Fix Windows bug with local time in BIDS datasets and add tests

doc/whats_new.rst

@@ -56,6 +56,7 @@ Detailed list of changes
 
 - Fixed a bug that modified the name and help message of some of the available commands, by `Alex Lopez Marquez`_ (:gh:`1441`)
 - Updated MEG/iEEG writers to satisfy the stricter checks in the latest BIDS validator releases: BTi/4D run folders now retain their ``.pdf`` suffix (falling back to the legacy naming when an older validator is detected), KIT marker files encode the run via the ``acq`` entity instead of ``run``, datasets lacking iEEG montages receive placeholder ``electrodes.tsv``/``coordsystem.json`` files, and the ``AssociatedEmptyRoom`` entry stores dataset-relative paths  by `Bruno Aristimunha`_ (:gh:`1449`)
+- Fixed a bug in :func:`mne_bids.read_raw_bids` that caused it to fail when reading BIDS datasets where the acquisition time was specified in local time rather than UTC only in Windows, by `Bruno Aristimunha`_ (:gh:`1452`)
 
 ⚕️ Code health
 ^^^^^^^^^^^^^^

mne_bids/read.py

@@ -420,6 +420,10 @@ def _handle_scans_reading(scans_fname, raw, bids_path):
             acq_time = acq_time.replace(tzinfo=timezone.utc)
         else:
             # Convert time offset to UTC
+            if acq_time.tzinfo is None:
+                # Windows needs an explicit local tz for naive, pre-epoch times.
+                local_tz = datetime.now().astimezone().tzinfo or timezone.utc
+                acq_time = acq_time.replace(tzinfo=local_tz)
             acq_time = acq_time.astimezone(timezone.utc)
 
         logger.debug(f"Loaded {scans_fname} scans file to set acq_time as {acq_time}.")

mne_bids/tests/test_read.py

@@ -834,6 +834,21 @@ def test_handle_scans_reading(tmp_path):
         new_acq_time = datetime.strptime(new_acq_time_str, date_format)
         assert raw_03.info["meas_date"] == new_acq_time.astimezone(timezone.utc)
 
+    # Regression for naive, pre-epoch acquisition times (Windows bug GH-1399)
+    pre_epoch_str = "1950-06-15T13:45:30"
+    scans_tsv["acq_time"][0] = pre_epoch_str
+    _to_tsv(scans_tsv, scans_path)
+
+    raw_pre_epoch = read_raw_bids(bids_path)
+    pre_epoch_naive = datetime.strptime(pre_epoch_str, "%Y-%m-%dT%H:%M:%S")
+    local_tz = datetime.now().astimezone().tzinfo or timezone.utc
+    expected_pre_epoch = pre_epoch_naive.replace(tzinfo=local_tz).astimezone(
+        timezone.utc
+    )
+    assert raw_pre_epoch.info["meas_date"] == expected_pre_epoch
+    if raw_pre_epoch.annotations.orig_time is not None:
+        assert raw_pre_epoch.annotations.orig_time == expected_pre_epoch
+
 
 @pytest.mark.filterwarnings(warning_str["channel_unit_changed"])
 def test_handle_scans_reading_brainvision(tmp_path):