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Clang Tidy

[TOC]

Danger, Will Robinson!

Support for clang-tidy in Chromium is very experimental, and is somewhat painful to use. We are exploring making it easier and integrating with existing tools, but aren't there yet. If you don't want to wait and enjoy tinkering, forge ahead. Otherwise, feel free to turn back now.

Introduction

clang-tidy is a clang-based C++ “linter” tool. Its purpose is to provide an extensible framework for diagnosing and fixing typical programming errors, like style violations, interface misuse, or bugs that can be deduced via static analysis.

Setting Up

Automatic Setup

The script clang_tidy_tool.py will automatically fetch, build, and invoke clang-tidy. To do this manually, follow the steps in the next section.

Manual Setup

In addition to a full Chromium checkout, you need the clang-tidy binary. We recommend checking llvm's clang source and building the clang-tidy binary directly. Instructions for getting started with clang are available from llvm. You'll need to get llvm, clang, and the extra clang tools (you won't need Compiler-RT or libcxx). If you don't have it, you'll also need to install CMake as a part of this process.

Instead of building with "Unix Makefiles", generate build files for Ninja with

cmake -GNinja \
    -DLLVM_ENABLE_PROJECTS=clang;clang-tools-extra \
    -DCMAKE_BUILD_TYPE=Release \
    ../llvm

Then, instead of using make, use ninja to build the clang-tidy binary with

ninja clang-tidy

This binary will be at (build)/bin/clang-tidy.

If you intend to use the fix feature of clang-tidy, you'll also need to build the clang-apply-replacements binary.

ninja clang-apply-replacements

Running clang-tidy

Running clang-tidy is (hopefully) simple.

  1. Build chrome normally.
ninja -C out/Release chrome
  1. Generate the compilation database
tools/clang/scripts/generate_compdb.py -p out/Release > out/Release/compile_commands.json
  1. Enter the build directory.
cd out/Release
  1. Run clang-tidy.
<PATH_TO_LLVM_SRC>/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py \
    -p . \# Set the root project directory, where compile_commands.json is.
    # Set the clang-tidy binary path, if it's not in your $PATH.
    -clang-tidy-binary <PATH_TO_LLVM_BUILD>/bin/clang-tidy \
    # Set the clang-apply-replacements binary path, if it's not in your $PATH
    # and you are using the `fix` behavior of clang-tidy.
    -clang-apply-replacements-binary \
        <PATH_TO_LLVM_BUILD>/bin/clang-apply-replacements \
    # The checks to employ in the build. Use `-*` to omit default checks.
    -checks=<CHECKS> \
    -header-filter=<FILTER> \# Optional, limit results to only certain files.
    -fix \# Optional, used if you want to have clang-tidy auto-fix errors.
    chrome/browser # The path to the files you want to check.

Copy-Paste Friendly (though you'll still need to stub in the variables):
<PATH_TO_LLVM_SRC>/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py \
    -p . \
    -clang-tidy-binary <PATH_TO_LLVM_BUILD>/bin/clang-tidy \
    -clang-apply-replacements-binary \
        <PATH_TO_LLVM_BUILD>/bin/clang-apply-replacements \
    -checks=<CHECKS> \
    -header-filter=<FILTER> \
    -fix \
    chrome/browser

*It's not clear which, if any, gn flags may cause issues for clang-tidy. I've had no problems building a component release build, both with and without goma. if you run into issues, let us know!

Questions

Questions? Reach out to rdevlin.cronin@chromium.org or thakis@chromium.org. Discoveries? Update the doc!