Allow filtering tags when using SCM to determine the version

[mezuzza]

I've used PDM in a few monorepos. In each one, I need to build different projects which all have dynamic SCM versioning enabled. Each project has it's own versioning determined by git tags. e.g. project-a/0.1.1 and project-b/2.1.1. However, when using scm versioning, only the most recent of those tags will be used and only one project will derive a proper version number.

The workaround for git is to use a call based version and reuse most of the same machinery (see below for the workaround).

I don't know the equivalent for mercurial, but for git, we simply need to be able to provide an argument for the --match command line argument for git describe called here in pdm.

Would it be possible to provide a tag_filter key in the tool.pdm.version table which accepts a glob that is used for the --match parameter?

Workaround:

import subprocess

from pdm.backend.hooks.version.scm import (
    DEFAULT_TAG_REGEX,
    Config,
    VersionInfo,
    _git_parse_describe,
    format_version,
    tag_to_version,
)

_PACKAGE_PREFIX = "project-a/"


def get_version():
    branch = subprocess.run(
        ["git", "rev-parse", "--abbrev-ref", "HEAD"],
        capture_output=True,
        encoding="utf-8",
    )

    describe = subprocess.run(
        ["git", "describe", "--long", "--match", f"{_PACKAGE_PREFIX}*", "--dirty"],
        capture_output=True,
        encoding="utf-8",
    )

    tag, distance, node, dirty = _git_parse_describe(describe.stdout.strip())

    version = tag_to_version(Config(DEFAULT_TAG_REGEX), tag)

    return format_version(
        VersionInfo(
            version=version,
            distance=distance or None,
            dirty=dirty,
            node=node,
            branch=branch.stdout.strip(),
        )
    )

[frostming]

This requirement is reasonable and the solution is also very clear. Would you like to submit a PR?

[mezuzza]

I'll try to get to it this week, but no promises.

Do you happen to have any ideas on whether this is an issue for hg and if so how you might solve for it? I'll probably leave that as a TODO and let that happen in a separate PR.

[frostming]

There are two situations here:

1. If the current commit is associated with a tag, you need to check if it matches the pattern. hg does this through here:

   pdm-backend/src/pdm/backend/hooks/version/scm.py

   Line 285 in 74f7a61

   _, output, _ = _subprocess_call("hg id -i -b -t", root)

2. If not, it looks for its ancestors to find the nearest tag, and it accepts a regex pattern(the part after re: is a regex):

   pdm-backend/src/pdm/backend/hooks/version/scm.py

   Line 210 in 74f7a61

   "ancestors(.) and tag('re:\\.')",