get_version(version_scheme='python-simplfied-semver') fails when considering a semantic version tag with pre-release or build IDs

[jasongraham]

Steps to reproduce:

• setuptools-scm-4.1.2
• Python 3.8
• Create git repository with arbitrary contents.
• Tag your most recent commit with a release that specifies a semantic version and includes a pre-release or build identifier. I used 1.0.0-foo

>>> import setuptools_scm as scm
>>> scm.get_version(version_scheme='python-simplified-semver')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../site-packages/setuptools_scm/__init__.py", line 144, in get_version
    return _get_version(config)
  File .../site-packages/setuptools_scm/__init__.py", line 151, in _get_version
    version_string = format_version(
  File ".../site-packages/setuptools_scm/version.py", line 345, in format_version
    main_version = version_scheme(version)
  File ".../site-packages/setuptools_scm/version.py", line 258, in simplified_semver_version
    return guess_next_simple_semver(version.tag, retain=SEMVER_LEN, increment=False)
  File ".../site-packages/setuptools_scm/version.py", line 246, in guess_next_simple_semver
    parts = [int(i) for i in str(version).split(".")[:retain]]
  File ".../site-packages/setuptools_scm/version.py", line 246, in <listcomp>
    parts = [int(i) for i in str(version).split(".")[:retain]]
ValueError: invalid literal for int() with base 10: '0-foo'

I had expected in this case that the tag name would be used as the version (1.0.0-foo).

A similar exception gets raised looking back toward that tag in a later added commit.

...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../site-packages/setuptools_scm/__init__.py", line 144, in get_version
    return _get_version(config)
  File ".../site-packages/setuptools_scm/__init__.py", line 151, in _get_version
    version_string = format_version(
  File ".../site-packages/setuptools_scm/version.py", line 345, in format_version
    main_version = version_scheme(version)
  File ".../site-packages/setuptools_scm/version.py", line 265, in simplified_semver_version
    return version.format_next_version(
  File ".../site-packages/setuptools_scm/version.py", line 179, in format_next_version
    guessed = guess_next(self.tag, **kw)
  File ".../site-packages/setuptools_scm/version.py", line 246, in guess_next_simple_semver
    parts = [int(i) for i in str(version).split(".")[:retain]]
  File ".../site-packages/setuptools_scm/version.py", line 246, in <listcomp>
    parts = [int(i) for i in str(version).split(".")[:retain]]
ValueError: invalid literal for int() with base 10: '0-foo'

In this case, I would expect that the created version would either something like 1.0.0-devN... or more ideally 1.0.0-foo.devN.

Looking at the code listed in the traceback, it looks like the tool would also choke on any build IDs that were included, though I expect creating a tag with that information would be weird.

I do think that tags with pre-release IDs on them are common enough that I would expect these to work.

[RonnyPfannschmidt]

In that case we should throw a better error, the simplified semver only handles numbers

Python versions don't directly support semver data, one is supposed to add that kinda data in local tags (where setuptools _scm could have some better tooling)