Add dynamic version for the python backend

[tdejager]

Add the ability to use dynamic versions with the python backends. This would require the backend to run python code, namely the metadata hook to get the dynamic version before rendering as this is required in the render. With this the correct metadata needs to be returned.

I think with #2947 we should also communicate if the backend supports this. But unsure as of yet.

[dhirschfeld]

The only use I have for the dynamic version is to inject the git describe information to provide an ordering and label the artifact with the sha it was built from for provenance.

I use hatch-vcs but, because the builtin version schemes aren't flexible enough, I have my own hook that uses the tag, distance and sha information to construct a post.dev version scheme according to PEP-440.

I think you could get pretty far by just allowing a format string with the tag, distance and sha information able to be interpolated. That way you wouldn't need to allow arbitrary code execution, at least in the common case.

[theavey]

I've been using poetry-dynamic-versioning (which uses a Python package called dunamai underneath).

I find it pretty useful and powerful to jinja-template the version I want within my pyproject.toml. Mine is a bit more complicated than I assume most will want (distinct version for local "dirty" builds, unreleased dev versions, post release versions, alpha versions, commits after alpha versions...), but maybe a simpler templateable dynamic version is a target to aim for.

Agree with @dhirschfeld that tag, distance, and hash are enough for most cases, though branch would be very nice as well IMO.

[tool.poetry-dynamic-versioning]
enable = true
vcs = "git"
pattern = "default-unprefixed"
format-jinja = """
    {%- set revision = revision | int -%}
    {%- if stage is not none -%}
        {%- if dirty -%}
            {{ serialize_pep440(
                base, stage=stage, revision=revision+distance, metadata=[commit, "dirty"]
            ) }}
        {%- else -%}
            {{ serialize_pep440(
                base, stage=stage, revision=revision+distance, metadata=[commit]
            ) }}
        {%- endif -%}
    {%- elif distance == 0 -%}
        {{ serialize_pep440(base) }}
    {%- elif dirty -%}
        {{ serialize_pep440(
            bump_version(base), dev=distance, metadata=[commit, "dirty"]
        ) }}
    {%- elif branch == "master" -%}
        {{ serialize_pep440(base, post=distance, metadata=[commit]) }}
    {%- else -%}
        {{ serialize_pep440(bump_version(base), dev=distance, metadata=[commit]) }}
    {%- endif -%}
"""