ja runs ninja in the background. When the first failure occurs (e.g. a file failed to compile) it will display it’s output and exit. When a file has a syntax error, you can therefore immediately reuse the command prompt to edit the file without having to wait for other jobs to finish (they will run in the background though).
ja locks the build directory so that you won’t be able to accidentely compile twice, e.g. in different terminals.
ja will display a jobs description with colors, similar to CMake’s
make output. That way you can
easily distinguish compiling from linking, etc.
A nice progress bar makes compiling fun! Also ja will display an approximation of the time left. But when your build has failed ja won’t display any unneeded information as your compiler messages include everything that’s needed anyway.
When running ja from a directory without out a
ninja.build file, but with a
meson.build file, it will create a
build/ directory for you, run
cmake -GNinja .. or
meson .. inside that directory and start building after that.
ninja status output shows you the command which was started last. When a previous command gets stuck, you won’t be able to identify it though (see ninja bug #1158)! ja avoids this problem by always showing a command that is still running in its status output.
ja is NOT a fork of ninja, it’s a frontend written in Python which runs alongside. Until ninja PR #1210 is merged you’ll need to build ninja from source though:
git clone https://github.com/jhasse/ninja cd ninja git checkout serialize ./configure.py --bootstrap sudo install ninja /usr/local/bin
ja can be installed via Python’s package manager:
sudo pip3 install ja
Or check out the source on GitHub.