semver.Version as default causing an error

[Linux13524]

Any instance of semver.Version set as default in an option will lead to an error when Click tries to show it in the help text.
The problem seems to be that Version allows comparison to strings, and Click, when building the help text, tries to check the default value against an empty string "", which cannot be parsed by semver.Version:

  File ".venv/lib/python3.12/site-packages/click/core.py", line 3091, in get_help_extra
    elif default_value == "":
         ^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/semver/version.py", line 52, in wrapper
    return operator(self, other)
           ^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/semver/version.py", line 467, in __eq__
    return self.compare(other) == 0
           ^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/semver/version.py", line 394, in compare
    other = cls.parse(other)
            ^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.12/site-packages/semver/version.py", line 644, in parse
    raise ValueError(f"{version} is not valid SemVer string")
ValueError:  is not valid SemVer string

This can be replicated with the following code by trying to print the help text:

Details

import click
from semver import Version


class SemverType(click.ParamType):
    name = "semver"

    def convert(self, value: str | Version, param: click.Parameter | None, ctx: click.Context | None) -> Version:
        if isinstance(value, Version):
            return value

        try:
            return Version.parse(value)
        except ValueError as e:
            raise self.fail(str(e), param, ctx) from e


@click.command()
@click.option(
    "--version",
    type=SemverType(),
    default=Version(1, 0, 0),
    show_default=True,
)
def cli(version: Version | None) -> None:
    print(version)


if __name__ == "__main__":
    cli()

By quickly inspecting the code, I'd say this could be fixed by checking whether default_value is actually a string before comparing it to "".

Environment:

• Python version: 3.12
• Click version: 8.3.1
• semver version: 3.0.4

[kdeldycke]

That's not unreasonable, as the empty string check is indeed a bit brutal. I am exploring the consequences at: #3299

[Linux13524]

Good to see there is already an open PR for it!