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ClangPlugins.rst

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Clang Plugins

NOTE: this document applies to the original Clang project, not the DirectX Compiler. It's made available for informational purposes only.

Clang Plugins make it possible to run extra user defined actions during a compilation. This document will provide a basic walkthrough of how to write and run a Clang Plugin.

Introduction

Clang Plugins run FrontendActions over code. See the :doc:`FrontendAction tutorial <RAVFrontendAction>` on how to write a FrontendAction using the RecursiveASTVisitor. In this tutorial, we'll demonstrate how to write a simple clang plugin.

Writing a PluginASTAction

The main difference from writing normal FrontendActions is that you can handle plugin command line options. The PluginASTAction base class declares a ParseArgs method which you have to implement in your plugin.

bool ParseArgs(const CompilerInstance &CI,
               const std::vector<std::string>& args) {
  for (unsigned i = 0, e = args.size(); i != e; ++i) {
    if (args[i] == "-some-arg") {
      // Handle the command line argument.
    }
  }
  return true;
}

Registering a plugin

A plugin is loaded from a dynamic library at runtime by the compiler. To register a plugin in a library, use FrontendPluginRegistry::Add<>:

static FrontendPluginRegistry::Add<MyPlugin> X("my-plugin-name", "my plugin description");

Putting it all together

Let's look at an example plugin that prints top-level function names. This example is checked into the clang repository; please take a look at the latest version of PrintFunctionNames.cpp.

Running the plugin

To run a plugin, the dynamic library containing the plugin registry must be loaded via the :option:`-load` command line option. This will load all plugins that are registered, and you can select the plugins to run by specifying the :option:`-plugin` option. Additional parameters for the plugins can be passed with :option:`-plugin-arg-<plugin-name>`.

Note that those options must reach clang's cc1 process. There are two ways to do so:

  • Directly call the parsing process by using the :option:`-cc1` option; this has the downside of not configuring the default header search paths, so you'll need to specify the full system path configuration on the command line.
  • Use clang as usual, but prefix all arguments to the cc1 process with :option:`-Xclang`.

For example, to run the print-function-names plugin over a source file in clang, first build the plugin, and then call clang with the plugin from the source tree:

$ export BD=/path/to/build/directory
$ (cd $BD && make PrintFunctionNames )
$ clang++ -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS \
          -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -D_GNU_SOURCE \
          -I$BD/tools/clang/include -Itools/clang/include -I$BD/include -Iinclude \
          tools/clang/tools/clang-check/ClangCheck.cpp -fsyntax-only \
          -Xclang -load -Xclang $BD/lib/PrintFunctionNames.so -Xclang \
          -plugin -Xclang print-fns

Also see the print-function-name plugin example's README