On Thu, Jun 28, 2018, at 8:25 AM, Paul Moore wrote:
> I can see the practicality argument here. I don't think (correct me if
> I'm wrong!) that anyone particularly anticipated when we were drafting
> PEP 518 that the tools section would be used by anything other than
> build tools - I know I hadn't anticipated that usage. In hindsight
> it's an obvious thing to do, but it does mean that pyproject.toml is
> more of a "general project configuration" file than purely a build
> configuration one.
I agree - I didn't really think about this, but it is obvious in hindsight: we provide one obvious place to put configuration, and people put it there. :-)
The file was originally meant to target building wheels for libraries. It just happens that folks have pushed that out to include apps as well. So if the purpose of the file expands to include apps as well then that changes what the PEP should require to be in the file.
Maybe pip should be switching behaviour based on the presence of the [build-system] table in the toml file, rather than just the presence of pyproject.toml?
If the decision is to make having the value optional then I agree there should be 2 code paths: isolated based on pyproject.toml and build requirements specified, or the old way. I would also consider continuing to issue a warning for the lack of details in pyproject.toml (and maybe lacking pyproject.toml some day?).