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bazel_clang_tidy

Run clang-tidy on Bazel C++ targets directly, without generating a compile commands database, and take advantage of Bazels powerful cache mechanism.

Usage:

# //:WORKSPACE
load(
    "@bazel_tools//tools/build_defs/repo:git.bzl",
    "git_repository",
)

git_repository(
       name = "bazel_clang_tidy",
       commit = "43bef6852a433f3b2a6b001daecc8bc91d791b92",
       remote = "https://github.com/erenon/bazel_clang_tidy.git",
)

You can now compile using the default clang tidy configuration provided using the following command;

bazel build //... \
  --aspects @bazel_clang_tidy//clang_tidy:clang_tidy.bzl%clang_tidy_aspect \
  --output_groups=report

If you would like to override the default clang tidy configuration then you can reconfigure the default target from the command line. To do this you must first make a filegroup target that has the .clang-tidy config file as a data dependency.

# //:BUILD
filegroup(
       name = "clang_tidy_config",
       srcs = [".clang-tidy"],
       visibility = ["//visibility:public"],
)

Now you can override the default config file in this repository using a command line flag;

bazel build //... \
  --aspects @bazel_clang_tidy//clang_tidy:clang_tidy.bzl%clang_tidy_aspect \
  --output_groups=report \
  --@bazel_clang_tidy//:clang_tidy_config=//:clang_tidy_config

❗ the config-file will not be forced by adding it to the clang-tidy command line. Therefore it must be in one of the parents of all source files. It is recommended to put it in the root directly besides the WORKSPACE file.

Now if you don't want to type this out every time, it is recommended that you add a config in your .bazelrc that matches this command line;

# Required for bazel_clang_tidy to operate as expected
build:clang-tidy --aspects @bazel_clang_tidy//clang_tidy:clang_tidy.bzl%clang_tidy_aspect
build:clang-tidy --output_groups=report

# Optionally override the .clang-tidy config file target
build:clang-tidy --@bazel_clang_tidy//:clang_tidy_config=//:clang_tidy_config

Now from the command line this is a lot nicer to use;

bazel build //... --config clang-tidy

use a non-system clang-tidy

by default, bazel_clang_tidy uses the system provided clang-tidy. If you have a hermetic build, you can use your own clang-tidy target like this:

build:clang-tidy --@bazel_clang_tidy//:clang_tidy_executable=@local_config_cc//:clangtidy_bin

This aspect is not executed on external targets. To exclude other targets, users may tag a target with no-clang-tidy or noclangtidy.

Features

  • Run clang-tidy on any C++ target
  • Run clang-tidy without also building the target
  • Use Bazel to cache clang-tidy reports: recompute stale reports only

Install

Copy .clang-tidy, BUILD and clang_tidy dir to your workspace. Edit .clang-tidy as needed.

Example

To see the tool in action:

  1. Clone the repository

  2. Run clang-tidy:

    bazel build //example --aspects clang_tidy/clang_tidy.bzl%clang_tidy_aspect --output_groups=report

  3. Check the error:

    lib.cpp:4:43: error: the parameter 'name' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param,-warnings-as-errors] std::string lib_get_greet_for(std::string name)
Aspect //clang_tidy:clang_tidy.bzl%clang_tidy_aspect of //example:app failed to build

  4. Fix the error by changing lib.cpp only.

  5. Re-run clang-tidy with the same command. Observe that it does not run clang-tidy for app.cpp: the cached report is re-used.

Requirements

  • Bazel 4.0 or newer (might work with older versions)

MongoDB-specific notes

Testing changes to this repo

To test changes to this repo, do the following:

  • Create a branch from mongodb-forks/bazel_clang_tidy (master) (e.g.: mongodb-forks/bazel_clang_tidy (test123))
  • Make and commit your changes to that branch
  • Create a branch from 10gen/mongo (master) (e.g.: 10gen/mongo (stevegrossmongodb/SERVER-12345))
  • In your 10gen/mongo branch, edit WORKSPACE.bazel as follows:
    • Comment out the http_archive(name="bazel_clang_tidy",...) call
    • Add the following portion:
load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
git_repository(
    name = "bazel_clang_tidy",
    branch = "test123", # put in the name of your mongodb-forks/bazel_clang_tidy branch here
    remote = "https://github.com/mongodb-forks/bazel_clang_tidy.git",
)
  • Now you can invoke bazel build src/... --config=clang-tidy and it will load the bazel_clang_tidy contents from your development branch.

Publishing changes to this repo

If you want to change Mongo to officially use a different version of this repo, do the following:

  • Use GitHub's UI to create a new release.
    • By default, it will use the latest revision of master (this is typically what you want)
    • For the tag id, just incremenet whatever the last one was (e.g.: v1.1 becomes v1.2)
  • In Mongo's WORKSPACE.bazel, change the http_archive(name="bazel_clang_tidy",...) call:
    • Change strip_prefix to reflect the newer version (e.g.: bazel_clang_tidy-1.1 becomes bazel_clang_tidy-1.2)
    • Change url to reflect the newer version (e.g.: https://github.com/mongodb-forks/bazel_clang_tidy/archive/refs/tags/v1.1.tar.gz becomes https://github.com/mongodb-forks/bazel_clang_tidy/archive/refs/tags/v1.2.tar.gz)