Reland "enable plugins for clang-tidy"

This reverts commit ab3b898 but
disables the new test if the user has disabled support for building it.

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

@@ -29,11 +29,17 @@ clang_target_link_libraries(clangTidyMain
   clangToolingCore
   )
 
+# Support plugins.
+if(CLANG_PLUGIN_SUPPORT)
+  set(support_plugins SUPPORT_PLUGINS)
+endif()
+
 add_clang_tool(clang-tidy
   ClangTidyToolMain.cpp
-  )
-add_dependencies(clang-tidy
+
+  DEPENDS
   clang-resource-headers
+  ${support_plugins}
   )
 clang_target_link_libraries(clang-tidy
   PRIVATE
@@ -50,6 +56,9 @@ target_link_libraries(clang-tidy
   ${ALL_CLANG_TIDY_CHECKS}
   )
 
+if(CLANG_PLUGIN_SUPPORT)
+  export_executable_symbols_for_plugins(clang-tidy)
+endif()
 
 install(PROGRAMS clang-tidy-diff.py
   DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"

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

@@ -20,6 +20,7 @@
 #include "../GlobList.h"
 #include "clang/Tooling/CommonOptionsParser.h"
 #include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
@@ -386,6 +387,11 @@ getVfsFromFile(const std::string &OverlayFile,
 
 int clangTidyMain(int argc, const char **argv) {
   llvm::InitLLVM X(argc, argv);
+
+  // Enable help for -load option, if plugins are enabled.
+  if (cl::Option *LoadOpt = cl::getRegisteredOptions().lookup("load"))
+    LoadOpt->addCategory(ClangTidyCategory);
+
   llvm::Expected<CommonOptionsParser> OptionsParser =
       CommonOptionsParser::create(argc, argv, ClangTidyCategory,
                                   cl::ZeroOrMore);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -207,6 +207,8 @@ Improvements to clang-tidy
 - Added support for `NOLINTBEGIN` ... `NOLINTEND` comments to suppress
   Clang-Tidy warnings over multiple lines.
 
+- Added support for external plugin checks with `-load`.
+
 New checks
 ^^^^^^^^^^
 

clang-tools-extra/docs/clang-tidy/Contributing.rst

@@ -634,6 +634,26 @@ This keeps the test directory from getting cluttered.
 .. _FileCheck: https://llvm.org/docs/CommandGuide/FileCheck.html
 .. _test/clang-tidy/google-readability-casting.cpp: https://reviews.llvm.org/diffusion/L/browse/clang-tools-extra/trunk/test/clang-tidy/google-readability-casting.cpp
 
+Out-of-tree check plugins
+-------------------------
+
+Developing an out-of-tree check as a plugin largely follows the steps
+outlined above. The plugin is a shared library whose code lives outside
+the clang-tidy build system. Build and link this shared library against
+LLVM as done for other kinds of Clang plugins.
+
+The plugin can be loaded by passing `-load` to `clang-tidy` in addition to the
+names of the checks to enable.
+
+.. code-block:: console
+
+  $ clang-tidy --checks=-*,my-explicit-constructor -list-checks -load myplugin.so
+
+There is no expectations regarding ABI and API stability, so the plugin must be
+compiled against the version of clang-tidy that will be loading the plugin.
+
+The plugins can use threads, TLS, or any other facilities available to in-tree
+code which is accessible from the external headers.
 
 Running clang-tidy on LLVM
 --------------------------

clang-tools-extra/docs/clang-tidy/index.rst

@@ -218,6 +218,15 @@ An overview of all the command-line options:
     --list-checks                  -
                                      List all enabled checks and exit. Use with
                                      -checks=* to list all available checks.
+    -load=<plugin>                 -
+                                     Load the dynamic object ``plugin``. This
+                                     object should register new static analyzer
+                                     or clang-tidy passes. Once loaded, the
+                                     object will add new command line options
+                                     to run various analyses. To see the new
+                                     complete list of passes, use the
+                                     :option:`--list-checks` and
+                                     :option:`-load` options together.
     -p=<string>                    - Build path
     --quiet                        -
                                      Run clang-tidy in quiet mode. This suppresses

clang-tools-extra/test/CMakeLists.txt

@@ -17,6 +17,8 @@ string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} CLANG_TOOLS_DIR ${LLVM_RUN
 
 llvm_canonicalize_cmake_booleans(
   CLANG_TIDY_ENABLE_STATIC_ANALYZER
+  LLVM_ENABLE_PLUGINS
+  LLVM_INSTALL_TOOLCHAIN_ONLY
   )
 
 configure_lit_site_cfg(
@@ -78,6 +80,24 @@ foreach(dep ${LLVM_UTILS_DEPS})
   endif()
 endforeach()
 
