[clang-tidy] Make format style customizable

Summary: I came across an outstanding FIXME to make the format style customizable. Inspired by the include fixer, I added an new option `-style` to configure the fallback style in case no clang-format configuration file is found. The default remains "llvm". 

Reviewers: Prazek, aaron.ballman, hokein, alexfh

Subscribers: cfe-commits, malcolm.parsons

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D27142

llvm-svn: 288258
diff --git a/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp b/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
index 8578ef4..fd53c4e 100644
--- a/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
+++ b/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
@@ -49,9 +49,9 @@
 
 )");
 
-const char DefaultChecks[] =  // Enable these checks by default:
-    "clang-diagnostic-*,"     //   * compiler diagnostics
-    "clang-analyzer-*";       //   * Static Analyzer checks
+const char DefaultChecks[] = // Enable these checks by default:
+    "clang-diagnostic-*,"    //   * compiler diagnostics
+    "clang-analyzer-*";      //   * Static Analyzer checks
 
 static cl::opt<std::string> Checks("checks", cl::desc(R"(
 Comma-separated list of globs with optional '-'
@@ -120,6 +120,13 @@
 )"),
                                cl::init(false), cl::cat(ClangTidyCategory));
 
+static cl::opt<std::string> FormatStyle("style", cl::desc(R"(
+Fallback style for reformatting after inserting fixes
+if there is no clang-format config file found.
+)"),
+                                        cl::init("llvm"),
+                                        cl::cat(ClangTidyCategory));
+
 static cl::opt<bool> ListChecks("list-checks", cl::desc(R"(
 List all enabled checks and exit. Use with
 -checks=* to list all available checks.
@@ -386,7 +393,8 @@
   unsigned WErrorCount = 0;
 
   // -fix-errors implies -fix.
-  handleErrors(Errors, (FixErrors || Fix) && !DisableFixes, WErrorCount);
+  handleErrors(Errors, (FixErrors || Fix) && !DisableFixes, FormatStyle,
+               WErrorCount);
 
   if (!ExportFixes.empty() && !Errors.empty()) {
     std::error_code EC;