[clang-tidy] Add library for clang-tidy main function

Summary:
This library allows to create clang-tidy tools with custom checks outside of llvm repo
using prebuilt clang release tarball.

Test Plan:
Checked that clang-tidy works as before. New library exists in istall dir.

Reviewers: smeenai, gribozavr, stephanemoore

Subscribers: mgorny, xazax.hun, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D73300

clang-tools-extra/clang-tidy/tool/CMakeLists.txt

@@ -5,8 +5,24 @@ set(LLVM_LINK_COMPONENTS
   support
   )
 
-add_clang_tool(clang-tidy
+# Needed by LLVM's CMake checks because this file defines multiple targets.
+set(LLVM_OPTIONAL_SOURCES ClangTidyMain.cpp ClangTidyToolMain.cpp)
+
+add_clang_library(clangTidyMain
   ClangTidyMain.cpp
+
+  LINK_LIBS
+  clangAST
+  clangASTMatchers
+  clangBasic
+  clangTidy
+  ${ALL_CLANG_TIDY_CHECKS}
+  clangTooling
+  clangToolingCore
+  )
+
+add_clang_tool(clang-tidy
+  ClangTidyToolMain.cpp
   )
 add_dependencies(clang-tidy
   clang-resource-headers
@@ -22,6 +38,7 @@ clang_target_link_libraries(clang-tidy
 target_link_libraries(clang-tidy
   PRIVATE
   clangTidy
+  clangTidyMain
   ${ALL_CLANG_TIDY_CHECKS}
   )
 

clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp

@@ -14,6 +14,7 @@
 ///
 //===----------------------------------------------------------------------===//
 
+#include "ClangTidyMain.h"
 #include "../ClangTidy.h"
 #include "../ClangTidyForceLinker.h"
 #include "../GlobList.h"
@@ -327,7 +328,7 @@ getVfsFromFile(const std::string &OverlayFile,
   return FS;
 }
 
-static int clangTidyMain(int argc, const char **argv) {
+int clangTidyMain(int argc, const char **argv) {
   llvm::InitLLVM X(argc, argv);
   CommonOptionsParser OptionsParser(argc, argv, ClangTidyCategory,
                                     cl::ZeroOrMore);
@@ -488,7 +489,3 @@ static int clangTidyMain(int argc, const char **argv) {
 
 } // namespace tidy
 } // namespace clang
-
-int main(int argc, const char **argv) {
-  return clang::tidy::clangTidyMain(argc, argv);
-}

clang-tools-extra/clang-tidy/tool/ClangTidyMain.h

@@ -0,0 +1,23 @@
+//===--- tools/extra/clang-tidy/ClangTidyMain.h - Clang tidy tool -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+///  \file This file declares the main function for the clang-tidy tool.
+///
+///  This tool uses the Clang Tooling infrastructure, see
+///    http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html
+///  for details on setting it up with LLVM source tree.
+///
+//===----------------------------------------------------------------------===//
+
+namespace clang {
+namespace tidy {
+
+int clangTidyMain(int argc, const char **argv);
+
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/tool/ClangTidyToolMain.cpp

@@ -0,0 +1,21 @@
+//===--- tools/extra/clang-tidy/ClangTidyToolMain.cpp - Clang tidy tool ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+///  \file This file contains clang-tidy tool entry point main function.
+///
+///  This tool uses the Clang Tooling infrastructure, see
+///    http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html
+///  for details on setting it up with LLVM source tree.
+///
+//===----------------------------------------------------------------------===//
+
+#include "ClangTidyMain.h"
+
+int main(int argc, const char **argv) {
+  return clang::tidy::clangTidyMain(argc, argv);
+}