Add --favor-paths rez-env flag

[ColinKennedy]

Closes: #1263

Added rez-env cli option, --favor-paths

• If not provided, does nothing
• If provided and 1+ path specified, --favor-paths /foo:/bar
  • All packages found within /foo are preferred over packages found in /bar
  • All packages found in /bar are preferred over packages found within packages_path
• If provided but no paths specified, --favor-paths, [config.local_packages_path] is used. All other logic applies.
• In all cases, the usual package path rules still apply. e.g. any path provided in --favor-paths must be in packages_path or it won't be used during ordering

Miscellaneous

Introduced SplitPaths to show an alternative way we can be parsing our arguments. If you like that approach, I can add it to --paths as well, which is currently being described in setup_parser but then parsed again, in env.py command.

Question To Reviewers

I was thinking of also including a new rez.config.Config option for favor paths, so that people can set it via environment variable as well. I can think of some situations where this would be really desirable. Would that be okay to add?

What's not in this PR, currently

And now I recall - the problem we ran into when discussing this ages ago, is that orderers can't be stacked. So that could interfere with orderers already in place.

In the original ticket thread, #1263 (comment), @nerdvegas mentions that we may need a kind of "stacked orderer". However I didn't encounter any limitations in practice. ResolvedContext takes a list of package orderers so it should be fine. However please let me know if not and I'll make necessary adjustments.

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[diegogarciahuerta]

Hi @ColinKennedy , thanks for this PR, super useful!

We have been testing it in Windows and found one issue that I think should be easy to resolve.

It looks like Rez implements a canonical_path function, that amongst other things, converts the package locations to lowercase for case insensitive filesystems:

rez/src/rezplugins/package_repository/filesystem.py

Line 500 in 71f2f61

location = canonical_path(location, platform_)

canonical_path definition:

rez/src/rez/utils/filesystem.py

Line 528 in 71f2f61

if not platform.has_case_sensitive_filesystem:

In FavorPathsOrder you are checking if the package location is in the list of favor paths:
https://github.com/AcademySoftwareFoundation/rez/pull/1305/files#diff-772d1d5249a49e66b7497839f3f80ddb367c98ee0c880a8a3b2edf421ae817feR174

this comparison should be done with canonical_path in mind otherwise the check most likely always fail in Windows. ie. windows drive letters tend to be uppercase.

To solve it there are a couple of obvious options,

• either in the __init__ of the package ordered,

from rez.utils.filesystem import canonical_path

...

self._paths = [canonical_path(path) for path in paths]

or later on in the compoarison:

from rez.utils.filesystem import canonical_path

...
    def reorder(self, iterable, key=None):
...
        buckets = collections.OrderedDict([(canonical_path(path), []) for path in self._paths])

Hope this helps, I've tested both with our Windows setup and they work as expected.