[FR] Target segment position bump custom callable/hook support

[webknjaz]

So I've been thinking about making an automation with Towncrier where setuptools-scm would be made aware of which segment should be updated when guessing the next version.

I know there are multiple strategies available, but they are all pretty much hardcoded. What I want is to keep using a strategy that's already available but be able to tell setuptools-scm whether the next guessed version would bump MAJOR, MINOR, PATCH or whatever segment bit.

What I was imagining is a sort of a setting that would allow pointing at an arbitrary callable (typically in-tree) that would return an integer telling setuptools-scm which part of the version needs to be bumped.

So API-wise, it'd align with https://github.com/pypa/setuptools_scm#extending-setuptools_scm. Let's say the name could be setuptools_scm.get_bump_segment_position.
Then, the end-users could provide a custom implementation of the version segment to be bumped detection. It'd look something like this:

MAJOR_SEGMENT = 1
MINOR_SEGMENT = 2
MICRO_SEGMENT = 3

def get_bump_segment_position():  # dunno if it needs to access any context through args
    ... # detect what types of the Towncrier fragments are present on disk
    if <there's some breaking changes>:
        return MAJOR_SEGMENT
    if <it's a new feature>:
        return MINOR_SEGMENT
    if <it's misc/docs/internal>:
        return MICRO_SEGMENT
    return None  # delegate the auto-detection back to setuptools-scm

I think this design would provide enough flexibility to the end-users while not forcing them to revert to using the legacy setup.py or an in-tree PEP 517 backend wrapping setuptools, for example.

[RonnyPfannschmidt]

I believe we need a expansion of the parse concept, so that towncrier /Scriv integration can provide worktree details

[webknjaz]

I'm not sure these tools should only interact with parse directly...