cja

A CMake-compatible build system that generates Ninja build files.

Build a project with a CMakeLists.txt using:

cja
ninja

This is equivalent to the following with CMake:

cmake -Bbuild -GNinja -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_COLOR_DIAGNOSTICS=1 -DCMAKE_EXPORT_COMPILE_COMMANDS=1
ninja -Cbuild

Install

pip install cja

Or, if you're in a managed Python environment:

pipx install cja

Comparison to CMake

• The build.ninja file is generated in your project root, not in the build directory. To allow multiple build configurations in parallel, the file name is <builddir>.ninja.
• Paths are relative to the project root, while CMake uses absolute paths. This is faster, reduces output, and also reduces binary size as paths (e.g. for debug symbols) are shorter. When reading output from a Docker container, this lets you click paths and open the correct files in your local editor.
• Instead of a separate tool like CTest, cja generates a phony test target that runs all tests as part of the Ninja build graph, so tests can start as soon as the first test binary is ready. Tests run one after another in Ninja's console pool; test-parallel (or cja test --parallel) runs them in parallel instead.
• Colors for compiler diagnostics are enabled by default.
• _builddir_/compile_commands.json is always generated.
• More colorful, simplified output. For example, when downloading dependencies, cja shows progress bars using Rich, while CMake shows no output (or simple multi-line output when -DFETCHCONTENT_QUIET=0 is specified).

Limitations to keep cja simple:

• Only generates Ninja build files.
• Out-of-tree builds aren't allowed.
• Only supports Linux, macOS, and Windows.
• Only supports clang with a GNU-like command line on Windows.

Build Subcommand

cja supports a build subcommand, which runs ninja automatically afterward.

cja --release / cja build --release

cja --release is equivalent to:

cja -Bbuild-release -DCMAKE_BUILD_TYPE=Release

cja build --release additionally runs ninja:

cja -Bbuild-release -DCMAKE_BUILD_TYPE=Release
ninja -f build-release.ninja

Run Subcommand

cja also generates a run phony target that executes the first executable (or the one set via VS_STARTUP_PROJECT) in your CMakeLists.txt.

Format Subcommand

cja format formats CMake files, similar to cmake-format or clang-format:

cja format CMakeLists.txt               # print the formatted file
cja format -i CMakeLists.txt foo.cmake  # format files in place
cja format --check CMakeLists.txt       # exit with 1 if the file isn't formatted

Without file arguments it reads from stdin (use --assume-filename to tell it where the file lives).

There is no configuration file of its own. Instead, these options are read from the nearest .clang-format:

• IndentWidth, UseTab and TabWidth
• ColumnLimit (0 means no limit)
• MaxEmptyLinesToKeep
• LineEnding
• BasedOnStyle (for the defaults of the options above) and DisableFormat

Everything else follows cmake-format's defaults, with a few differences:

• A command call that fits on one line is kept on one line, like clang-format does (cmake-format breaks calls with more than two argument groups or six arguments).
• Comments are never reflowed.
• The names of user-defined commands keep their spelling (builtin commands are still lowercased) and UPPERCASE words in their arguments are treated as keywords.
• Line endings and a UTF-8 BOM are preserved.

Use # cmake-format: off / # cmake-format: on (or # clang-format off / on) to exclude a region.