scons2ninja: Generate Ninja build files for SCons

About

This script generates a Ninja build file for a SCons project.

Usage

First of all, you need to do a small change to the SConstruct file of your project. This script assumes that the SConstruct has a configuration variable dump_trace, which, when set, executes the following:

env.SetOption('no_exec', True)
env.Decider(lambda x, y, z: True)
SCons.Node.Python.Value.changed_since_last_build = (lambda x, y, z: True)

(i.e. a dry run of rebuilding all files). Also make sure the command line is fully printed.

To generate the initial build.ninja file, run the following from the toplevel directory:

path/to/scons2ninja.py <optional scons flags>

This will generate the build.ninja file for an equivalent SCons build with the given flags. From then on, you can just type ninja to build. The build.ninja file will be automatically regenerated when necessary (i.e. when a SCons* file changes).

The script also reads in a .scons2ninja.conf file in the current directory, which can be used to hook your own custom steps into the process. See the example configuration file to see some customizations.

Caveats

• This script isn't fully generic yet, so there are still pretty big holes in customization and configuration.
• This script has only been tested with a very limited set of tools (gcc, clang, Visual Studio, Qt, ...). Since the script requires full knowledge of all tools run by SCons, it will fail if it finds an unsupported tool. Feel free to send a patch with support for your favorite tools.
• The script does not take into account environment variables etc. set from SCons, and the ninja build will use the current environment instead.
• Files that have dynamic content (i.e. content depending on other things than files, such as Values), will not be regenerated automatically. This is a general problem with generator-based build systems. Delete the file if you want it to be regenerated.

TODO

• Use the batching feature for SCons-generated files, when/if it is implemented in Ninja. This allows to build all SCons-generated files in one SCons invocation, saving SCons startup time for every file.

Other projects

NaCl recently added their own script for integrating Ninja with SCons. It plugs in directly into the SCons backend to get dependency information, which means it does not require full knowledge of all tools used in the build process. I will look into following a similar approach for scons2ninja, which would make it more generic and work better out of the box.