No hash library appears to be generated with --mpl-generate-summary and xdist

[Cadair]

I'm not 100% sure where this is coming from but it seems that sunpy PRs are no longer generating hash libraries we can download to update the hashes.

Is this something which stops working with xdist? @ConorMacBride

[ConorMacBride]

Just had a look into this. The result hashes are only missing when the hash library is set with the kwarg (@pytest.mark.mpl_image_compare(hash_library=hash_library_file)).

The xdist controller process handles the generation of summaries, however it doesn't have access to the test-specific kwarg hash library value so doesn't know what to name the result hash library. (This isn't an issue when using the CLI and INI options as the xdist controller has access to these.)

The easiest fix would be to use a default name such as hashes.json for the result hash library when using xdist and a kwarg hash library setting. What do you think?

(It doesn't have tests, but technically you can use the kwarg to specify a different baseline hash file for each test, so it's probably best to just use a default name instead of trying to get the kwarg value from a worker.)

[Cadair]

Thanks for looking into this!A default name would be fine for the sunpy case.

The reason we set that keyword is because we need a runtime way of setting the name, as it has versions of things in (like mpl and freetype). Can you think of a better way to set the name globally at runtime? Can we hook into the config rather than passing a kwarg?