[PATCH] clang-format: Add option to disable fallback

[Adam Strzelecki]

>From command perspective -no-fallback may be used to indicate that file shall
be not re-formatted if no valid style specified by -style was found.

>From API perspective added in,out Fallback parameter indicating if fallback is
desired and if it was used when resolving style.
---
 include/clang/Format/Format.h      |  4 +++-
 lib/Format/Format.cpp              | 23 ++++++++++++++++-------
 tools/clang-format/ClangFormat.cpp | 22 ++++++++++++++++++----
 3 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/include/clang/Format/Format.h b/include/clang/Format/Format.h
index 09c37d1..034f217 100644
--- a/include/clang/Format/Format.h
+++ b/include/clang/Format/Format.h
@@ -484,11 +484,13 @@ extern const char *StyleOptionHelpDescription;
 /// == "file".
 /// \param[in] FallbackStyle The name of a predefined style used to fallback to
 /// in case the style can't be determined from \p StyleName.
+/// \param[in,out] Fallback indicates if fallback style is intended to be used
+/// and if fallback style was returned.
 ///
 /// \returns FormatStyle as specified by \c StyleName. If no style could be
 /// determined, the default is LLVM Style (see getLLVMStyle()).
 FormatStyle getStyle(StringRef StyleName, StringRef FileName,
-                     StringRef FallbackStyle);
+                     StringRef FallbackStyle, bool &Fallback);
 
 } // end namespace format
 } // end namespace clang
diff --git a/lib/Format/Format.cpp b/lib/Format/Format.cpp
index 60706b1..eef9dfc 100644
--- a/lib/Format/Format.cpp
+++ b/lib/Format/Format.cpp
@@ -1940,18 +1940,20 @@ static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
 }
 
 FormatStyle getStyle(StringRef StyleName, StringRef FileName,
-                     StringRef FallbackStyle) {
+                     StringRef FallbackStyle, bool &Fallback) {
   FormatStyle Style = getLLVMStyle();
   Style.Language = getLanguageByFileName(FileName);
   if (!getPredefinedStyle(FallbackStyle, Style.Language, &Style)) {
     llvm::errs() << "Invalid fallback style \"" << FallbackStyle
                  << "\" using LLVM style\n";
+    Fallback = true;
     return Style;
   }
 
   if (StyleName.startswith("{")) {
     // Parse YAML/JSON style from the command line.
-    if (llvm::error_code ec = parseConfiguration(StyleName, &Style)) {
+    llvm::error_code ec = parseConfiguration(StyleName, &Style);
+    if ((Fallback = !!ec)) {
       llvm::errs() << "Error parsing -style: " << ec.message() << ", using "
                    << FallbackStyle << " style\n";
     }
@@ -1959,9 +1961,10 @@ FormatStyle getStyle(StringRef StyleName, StringRef FileName,
   }
 
   if (!StyleName.equals_lower("file")) {
-    if (!getPredefinedStyle(StyleName, Style.Language, &Style))
+    if ((Fallback = !getPredefinedStyle(StyleName, Style.Language, &Style))) {
       llvm::errs() << "Invalid value for -style, using " << FallbackStyle
                    << " style\n";
+    }
     return Style;
   }
 
@@ -2004,16 +2007,22 @@ FormatStyle getStyle(StringRef StyleName, StringRef FileName,
           UnsuitableConfigFiles.append(ConfigFile);
           continue;
         }
-        llvm::errs() << "Error reading " << ConfigFile << ": " << ec.message()
-                     << "\n";
+        if (Fallback) {
+          llvm::errs() << "Error reading " << ConfigFile << ": " << ec.message()
+                       << "\n";
+        }
         break;
       }
       DEBUG(llvm::dbgs() << "Using configuration file " << ConfigFile << "\n");
+      Fallback = false;
       return Style;
     }
   }
-  llvm::errs() << "Can't find usable .clang-format, using " << FallbackStyle
-               << " style\n";
+  if (Fallback) {
+    llvm::errs() << "Can't find usable .clang-format, using " << FallbackStyle
+                 << " style\n";
+  }
+  Fallback = true;
   if (!UnsuitableConfigFiles.empty()) {
     llvm::errs() << "Configuration file(s) do(es) not support "
                  << getLanguageName(Style.Language) << ": "
diff --git a/tools/clang-format/ClangFormat.cpp b/tools/clang-format/ClangFormat.cpp
index d26659d..6448cfc 100644
--- a/tools/clang-format/ClangFormat.cpp
+++ b/tools/clang-format/ClangFormat.cpp
@@ -71,6 +71,14 @@ FallbackStyle("fallback-style",
                        "file to use."),
               cl::init("LLVM"), cl::cat(ClangFormatCategory));
 
+static cl::opt<bool>
+NoFallback("no-fallback",
+           cl::desc("Skip formatting when style specified with -style\n"
+                    "is not found or is invalid. Empty .clang-format\n"
+                    "file in conjunction with -style=file effectively\n"
+                    "disables formatting inside specific folder."),
+           cl::cat(ClangFormatCategory));
+
 static cl::opt<std::string>
 AssumeFilename("assume-filename",
                cl::desc("When reading from stdin, clang-format assumes this\n"
@@ -220,11 +228,16 @@ static bool format(StringRef FileName) {
   if (fillRanges(Sources, ID, Code.get(), Ranges))
     return true;
 
-  FormatStyle FormatStyle = getStyle(
-      Style, (FileName == "-") ? AssumeFilename : FileName, FallbackStyle);
+  bool Fallback = !NoFallback;
+  FormatStyle FormatStyle =
+      getStyle(Style, (FileName == "-") ? AssumeFilename : FileName,
+               FallbackStyle, Fallback);
   Lexer Lex(ID, Sources.getBuffer(ID), Sources,
             getFormattingLangOpts(FormatStyle.Standard));
-  tooling::Replacements Replaces = reformat(FormatStyle, Lex, Sources, Ranges);
+  tooling::Replacements Replaces;
+  if (!Fallback || !NoFallback) {
+    Replaces = reformat(FormatStyle, Lex, Sources, Ranges);
+  }
   if (OutputXML) {
     llvm::outs()
         << "<?xml version='1.0'?>\n<replacements xml:space='preserve'>\n";
@@ -289,10 +302,11 @@ int main(int argc, const char **argv) {
     cl::PrintHelpMessage();
 
   if (DumpConfig) {
+    bool Fallback = !NoFallback;
     std::string Config =
         clang::format::configurationAsText(clang::format::getStyle(
             Style, FileNames.empty() ? AssumeFilename : FileNames[0],
-            FallbackStyle));
+            FallbackStyle, Fallback));
     llvm::outs() << Config << "\n";
     return 0;
   }
-- 
1.8.5.2 (Apple Git-48)