+if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
+  llvm_add_library(
+      CTTestTidyModule
+      MODULE clang-tidy/CTTestTidyModule.cpp
+      PLUGIN_TOOL clang-tidy
+      DEPENDS clang-tidy-headers)
+
+  if(TARGET CTTestTidyModule)
+      list(APPEND CLANG_TOOLS_TEST_DEPS CTTestTidyModule LLVMHello)
+      target_include_directories(CTTestTidyModule PUBLIC BEFORE "${CLANG_TOOLS_SOURCE_DIR}")
+      if(LLVM_ENABLE_PLUGINS AND (WIN32 OR CYGWIN))
+        set(LLVM_LINK_COMPONENTS
+          Support
+        )
+      endif()
+  endif()
+endif()
+
 add_lit_testsuite(check-clang-tools "Running the Clang extra tools' regression tests"
   ${CMAKE_CURRENT_BINARY_DIR}
   DEPENDS ${CLANG_TOOLS_TEST_DEPS}

clang-tools-extra/test/clang-tidy/CTTestTidyModule.cpp

@@ -0,0 +1,66 @@
+// REQUIRES: plugins
+// RUN: clang-tidy -checks='-*,mytest*' --list-checks -load %llvmshlibdir/CTTestTidyModule%pluginext -load %llvmshlibdir/LLVMHello%pluginext | FileCheck --check-prefix=CHECK-LIST %s
+// CHECK-LIST: Enabled checks:
+// CHECK-LIST-NEXT:    mytest1
+// CHECK-LIST-NEXT:    mytest2
+// RUN: clang-tidy -checks='-*,mytest*,misc-definitions-in-headers' -load %llvmshlibdir/CTTestTidyModule%pluginext /dev/null -- -xc 2>&1 | FileCheck %s
+// CHECK: 3 warnings generated.
+// CHECK-NEXT: warning: mytest success [misc-definitions-in-headers,mytest1,mytest2]
+
+#include "clang-tidy/ClangTidy.h"
+#include "clang-tidy/ClangTidyCheck.h"
+#include "clang-tidy/ClangTidyModule.h"
+#include "clang-tidy/ClangTidyModuleRegistry.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang;
+using namespace clang::tidy;
+using namespace clang::ast_matchers;
+
+namespace {
+class MyTestCheck : public ClangTidyCheck {
+
+public:
+  MyTestCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override {
+    Finder->addMatcher(translationUnitDecl().bind("tu"), this);
+  }
+
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override {
+    auto S = Result.Nodes.getNodeAs<TranslationUnitDecl>("tu");
+    if (S)
+      diag("mytest success");
+  }
+
+private:
+};
+
+class CTTestModule : public ClangTidyModule {
+public:
+  void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<MyTestCheck>("mytest1");
+    CheckFactories.registerCheck<MyTestCheck>("mytest2");
+    // intentionally collide with an existing test name, overriding it
+    CheckFactories.registerCheck<MyTestCheck>("misc-definitions-in-headers");
+  }
+};
+} // namespace
+
+namespace tidy1 {
+// Register the CTTestTidyModule using this statically initialized variable.
+static ClangTidyModuleRegistry::Add<::CTTestModule>
+    X("mytest-module", "Adds my checks.");
+} // namespace tidy1
+
+namespace tidy2 {
+// intentionally collide with an existing test group name, merging with it
+static ClangTidyModuleRegistry::Add<::CTTestModule>
+    X("misc-module", "Adds miscellaneous lint checks.");
+} // namespace tidy2
+
+// This anchor is used to force the linker to link in the generated object file
+// and thus register the CTTestModule.
+volatile int CTTestModuleAnchorSource = 0;

clang-tools-extra/test/lit.cfg.py

@@ -149,3 +149,9 @@
                                      "clangd", "benchmarks")
 config.substitutions.append(('%clangd-benchmark-dir',
                              '%s' % (clangd_benchmarks_dir)))
+config.substitutions.append(('%llvmshlibdir', config.clang_libs_dir))
+config.substitutions.append(('%pluginext', config.llvm_plugin_ext))
+
+# Plugins (loadable modules)
+if config.has_plugins and config.llvm_plugin_ext:
+    config.available_features.add('plugins')

clang-tools-extra/test/lit.site.cfg.py.in

@@ -4,13 +4,15 @@ import sys
 
 config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
 config.llvm_libs_dir = "@LLVM_LIBS_DIR@"
+config.llvm_plugin_ext = "@LLVM_PLUGIN_EXT@"
 config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
 config.clang_tools_binary_dir = "@CLANG_TOOLS_BINARY_DIR@"
 config.clang_tools_dir = "@CLANG_TOOLS_DIR@"
 config.clang_libs_dir = "@SHLIBDIR@"
 config.python_executable = "@Python3_EXECUTABLE@"
 config.target_triple = "@TARGET_TRIPLE@"
 config.clang_tidy_staticanalyzer = @CLANG_TIDY_ENABLE_STATIC_ANALYZER@
+config.has_plugins = @LLVM_ENABLE_PLUGINS@ & ~@LLVM_INSTALL_TOOLCHAIN_ONLY@
 
 # Support substitution of the tools and libs dirs with user parameters. This is
 # used when we can't determine the tool dir at configuration time.