clant 1.0.2

A unified frontend for clang linting tools

Clant

Clant (CLAng liNT) is a fast and easy to use wrapper script for checking C and C++ code with the clang-based tools clang-tidy and include-what-you-use.

Though these tools are helpful, they can be tricky to configure correctly. For example, checks in headers can be mistakenly skipped, mixing C and C++ code can be a hassle, and the interface and output of the bundled wrapper scripts are inconsistent.

Clant aims to handle all of these details and provide a simple interface for running these tools on a project with nice output. Tools are run in parallel for maximum speed, and output is printed in the standard make and GCC format supported by most editors.

Example

Using Clant looks something like this:

$ cd /mylib
$ clant
clant: Entering directory `/mylib/build'
clant: Loading compilation database `compile_commands.json'
../include/mylib/mylib.h:1:1: note: includes are correct
../src/mylib.c:239:1: error: function 'run' has a definition with different parameter names [readability-inconsistent-declaration-parameter-name,-warnings-as-errors]
run(Thing* result);
^
../src/mylib.c:576:1: note: the definition seen here
run(Thing* out)
^
../src/rerex.c:239:1: note: differing parameters are named here: ('result'), in definition: ('out')
run(Something* result);
^              ~~~~~~
               out

../test/test_something.c:26:1: error: remove this line
#include <stdlib.h>
../test/test_something.c:1:1: note: code is tidy
clant: Leaving directory `/mylib/build/build'

Installation

Clant is a Python script that can simply be run anywhere, installation is not necessary.

It can, however, be installed with pip:

pip install clant

Installation from the source directory is also possible:

cd path_to_clant_source
pip install .

Usage

Ideally, you can simply run clant from your project directory:

cd path_to_my_project
clant

Clant will assume that a build exists in the build subdirectory, and look for compile_commands.json there. To use a different build directory, pass it as a parameter:

clant release

By default, the number of threads supported by the CPU will be used. To use a different number of threads, use the -j option:

clant -j 4

Individual tools can be disabled for faster runs or to suppress warnings while working on issues:

clant --no-tidy
clant --no-iwyu

Checking Headers

Clant attempts to run tools in a way that automatically includes appropriate headers in checks, but this may miss headers that are not included in the build, or that are not inside the project directory. Additional headers can be checked by providing include directories with the --include option. This will run checks on all the headers in that directory, recursively:

clant --include include

Include Mapping Files

Mapping files are supported by include-what-you-use to specify include file mappings for third-party libraries or other things that the tool does not automatically understand. Additional mapping files can be given with the --mapping option:

clant --mapping /path/to/somelibrary.imp
clant --mapping someotherlibrary.imp

If they are not absolute paths, mapping files will be searched for first in the project directory, then in the system include-what-you-use directory (relative to the binary, typically /usr/share/include-what-you-use).

Excluding Files

Sometimes, certain files can't be realistically changed to reach the same level of cleanliness as the rest of the project, for example generated or third-party code. Such files can be excluded by providing a regular expression with the --exclude option:

clant --exclude '.*generated.*\.c'

Warnings

Warnings are configured using the standard .clang-tidy mechanism. The simplest approach is to simply add a single .clang-tidy file to the project root, and enable or suppress any warnings there.

To be more fine-grained, for example to specify stricter warnings for headers than implementations, separate files can be used. The .clang-tidy file in the closest parent directory to the source being checked will be used. Note, however, that clang-tidy does not check headers on their own by default, and that included headers will be checked using the settings for that compilation (including the language), not the .clang-tidy file associated with the header.

This can be especially tricky for projects that contain both C and C++. To get around this problem, unless the --no-auto-headers option is given, Clant automatically includes headers of the matching language based on their extension, which overrides the HeaderFilterRegex option in the .clang-tidy file. This prevents C++ warnings from being produced for C headers, or vice-versa. For C sources with extension .c, any included .h files within the project are checked. For C++ sources with extension .cpp or .cc, any included .hh, .hpp, or .ipp files within the project are checked.

The extra headers given with the --include option are always checked on their own, avoiding these issues. Since there is no associated command in the compilation database for headers, Clant combines all of the include paths given to any compile command to run tools on these headers.

Using from Python

Clant is also installed as a Python package called clant, which contains a single module, also called clant.

The command-line utility is implemented in clant.main(), which takes no arguments since they are read from sys.argv.

That is a simple wrapper for clant.run(), which takes parameters that loosely correspond with command line parameters, but using lists for multiple values and more appropriate names. Only build_dir is required. For example:

from clant import clant

clant.run(auto_headers=True,
          build_dir="build",
          exclude_patterns=[".*gen.*"],
          iwyu=False,
          jobs=4,
          mapping_files=["qt5_11.imp"],
          tidy=True,
          verbose=False)

Configuration File

A configuration can be included in a project by adding a .clant.json file in the project root directory. This file must be a JSON object, where the keys correspond to the keyword parameters of clant.run() described above.

The one exception is the version key, which must be present, and represents the version of Clant the configuration file is for. Currently, this is only used to print a warning if the configuration is newer, but it may be used in the future to handle any potential compatibility issues.

For example, this configuration uses all of the supported keys:

{
  "auto_headers": true,
  "build_dir": "release",
  "exclude_patterns": [".*gen.*"],
  "iwyu": false,
  "jobs": 4,
  "mapping_files": ["qt5_11.imp"],
  "tidy": true,
  "verbose": false,
  "version": "1.0.0"
}

If command line parameters are also given, then values from the configuration file will override them, except for lists, which will be added.

Assumptions

Aside from some of the defaults described above, Clant is a somewhat opinionated tool that assumes a few things for ease of use:

• clang-tidy and include-what-you-use are installed, that is, these commands are available in the PATH.

• The build directory is an immediate child of the project directory.

• The build directory contains a valid JSON Compilation Database named compile_commands.json.

• For the auto headers feature:

  • C sources have extension .c, C headers have extension .h.

  • C++ sources have extension .cpp or .cc, C++ headers have extension .hpp, .hh, or .ipp.

• For checking extra headers:

  • Headers can be "compiled" by including every -I given to every compile command, so there are no conflicting header names.

Feel free to submit a patch if any of these are problematic for you.

-- David Robillard [e-mail]