clang-format: Introduce DisableFormat that prevents formatting.

And "none" pseudo-style indicating that formatting should be not
applied.

(1) Using .clang-format with "DisableFormat: true" effectively prevents
formatting for all files within the folder containing such .clang-format
file.

(2) Using -fallback-style=none together with -style=file prevents
formatting when .clang-format is not found, which can be used in on-save
callback.

Patch by Adam Strzelecki. Thank you!

llvm-svn: 209446

clang/include/clang/Format/Format.h

@@ -322,6 +322,9 @@ struct FormatStyle {
   /// which should not be split into lines or otherwise changed.
   std::string CommentPragmas;
 
+  /// \brief Disables formatting at all.
+  bool DisableFormat;
+
   /// \brief A vector of macros that should be interpreted as foreach loops
   /// instead of as function calls.
   ///
@@ -422,6 +425,9 @@ FormatStyle getWebKitStyle();
 /// http://www.gnu.org/prep/standards/standards.html
 FormatStyle getGNUStyle();
 
+/// \brief Returns style indicating formatting should be not applied at all.
+FormatStyle getNoStyle();
+
 /// \brief Gets a predefined style for the specified language by name.
 ///
 /// Currently supported names: LLVM, Google, Chromium, Mozilla. Names are

clang/lib/Format/Format.cpp

@@ -223,6 +223,7 @@ template <> struct MappingTraits<FormatStyle> {
                      Style.SpaceBeforeParens);
     }
     IO.mapOptional("SpaceBeforeParens", Style.SpaceBeforeParens);
+    IO.mapOptional("DisableFormat", Style.DisableFormat);
   }
 };
 
@@ -314,6 +315,8 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.PenaltyReturnTypeOnItsOwnLine = 60;
   LLVMStyle.PenaltyBreakBeforeFirstCallParameter = 19;
 
+  LLVMStyle.DisableFormat = false;
+
   return LLVMStyle;
 }
 
@@ -409,6 +412,12 @@ FormatStyle getGNUStyle() {
   return Style;
 }
 
+FormatStyle getNoStyle() {
+  FormatStyle NoStyle = getLLVMStyle();
+  NoStyle.DisableFormat = true;
+  return NoStyle;
+}
+
 bool getPredefinedStyle(StringRef Name, FormatStyle::LanguageKind Language,
                         FormatStyle *Style) {
   if (Name.equals_lower("llvm")) {
@@ -423,6 +432,8 @@ bool getPredefinedStyle(StringRef Name, FormatStyle::LanguageKind Language,
     *Style = getWebKitStyle();
   } else if (Name.equals_lower("gnu")) {
     *Style = getGNUStyle();
+  } else if (Name.equals_lower("none")) {
+    *Style = getNoStyle();
   } else {
     return false;
   }
@@ -1909,6 +1920,11 @@ private:
 tooling::Replacements reformat(const FormatStyle &Style, Lexer &Lex,
                                SourceManager &SourceMgr,
                                std::vector<CharSourceRange> Ranges) {
+  if (Style.DisableFormat) {
+    tooling::Replacements EmptyResult;
+    return EmptyResult;
+  }
+
   Formatter formatter(Style, Lex, SourceMgr, Ranges);
   return formatter.format();
 }

clang/tools/clang-format/ClangFormat.cpp

@@ -68,7 +68,8 @@ FallbackStyle("fallback-style",
               cl::desc("The name of the predefined style used as a\n"
                        "fallback in case clang-format is invoked with\n"
                        "-style=file, but can not find the .clang-format\n"
-                       "file to use."),
+                       "file to use.\n"
+                       "Use -fallback-style=none to skip formatting."),
               cl::init("LLVM"), cl::cat(ClangFormatCategory));
 
 static cl::opt<std::string>