Add arbitrary file/path support to clang-format style file selection

[dciliske]

Summary

The Format library has no way to specify a specific file to be used as the style source. It climbs the path looking for ‘.clang_format’. This patch adds the ability to specify a specific file to use for clang Format utilities.

This patch is in direct response to https://bugs.llvm.org//show_bug.cgi?id=28107 (along with my own personal need).

New style argument feature:

Use -style=file,<filename> to load style
configuration from an explicitly defined file.

[ioeric]

Hi Dan, thanks for the patch! D33560, which adds the same feature, is already under review :)

[dciliske]

So... how should I get something added? That patch has been sitting for a couple weeks.

Should I work on that patch? If so, how do I work on it? This is the first time I'm working on a large OSS project.

[MyDeveloperDay]

I recently hit this issue where I was clang-formatting generated code out of a source tree, which was then copied into a source tree. This failed my post build clang-format validation check and I couldn't understand why. it was only later I realised that unless I have the same .clang-format file locally when I clang-format the generated files or if I only clang-format them after I've copied them in will this work.

A patch like this (and this isn't the only one I've seen like this that lets me point clang-format to a specifc .clang-format file would have helped here.) are you interested in this patch or something like this still? (I realize its a long time since you got a response)

[MyDeveloperDay]

I think we can abandon this revision now we support --style=file:<filename>

lib/Format/Format.cpp

 
 const char *StyleOptionHelpDescription =
     "Coding style, currently supports:\n"
     "  LLVM, Google, Chromium, Mozilla, WebKit.\n"
     "Use -style=file to load style configuration from\n"
     ".clang-format file located in one of the parent\n"
     "directories of the source file (or current\n"
     "directory for stdin).\n"
+    "Use -style=file,<filename> to load style \n"
+    "configuration from an explicitly defined file.\n"
     "Use -style=\"{key: value, ...}\" to set specific\n"
     "parameters, e.g.:\n"
     "  -style=\"{BasedOnStyle: llvm, IndentWidth: 8}\"";
 
 static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
   if (FileName.endswith(".java"))
     return FormatStyle::LK_Java;
   if (FileName.endswith_lower(".js") || FileName.endswith_lower(".ts"))
llvm::Expected<FormatStyle> getStyle(StringRef StyleName, StringRef FileName,
   if (StyleName.startswith("{")) {
     // Parse YAML/JSON style from the command line.
     if (std::error_code ec = parseConfiguration(StyleName, &Style))
       return make_string_error("Error parsing -style: " + ec.message());
     return Style;
   }
 
   if (!StyleName.equals_lower("file")) {
+    SmallString<128> ConfigFile(StyleName.substr(5));
+    if (StyleName.startswith_lower("file,")) {
+      DEBUG(llvm::dbgs() << "Trying explicit file" << ConfigFile << "...\n");
+
+      auto Status = FS->status(ConfigFile.str());
+      bool FoundConfigFile =
+        Status && (Status->getType() == llvm::sys::fs::file_type::regular_file);
+      if (FoundConfigFile) {
+        llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Text =
+          FS->getBufferForFile(ConfigFile.str());
+        if (std::error_code EC = Text.getError()) {
+          DEBUG(llvm::dbgs() << "Text Error getting contents.\n");
+          return make_string_error(EC.message());
+        }
+        if (std::error_code ec =
+            parseConfiguration(Text.get()->getBuffer(), &Style)) {
+          if (ec == ParseError::Unsuitable) {
+
+            DEBUG(llvm::dbgs() << "Config file error.\n");
+            return make_string_error(
+                "Configuration file does not support " +
+                getLanguageName(Style.Language) + ": " +
+                ConfigFile);
+          }
+          DEBUG(llvm::dbgs() << "Error reading " << ConfigFile << ".\n");
+          return make_string_error("Error reading " + ConfigFile + ": " +
+              ec.message());
+        }
+        DEBUG(llvm::dbgs() << "Using configuration file " << ConfigFile << "\n");
+        return Style;
+      }
+      DEBUG(llvm::dbgs() << "Could not find file: " << ConfigFile << "\n");
+      return FallbackStyle;
+    }
     if (!getPredefinedStyle(StyleName, Style.Language, &Style))
       return make_string_error("Invalid value for -style");
+
+    DEBUG(llvm::dbgs() << "Using configuration file " << ConfigFile << "\n");
     return Style;
   }
 
   // Look for .clang-format/_clang-format file in the file's parent directories.
   SmallString<128> UnsuitableConfigFiles;
   SmallString<128> Path(FileName);
   if (std::error_code EC = FS->makeAbsolute(Path))
     return make_string_error(EC.message());