[clang-format] Add a default format style that can be used by users of `getStyle`

Summary:
Tools that reformat code often call `getStyle` to decide the format style
to use on a certain source file. In practice, "file" style is widely used. As a
result, many tools hardcode "file" when calling `getStyle`, which makes it hard
to control the default style in tools across a codebase when needed. This change
introduces a `DefaultFormatStyle` constant (default to "file" in upstream), which
can be modified downstream if wanted, so that all users/tools built from the same
source tree can have a consistent default format style.

This also adds an DefaultFallbackStyle that is recommended to be used by tools and can be modified downstream.

Reviewers: sammccall, djasper

Reviewed By: sammccall

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D48492

llvm-svn: 335492

3 files changed, 24 insertions, 10 deletions

diff --git a/clang/include/clang/Format/Format.h b/clang/include/clang/Format/Format.h
index 1d135fe1bd2..36616e556a9 100644
--- a/clang/include/clang/Format/Format.h
+++ b/clang/include/clang/Format/Format.h
@@ -1963,6 +1963,15 @@ LangOptions getFormattingLangOpts(const FormatStyle &Style = getLLVMStyle());
 /// of ``getStyle()``.
 extern const char *StyleOptionHelpDescription;
 
+/// The suggested format style to use by default. This allows tools using
+/// `getStyle` to have a consistent default style.
+/// Different builds can modify the value to the preferred styles.
+extern const char *DefaultFormatStyle;
+
+/// The suggested predefined style to use as the fallback style in `getStyle`.
+/// Different builds can modify the value to the preferred styles.
+extern const char *DefaultFallbackStyle;
+
 /// Construct a FormatStyle based on ``StyleName``.
 ///
 /// ``StyleName`` can take several forms:
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 76dfc819507..374c25064a9 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -2144,6 +2144,10 @@ FormatStyle::LanguageKind guessLanguage(StringRef FileName, StringRef Code) {
   return GuessedLanguage;
 }
 
+const char *DefaultFormatStyle = "file";
+
+const char *DefaultFallbackStyle = "LLVM";
+
 llvm::Expected<FormatStyle> getStyle(StringRef StyleName, StringRef FileName,
                                      StringRef FallbackStyleName,
                                      StringRef Code, vfs::FileSystem *FS) {
diff --git a/clang/tools/clang-format/ClangFormat.cpp b/clang/tools/clang-format/ClangFormat.cpp
index fdd0c41d08e..de2f9d7fe76 100644
--- a/clang/tools/clang-format/ClangFormat.cpp
+++ b/clang/tools/clang-format/ClangFormat.cpp
@@ -60,17 +60,18 @@ LineRanges("lines", cl::desc("<start line>:<end line> - format a range of\n"
                              "Can only be used with one input file."),
            cl::cat(ClangFormatCategory));
 static cl::opt<std::string>
-    Style("style",
-          cl::desc(clang::format::StyleOptionHelpDescription),
-          cl::init("file"), cl::cat(ClangFormatCategory));
+    Style("style", cl::desc(clang::format::StyleOptionHelpDescription),
+          cl::init(clang::format::DefaultFormatStyle),
+          cl::cat(ClangFormatCategory));
 static cl::opt<std::string>
-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.\n"
-                       "Use -fallback-style=none to skip formatting."),
-              cl::init("LLVM"), cl::cat(ClangFormatCategory));
+    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.\n"
+                           "Use -fallback-style=none to skip formatting."),
+                  cl::init(clang::format::DefaultFallbackStyle),
+                  cl::cat(ClangFormatCategory));
 
 static cl::opt<std::string>
 AssumeFileName("assume-filename",