
+    if (AttrTok->is(tok::r_square))
+      return false;
+
+    // Move along the tokens inbetween the '[' and ']' e.g. [STAThread].
+    while (AttrTok && AttrTok->isNot(tok::r_square)) {
+      AttrTok = AttrTok->Next;
+    }
+
+    if (!AttrTok)
+      return false;
+
+    // Move past the end of ']'.
+    AttrTok = AttrTok->Next;
+    if (!AttrTok)
+      return false;
+
+    // Limit this to being an access modifier that follows.
+    if (AttrTok->isOneOf(tok::kw_public, tok::kw_private, tok::kw_protected,
+                         tok::kw_class, tok::kw_static, tok::l_square,
+                         Keywords.kw_internal)) {
+      return true;
+    }
+    return false;
+  }
+
   bool isCpp11AttributeSpecifier(const FormatToken &Tok) {
     if (!Style.isCpp() || !Tok.startsSequence(tok::l_square, tok::l_square))
       return false;
@@ -398,6 +434,11 @@ private:
     bool IsCpp11AttributeSpecifier = isCpp11AttributeSpecifier(*Left) ||
                                      Contexts.back().InCpp11AttributeSpecifier;
 
+    // Treat C# Attributes [STAThread] much like C++ attributes [[...]].
+    bool IsCSharp11AttributeSpecifier =
+        isCSharpAttributeSpecifier(*Left) ||
+        Contexts.back().InCSharpAttributeSpecifier;
+
     bool InsideInlineASM = Line.startsWith(tok::kw_asm);
     bool StartsObjCMethodExpr =
         !InsideInlineASM && !CppArrayTemplates && Style.isCpp() &&
@@ -478,6 +519,8 @@ private:
                                  // Should only be relevant to JavaScript:
                                  tok::kw_default)) {
         Left->Type = TT_ArrayInitializerLSquare;
+      } else if (IsCSharp11AttributeSpecifier) {
+        Left->Type = TT_AttributeSquare;
       } else {
         BindingIncrease = 10;
         Left->Type = TT_ArraySubscriptLSquare;
@@ -492,11 +535,14 @@ private:
 
     Contexts.back().ColonIsObjCMethodExpr = StartsObjCMethodExpr;
     Contexts.back().InCpp11AttributeSpecifier = IsCpp11AttributeSpecifier;
+    Contexts.back().InCSharpAttributeSpecifier = IsCSharp11AttributeSpecifier;
 
     while (CurrentToken) {
       if (CurrentToken->is(tok::r_square)) {
         if (IsCpp11AttributeSpecifier)
           CurrentToken->Type = TT_AttributeSquare;
+        if (IsCSharp11AttributeSpecifier)
+          CurrentToken->Type = TT_AttributeSquare;
         else if (((CurrentToken->Next &&
                    CurrentToken->Next->is(tok::l_paren)) ||
                   (CurrentToken->Previous &&
@@ -1193,6 +1239,7 @@ private:
     bool CaretFound = false;
     bool IsForEachMacro = false;
     bool InCpp11AttributeSpecifier = false;
+    bool InCSharpAttributeSpecifier = false;
   };
 
   /// Puts a new \c Context onto the stack \c Contexts for the lifetime
@@ -2630,7 +2677,7 @@ bool TokenAnnotator::spaceRequiredBefore(const AnnotatedLine &Line,
     // and "%d %d"
     if (Left.is(tok::numeric_constant) && Right.is(tok::percent))
       return Right.WhitespaceRange.getEnd() != Right.WhitespaceRange.getBegin();
-  } else if (Style.Language == FormatStyle::LK_JavaScript) {
+  } else if (Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp()) {
     if (Left.is(TT_JsFatArrow))
       return true;
     // for await ( ...
@@ -2977,6 +3024,14 @@ bool TokenAnnotator::mustBreakBefore(const AnnotatedLine &Line,
   if (Left.is(TT_ObjCBlockLBrace) && !Style.AllowShortBlocksOnASingleLine)
     return true;
 
+  // Put multiple C# attributes on a new line.
+  if (Style.isCSharp() &&
+      ((Left.is(TT_AttributeSquare) && Left.is(tok::r_square)) ||
+       (Left.is(tok::r_square) && Right.is(TT_AttributeSquare) &&
+        Right.is(tok::l_square))))
+    return true;
+
+  // Put multiple Java annotation on a new line.
   if ((Style.Language == FormatStyle::LK_Java ||
        Style.Language == FormatStyle::LK_JavaScript) &&
       Left.is(TT_LeadingJavaAnnotation) &&

