`build_path` chooses the first pattern that matches, even when a better match exists

It looks like BIDSLayout.build_path() goes with the first path pattern it finds for which all required entities are given. I ran into a situation where this was blocking access to a better pattern later in the list. A minimal example:

from bids.layout import BIDSLayout
data=BIDSLayout('/path/to/my/BIDS/data')
entities = {'subject':'001', 
    'suffix':'T1w',
    'extension':'.nii.gz',
    'space':'MNI' }
patterns = ['sub-{subject}[/ses-{session}]/anat/sub-{subject}[_ses-{session}][_acq-{acquisition}][_ce-{ceagent}][_rec-{reconstruction}]_{suffix<T1w|T2w|T1rho|T1map|T2map|T2star|FLAIR|FLASH|PDmap|PD|PDT2|inplaneT[12]|angio>}.{extension<nii|nii.gz|json>|nii.gz}',
            'sub-{subject}[/ses-{session}]/anat/sub-{subject}[_ses-{session}][_acq-{acquisition}][_ce-{ceagent}][_rec-{reconstruction}][_space-{space}][_desc-{desc}]_{suffix<T1w|T2w|T1rho|T1map|T2map|T2star|FLAIR|FLASH|PDmap|PD|PDT2|inplaneT[12]|angio>}.{extension<nii|nii.gz|json>|nii.gz}']
print(data.build_path(entities, patterns, validate=False))
print(data.build_path(entities, patterns[1:], validate=False))

outputs the following:

sub-001/anat/sub-001_T1w.nii.gz
sub-001/anat/sub-001_space-MNI_T1w.nii.gz

Including the first pattern causes the 2nd to never be reached, even though it is better: patterns[1] makes use of the ‘space’ entity which is absent in patterns[0]. Users can work around this by giving the exact patterns they want and no others, but it would be nice if pybids tried to find a pattern which matched all given entities, or failing that, as many as possible.

[effigies]

The idea is that if extension isn’t present, nii.gz would be the default.

[effigies]

Okay. Could be that the handling of defaults and/or choices needs fixing up. I haven’t looked into it very much at this point, but it definitely seems like something that would be easy to get wrong. We have an open issue for really stress testing the path patterns: #478.