MRG: Don't create directories when accessing BIDSPath.fpath

[hoechenberger]

Don't unexpectedly create directories when users don't actually intend to alter the BIDS dataset.

The problem was reported by multiple users on the forum:
https://mne.discourse.group/t/bidspath-creating-new-directory-when-specified-dir-doesnt-exist/6928

And it's also something that has actually bothered me for years.

I simply removed an .mkdir() call, which seemed unnecessary anyway.

Fails on main, passes on this branch:

from pathlib import Path
import tempfile
from mne_bids import BIDSPath, print_dir_tree


with tempfile.TemporaryDirectory() as bids_root:
    bids_root = Path(bids_root)
    bp = BIDSPath(subject='01', datatype='eeg', root=bids_root)
    bp.fpath  # accessing .fpath is required for this regression test
    assert not (bids_root / 'sub-01').exists()

Merge checklist

Maintainer, please confirm the following before merging.
If applicable:

• All comments are resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• New contributors have been added to CITATION.cff
• PR description includes phrase "closes <#issue-number>"

[codecov]

Codecov Report

Merging #1139 (19e751a) into main (96a4532) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1139   +/-   ##
=======================================
  Coverage   95.28%   95.28%           
=======================================
  Files          40       40           
  Lines        8695     8699    +4     
=======================================
+ Hits         8285     8289    +4     
  Misses        410      410           

Impacted Files	Coverage Δ
mne_bids/path.py	97.70% <100.00%> (ø)
mne_bids/tests/test_path.py	99.84% <100.00%> (+<0.01%)	⬆️

[sappelhoff]

I agree that it's cleaner to not create directories here and there. I just wonder why we had it in the first place.

[hoechenberger]

I agree that it's cleaner to not create directories here and there. I just wonder why we had it in the first place.

Maybe it was just a leftover from some old refactoring. I was very surprised to see the entire test suite pass after removing it. 😅