lib/Format/UnwrappedLineFormatter.cpp

@@ -94,7 +94,7 @@ private:
   /// characters to the left from their level.
   int getIndentOffset(const FormatToken &RootToken) {
     if (Style.Language == FormatStyle::LK_Java ||
-        Style.Language == FormatStyle::LK_JavaScript)
+        Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp())
       return 0;
     if (RootToken.isAccessSpecifier(false) ||
         RootToken.isObjCAccessSpecifier() ||
@@ -1073,7 +1073,9 @@ unsigned UnwrappedLineFormatter::format(
           TheLine.Last->TotalLength + Indent <= ColumnLimit ||
           (TheLine.Type == LT_ImportStatement &&
            (Style.Language != FormatStyle::LK_JavaScript ||
-            !Style.JavaScriptWrapImports));
+            !Style.JavaScriptWrapImports)) ||
+          (Style.isCSharp() &&
+           TheLine.InPPDirective); // don't split #regions in C#
       if (Style.ColumnLimit == 0)
         NoColumnLimitLineFormatter(Indenter, Whitespaces, Style, this)
             .formatLine(TheLine, NextStartColumn + Indent,

lib/Format/UnwrappedLineParser.cpp

@@ -1000,7 +1000,7 @@ void UnwrappedLineParser::parseStructuralElement() {
   case tok::kw_protected:
   case tok::kw_private:
     if (Style.Language == FormatStyle::LK_Java ||
-        Style.Language == FormatStyle::LK_JavaScript)
+        Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp())
       nextToken();
     else
       parseAccessSpecifier();
@@ -1214,9 +1214,9 @@ void UnwrappedLineParser::parseStructuralElement() {
       // parseRecord falls through and does not yet add an unwrapped line as a
       // record declaration or definition can start a structural element.
       parseRecord();
-      // This does not apply for Java and JavaScript.
+      // This does not apply for Java, JavaScript and C#.
       if (Style.Language == FormatStyle::LK_Java ||
-          Style.Language == FormatStyle::LK_JavaScript) {
+          Style.Language == FormatStyle::LK_JavaScript || Style.isCSharp()) {
         if (FormatTok->is(tok::semi))
           nextToken();
         addUnwrappedLine();

tools/clang-format/ClangFormat.cpp

@@ -345,7 +345,7 @@ int main(int argc, const char **argv) {
   cl::SetVersionPrinter(PrintVersion);
   cl::ParseCommandLineOptions(
       argc, argv,
-      "A tool to format C/C++/Java/JavaScript/Objective-C/Protobuf code.\n\n"
+      "A tool to format C/C++/Java/JavaScript/Objective-C/Protobuf/C# code.\n\n"
       "If no arguments are specified, it formats the code from standard input\n"
       "and writes the result to the standard output.\n"
       "If <file>s are given, it reformats the files. If -i is specified\n"

unittests/Format/CMakeLists.txt

@@ -6,6 +6,7 @@ add_clang_unittest(FormatTests
   CleanupTest.cpp
   FormatTest.cpp
   FormatTestComments.cpp
+  FormatTestCSharp.cpp
   FormatTestJS.cpp
   FormatTestJava.cpp
   FormatTestObjC.cpp

