FIX: guarantee MNE sample data is bundled into JupyterLite build

Two coordinated fixes for the FileNotFoundError on /drive/mne_data
that crashes every intro notebook when run in the CircleCI preview.

.circleci/config.yml:
  Add an explicit 'Ensure MNE sample data for JupyterLite' step
  immediately before 'make html'. The existing circleci_download.sh
  script only downloads sample data when the modified tutorial files
  reference it via a text-grep check, so any PR that touches only
  configuration files (like this one) would result in a cache miss
  leaving ~/mne_data/MNE-sample-data absent. Without that directory
  conf.py cannot copy the required files into jupyterlite_contents/,
  /drive/mne_data never exists in the Pyodide virtual filesystem, and
  mne.datasets.sample.data_path() throws FileNotFoundError on the
  first meaningful cell of every tutorial notebook. The new step calls
  mne.datasets.sample.data_path(update_path=True) unconditionally,
  downloading the dataset if the cache is cold and skipping silently
  if it is already present.

doc/conf.py:
  Always create the jupyterlite_contents/mne_data/MNE-sample-data
  destination directory unconditionally (dst_sample_data.mkdir) before
  the copy loop runs, so /drive/mne_data is present in the Pyodide
  kernel's Emscripten virtual filesystem even if no files were copied.
  Also drop the 'not d.exists()' guard on individual file copies so
  each incremental Sphinx build refreshes the bundled data files from
  the current state of ~/mne_data/MNE-sample-data rather than skipping
  files that were already copied from a previous build run.

Author: natinew77-creator

.circleci/config.yml

@@ -249,6 +249,16 @@ jobs:
               cp junit-results.xml doc/_build/test-results/test-doc/junit.xml;
               cp coverage.xml doc/_build/test-results/test-doc/coverage.xml;
             fi;
+      # Ensure the MNE sample dataset is on disk so conf.py can copy the
+      # required subset into jupyterlite_contents/ for the JupyterLite build.
+      # circleci_download.sh only fetches sample data when the changed files
+      # reference it, so a cache miss on a PR that touches only doc/conf.py
+      # would leave ~/mne_data/MNE-sample-data absent and the notebooks would
+      # fail at runtime with FileNotFoundError on /drive/mne_data.
+      - run:
+          name: Ensure MNE sample data for JupyterLite
+          command: |
+            python -c "import mne; mne.datasets.sample.data_path(update_path=True)"
       # Build docs
       - run:
           name: make html

doc/conf.py

@@ -479,14 +479,17 @@
 jupyterlite_contents = ["jupyterlite_contents"]
 jupyterlite_bind_ipynb_suffix = False
 
-# Automatically inject the required subset of MNE-sample-data into JupyterLite
+# Automatically inject the required subset of MNE-sample-data into JupyterLite.
+# The destination directory is always created so /drive/mne_data is present in
+# the Pyodide kernel's virtual filesystem even when no files have been copied.
 src_sample_data = Path(os.path.expanduser("~/mne_data/MNE-sample-data"))
 dst_sample_data = (
     Path(os.path.abspath(os.path.dirname(__file__)))
     / "jupyterlite_contents"
     / "mne_data"
     / "MNE-sample-data"
 )
+dst_sample_data.mkdir(parents=True, exist_ok=True)
 if src_sample_data.exists():
     required_files = [
         "version.txt",
@@ -506,10 +509,11 @@
     for req in required_files:
         s = src_sample_data / req
         d = dst_sample_data / req
-        if s.exists() and not d.exists():
+        if s.exists():
             d.parent.mkdir(parents=True, exist_ok=True)
             shutil.copy2(s, d)
 
+
 # Also inject SSVEP and EEGLAB testing datasets for JupyterLite
 mne_data_base = Path(os.path.expanduser("~/mne_data"))
 lite_data_base = (