Use Pixi in macOS-intel CI

.github/workflows/tests.yml

@@ -54,7 +54,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     defaults:
       run:
-        shell: bash -el {0}
+        shell: bash -e {0}
     env:
       PYTHON_VERSION: '${{ matrix.python }}'
       MKL_NUM_THREADS: '1'
@@ -81,7 +81,7 @@ jobs:
             kind: mamba
           - os: macos-15-intel  # intel: Sequoia
             python: '3.13'
-            kind: mamba
+            kind: pixi
           - os: windows-latest
             python: '3.11'
             kind: mamba
@@ -123,6 +123,12 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
         if: startswith(matrix.kind, 'pip')
+      - uses: prefix-dev/setup-pixi@v0.9.4
+        with:
+          activate-environment: false
+          run-install: false
+          cache: false  # caching depends on existence of a pixi.lock file
+        if: matrix.kind == 'pixi'
       # Python (if conda)
       - name: Fixes for conda
         run: |
@@ -151,15 +157,47 @@ jobs:
           create-args: >-
             python=${{ env.PYTHON_VERSION }}
             -v
-        if: ${{ !startswith(matrix.kind, 'pip') }}
+          generate-run-shell: true
+          init-shell: none
+        if: ${{ !startswith(matrix.kind, 'pip') && matrix.kind != 'pixi' }}
         timeout-minutes: 20
+      - name: Create pixi.toml
+        if: matrix.kind == 'pixi'
+        # environment.yml specifies the same python version as macos-intel CI (3.13)
+        # but let's expliclty set the version, in case these ever diverge in the future?
+        run: |
+          pixi init --import environment.yml
+          pixi add "python==${{ matrix.python }}" --no-install
+      - name: Setup pixi environment
+        if: matrix.kind == 'pixi'
+        run: pixi install
+      # Now run setup-pixi again in order to activate the enviroment
+      - uses: prefix-dev/setup-pixi@v0.9.4
+        if: matrix.kind == 'pixi'
+        with:
+          run-install: true
+          activate-environment: true
+          cache: false
+      - name: Verify Environment
+        run: echo $PATH
+      - name: Debug Qt availability
+        if: matrix.kind == 'conda' || matrix.kind == 'mamba' || matrix.kind == 'old' || matrix.kind == 'minimal'
+        run: |
+          python -c "import sys; print(sys.executable)"
+          python -c "from importlib.metadata import version; print('pip version', version('pip'))"
+          python -c "from importlib import util; print('PySide6', util.find_spec('PySide6'))"
       - run: bash ./tools/github_actions_dependencies.sh
+        if: ${{ matrix.kind != 'pixi' && !startswith(matrix.kind, 'pip') && runner.os != 'Windows' }}
+        shell: micromamba-shell {0}
       - run: python ./tools/github_actions_check_old.py
         if: matrix.kind == 'old'
+        shell: micromamba-shell {0}
       # Minimal commands on Linux (macOS stalls)
       - run: bash ./tools/get_minimal_commands.sh
         if: startswith(matrix.os, 'ubuntu') && matrix.kind != 'minimal' && matrix.kind != 'old'
       - run: bash ./tools/github_actions_infos.sh
+        if: ${{ matrix.kind != 'pixi' && !startswith(matrix.kind, 'pip') && runner.os != 'Windows' }}
+        shell: micromamba-shell {0}
       # Check Qt
       - run: bash ./tools/check_qt_import.sh $MNE_QT_BACKEND
         if: env.MNE_QT_BACKEND != ''
@@ -172,7 +210,14 @@ jobs:
           key: ${{ env.TESTING_VERSION }}
           path: ~/mne_data
       - run: bash ./tools/github_actions_download.sh
+      - name: Debug interpreter + Qt
+        if: matrix.kind == 'pixi'
+        run: |
+          pixi run python -c "import sys; print(sys.executable)"
+          pixi run python -c "import PySide6; print(PySide6.__version__)"
       - run: bash ./tools/github_actions_test.sh  # for some reason on macOS we need to run "bash X" in order for a failed test run to show up
+        if: ${{ matrix.kind != 'pixi' && !startswith(matrix.kind, 'pip') && runner.os != 'Windows' }}
+        shell: micromamba-shell {0}
       - uses: codecov/codecov-action@v5
         with:
           token: ${{ secrets.CODECOV_TOKEN }}

tools/github_actions_dependencies.sh

@@ -25,6 +25,9 @@ if [ ! -z "$CONDA_ENV" ]; then
 		GROUP="test_extra"
 		EXTRAS="[hdf5]"
 	fi
+elif [[ "${MNE_CI_KIND}" == "pixi" ]]; then
+	GROUP="test_extra"
+	EXTRAS="[hdf5]"
 elif [[ "${MNE_CI_KIND}" == "pip" ]]; then
 	GROUP="test_extra"
 	EXTRAS="[full-pyside6]"

tools/github_actions_env_vars.sh

@@ -24,7 +24,14 @@ else  # conda-like
         echo "CONDA_ENV=tools/environment_minimal.yml" | tee -a $GITHUB_ENV
         echo "MNE_QT_BACKEND=PySide6" | tee -a $GITHUB_ENV
     else  # conda, mamba (use warning level for completeness)
-        echo "CONDA_ENV=environment.yml" | tee -a $GITHUB_ENV
+        # Pixi is treated as Conda-like (it uses environment.yaml) but it should not export
+        # CONDA_ENV because github_actions_dependencies.sh uses the existence of the
+        # CONDA_ENV environment variable to assume that the conda/mamba command is on
+        # PATH, which it is not for pixi jobs.
+        if [[ "$MNE_CI_KIND" != "pixi" ]]; then
+            echo "CONDA_ENV=environment.yml" | tee -a $GITHUB_ENV
+        fi
+
         echo "MNE_LOGGING_LEVEL=warning" | tee -a $GITHUB_ENV
         echo "MNE_QT_BACKEND=PySide6" | tee -a $GITHUB_ENV
         # TODO: Also need "|unreliable on GitHub Actions conda" on macOS, but omit for now to make sure the failure actually shows up