unittests/Format/FormatTestCSharp.cpp

@@ -0,0 +1,184 @@
+//===- unittest/Format/FormatTestCSharp.cpp - Formatting tests for CSharp -===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "FormatTestUtils.h"
+#include "clang/Format/Format.h"
+#include "llvm/Support/Debug.h"
+#include "gtest/gtest.h"
+
+#define DEBUG_TYPE "format-test"
+
+namespace clang {
+namespace format {
+
+class FormatTestCSharp : public ::testing::Test {
+protected:
+  static std::string format(llvm::StringRef Code, unsigned Offset,
+                            unsigned Length, const FormatStyle &Style) {
+    LLVM_DEBUG(llvm::errs() << "---\n");
+    LLVM_DEBUG(llvm::errs() << Code << "\n\n");
+    std::vector<tooling::Range> Ranges(1, tooling::Range(Offset, Length));
+    tooling::Replacements Replaces = reformat(Style, Code, Ranges);
+    auto Result = applyAllReplacements(Code, Replaces);
+    EXPECT_TRUE(static_cast<bool>(Result));
+    LLVM_DEBUG(llvm::errs() << "\n" << *Result << "\n\n");
+    return *Result;
+  }
+
+  static std::string
+  format(llvm::StringRef Code,
+         const FormatStyle &Style = getGoogleStyle(FormatStyle::LK_CSharp)) {
+    return format(Code, 0, Code.size(), Style);
+  }
+
+  static FormatStyle getStyleWithColumns(unsigned ColumnLimit) {
+    FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+    Style.ColumnLimit = ColumnLimit;
+    return Style;
+  }
+
+  static void verifyFormat(
+      llvm::StringRef Code,
+      const FormatStyle &Style = getGoogleStyle(FormatStyle::LK_CSharp)) {
+    EXPECT_EQ(Code.str(), format(Code, Style)) << "Expected code is not stable";
+    EXPECT_EQ(Code.str(), format(test::messUp(Code), Style));
+  }
+};
+
+TEST_F(FormatTestCSharp, CSharpClass) {
+  verifyFormat("public class SomeClass {\n"
+               "  void f() {}\n"
+               "  int g() { return 0; }\n"
+               "  void h() {\n"
+               "    while (true) f();\n"
+               "    for (;;) f();\n"
+               "    if (true) f();\n"
+               "  }\n"
+               "}");
+}
+
+TEST_F(FormatTestCSharp, AccessModifiers) {
+  verifyFormat("public String toString() {}");
+  verifyFormat("private String toString() {}");
+  verifyFormat("protected String toString() {}");
+  verifyFormat("internal String toString() {}");
+
+  verifyFormat("public override String toString() {}");
+  verifyFormat("private override String toString() {}");
+  verifyFormat("protected override String toString() {}");
+  verifyFormat("internal override String toString() {}");
+
+  verifyFormat("internal static String toString() {}");
+}
+
+TEST_F(FormatTestCSharp, NoStringLiteralBreaks) {
+  verifyFormat("foo("
+               "\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+               "aaaaaa\");");
+}
+
+TEST_F(FormatTestCSharp, CSharpVerbatiumStringLiterals) {
+  verifyFormat("foo(@\"aaaaaaaa\\abc\\aaaa\");");
+  // @"ABC\" + ToString("B") - handle embedded \ in literal string at
+  // the end
+  //
+  /*
+   * After removal of Lexer change we are currently not able
+   * To handle these cases
+   verifyFormat("string s = @\"ABC\\\" + ToString(\"B\");");
+   verifyFormat("string s = @\"ABC\"\"DEF\"\"GHI\"");
+   verifyFormat("string s = @\"ABC\"\"DEF\"\"\"");
+   verifyFormat("string s = @\"ABC\"\"DEF\"\"\" + abc");
+  */
+}
+
+TEST_F(FormatTestCSharp, CSharpInterpolatedStringLiterals) {
+  verifyFormat("foo($\"aaaaaaaa{aaa}aaaa\");");
+  verifyFormat("foo($\"aaaa{A}\");");
+  verifyFormat(
+      "foo($\"aaaa{A}"
+      "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\");");
+  verifyFormat("Name = $\"{firstName} {lastName}\";");
+
+  // $"ABC\" + ToString("B") - handle embedded \ in literal string at
+  // the end
+  verifyFormat("string s = $\"A{abc}BC\" + ToString(\"B\");");
+  verifyFormat("$\"{domain}\\\\{user}\"");
+  verifyFormat(
+      "var verbatimInterpolated = $@\"C:\\Users\\{userName}\\Documents\\\";");
+}
+
+TEST_F(FormatTestCSharp, CSharpFatArrows) {
+  verifyFormat("Task serverTask = Task.Run(async() => {");
+  verifyFormat("public override string ToString() => \"{Name}\\{Age}\";");
+}
+
+TEST_F(FormatTestCSharp, CSharpNullConditional) {
+  verifyFormat(
+      "public Person(string firstName, string lastName, int? age=null)");
+
+  verifyFormat("switch(args?.Length)");
+
+  verifyFormat("public static void Main(string[] args) { string dirPath "
+               "= args?[0]; }");
+}
+
+TEST_F(FormatTestCSharp, Attributes) {
+  verifyFormat("[STAThread]\n"
+               "static void\n"
+               "Main(string[] args) {}");
+
+  verifyFormat("[TestMethod]\n"
+               "private class Test {}");
+
+  verifyFormat("[TestMethod]\n"
+               "protected class Test {}");
+
+  verifyFormat("[TestMethod]\n"
+               "internal class Test {}");
+
+  verifyFormat("[TestMethod]\n"
+               "class Test {}");
+
+  verifyFormat("[TestMethod]\n"
+               "[DeploymentItem(\"Test.txt\")]\n"
+               "public class Test {}");
+
+  verifyFormat("[System.AttributeUsage(System.AttributeTargets.Method)]\n"
+               "[System.Runtime.InteropServices.ComVisible(true)]\n"
+               "public sealed class STAThreadAttribute : Attribute {}");
+
+  verifyFormat("[Verb(\"start\", HelpText = \"Starts the server listening on "
+               "provided port\")]\n"
+               "class Test {}");
+
+  verifyFormat("[TestMethod]\n"
+               "public string Host {\n  set;\n  get;\n}");
+
+  verifyFormat("[TestMethod(\"start\", HelpText = \"Starts the server "
+               "listening on provided host\")]\n"
+               "public string Host {\n  set;\n  get;\n}");
+}
+
+TEST_F(FormatTestCSharp, CSharpRegions) {
+  verifyFormat("#region aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa "
+               "aaaaaaaaaaaaaaa long region");
+}
+
+TEST_F(FormatTestCSharp, CSharpKeyWordEscaping) {
+  verifyFormat("public enum var { none, @string, bool, @enum }");
+}
+
+TEST_F(FormatTestCSharp, CSharpNullCoalescing) {
+  verifyFormat("var test = ABC ?? DEF");
+  verifyFormat("string myname = name ?? \"ABC\";");
+  verifyFormat("return _name ?? \"DEF\";");
+}
+
+} // namespace format
+} // end namespace clang