Proposed fix for #579

[ianpye]

Description

This PR proposes a simple fix to issue #579. Currently, the --pypi_to_conda_lookup_file flag does not work and produces an error whenever it is used, without checking the link first.

The removal of the following lines allows the flag to work as intended:

del self.pypi_lookup
del self.conda_lookup

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[maresb]

Thanks a lot @ianpye for taking the initiative on this!

I believe the proper fix is something more like:

        if self._mapping_url != value:
            self._mapping_url = value
            # Invalidate cache
            try:
                del self.pypi_lookup
            except AttributeError:
                pass
            try:
                del self.conda_lookup
            except AttributeError:
                pass

This feature desperately needs a test to prevent a similar regression in the future.

[ianpye]

Thanks @maresb for your input, I have changed my code to reflect those suggestions that you made.

[maresb]

Thanks @ianpye!

I made a quick attempt to write a test, but I didn't manage to get it to work properly yet. Do you have any ideas for a brief test that ensures we are using the specified mapping? I was thinking we could create a mapping URL that swaps some dependency, and then the test checks inside the generated lockfile for that substituted dependency.

[maresb]

Maybe I'm going the wrong way in my gist. I was thinking about constructing an example for pyproject.toml, but you're using only environment.yml, which is probably simpler.

[maresb]

The current test failure on macos is erroneous. See #591.

[ianpye]

@maresb What do you think about having 2 simple tests, one that uses the flag to point to the new mapping url that you provided and one that swaps the link to an invalid link. The 2nd test would check for failure and show that there is an attempt to connect to the link provided.