improvements to the inference of the version from the tag

[jinxidoru]

The current implementation of cpm_get_version_from_git_tag() has some odd behavior in scenarios that do not perfectly match the expected v#.#.# format. This change attempts to better clarify and slightly expand the functionality. The motivating event for this change was when I attempted to bring in avro, which uses a tag format that looks like this: "release-1.12.0". The current implementation was not properly parsing out the 1.12.0 version.

This change creates two scenarios. In the first, we check for the appearance of "v" followed by a number anywhere in the tag. If that is encountered, then we treat that number and any number or dot following it as the version number. This could be made more restrictive by requiring that a dot also appear, though this limitation does not exist in the current version and could break current situations. This case is meant to mimic the current approach.

The second case is less restrictive and simply looks for numbers followed by a dot and more numbers anywhere in the string. This will handle any case where the version number appears mid string. I think the current regex was meant to handle this scenario, but it was not actually working correctly.

Let me know what your thoughts are. I'm happy to walk through some of the issues I was encountering as I diagnosed the problem.

[TheLartians]

Hey thanks for raising the issue and the potential fix! One thing I slightly worry about is false positives coming from unrelated tags that shouldn't imply a version. I don't believe it's a big deal as the version is mainly used for emitting a warning if a dependency wants a more recent one, but it would be good to work as expected for most cases.

I'm happy with moving forward with the suggested approach, could you add some test cases to test/unit/version_from_git_tag.cmake, checking both for common tag patterns that we want to support and making sure we avoid potential false positives as well e.g. from git hash like tags?