Use log level info when ignoring packages due to environment markers

[edmorley]

The use of environment markers implies that the user expects the packages to not be installed in some cases (eg depending on version of Python), so the log output shouldn't be classed as a warning, particularly since this results in it being sent to stderr rather than stdout.

Fixes #4876.

[edmorley]

Is there someone who has a spare moment to review this? :-)

[pradyunsg]

Sounds and looks fine to me.

[GabrielC101]

I'm a little concerned about this.

If the user is specifying an extra, via pip install package_name[extra_name], it's because the user expects extra_name to be available.

An unavailable extra is an error.

Can this be handled in a way that treats failed extra evaluations as errors, but other evaluations as info events?

[GabrielC101]

Never mind. If the user requests a non-existent extra, the logging takes place at https://github.com/pypa/pip/blob/master/src/pip/_internal/resolve.py#L295.

[edmorley]

I've rebased this on master.
It has one review approval - is another required, or can this be merged? :-)

[pradyunsg]

I'd like one more.

[pfmoore]

I'm fine with the implementation of the change, but I'm not completely convinced by the argument for why it's needed - It feels correct to me that if we ignore a requirement, that's a warning, not an informational message. But the distinction between warn and info is so subtle in practice, that I don't care a whole lot.

So @pradyunsg if you feel OK with switching the level of this message, I'm happy to be your second approval that it's implemented correctly. If you're after approval that the change of level is OK, then I'd say "don't know, but I doubt it's a big deal either way".

[edmorley]

Hi! Thank you for taking a look :-)

Can you think of some example use-cases where skipping a requirement really is something of concern that needs a warning on stderr? #4876 has a use-case for the reverse - and I'd suspect that's more common.

[pradyunsg]

(sorry for the terse statement before.)

@pfmoore I agree with everything you said.

I'm slightly more accepting of this change mostly because I'd prefer spewing less text into stderr for that reason I'm cool with doing a change in level here.

[edmorley]

Many thanks :-)

[lock]

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