Aren't build hooks inherently thread unsafe due to the requirement that they be called in the source directory? You do not pass the source directory into the build hook, it's not part of the interface defined in PEP 517. So the build hook must require the working directory be the source directory. You look up the pyproject.toml by cwd when implementing a hook, as well as whatever it is supposed to build.

A redundant change is fine to remove, but there is always at least one, right?

(I'm thinking of doing multiple builds at the same time - ahh, maybe that's not what you are working on here.)

A redundant change is fine to remove, but there is always at least one, right?

Do you mean that there is at least one os.chdir in the current thread/process? There isn't, build hooks are executed in a subprocess with the cwd set to the project root.

Thanks for this. Can you add a simple test to validate that a relative path is made absolute by the ProjectBuilder constructor?

I'll rebase this on top of #532 as soon as it's unblocked, don't bother fixing the line no :)

Actually, can you rebase on top of main, @radoering? I don't want to rewrite your history.

Thanks!