When reading about how ninja, one of my first thoughts was that why not use ninja itself bootstrap the build.ninja file?

I tried googling this topic, but haven't really found anything, other than some closed issues concerning problems when regenerating build.ninja, but nothing directly about using a build.ninja-stub to bootstrap the project.

Looking at the build.ninja of this project, it at least contains a passage to regenerate its contents when ./configure is changed:

# Regenerate build files if build script changes.
rule configure
  command = ${configure_env}python3 $root/configure.py $configure_args
  generator = 1
build build.ninja: configure | $root/configure.py $root/misc/ninja_syntax.py

So my questions are:

Why not have that part in an otherwise empty build.ninja, so that the user can just run ninja the first time and the project bootstraps itself?

Does the build.ninja get reloaded by the running ninja process when it changes?
As in would running ninja manual succeed in generating doc/manual.html?

If the answer to these questions is "yes" it would be nice for those details to be part of the manual and maybe documented as potential pattern to use to bootstrap projects.

Though arguably writing to a source-controlled file might be a bad idea, instead one could write to an build.ninja file contained in the build directory and include that? (Does changing those cause ninja re-source them? And would ninja run when the file path doesn't exist currently, but is defined as a build target?)

If the answer is "no", it would be good to document that as gotcha and might be a potentially neat feature to consider in the future.

I would of cause be open to discuss this topic either here, or on the mailing list.