Restrict Qt6 CI to Ubuntu 20.04.

Also, PyGObjects built on different Ubuntus are incompatible, so the
cache should be keyed by matrix.os (which includes the version number),
not runner.os (which doesn't).

Author: anntzer

.github/workflows/tests.yml

@@ -95,6 +95,9 @@ jobs:
               texlive-luatex \
               texlive-xetex \
               ttf-wqy-zenhei
+            if [[ "${{ matrix.os }}" = ubuntu-20.04 ]]; then
+              sudo apt install -yy libopengl0
+            fi
             ;;
           macOS)
             brew install ccache
@@ -106,25 +109,25 @@ jobs:
         if: startsWith(runner.os, 'Linux')
         with:
           path: ~/.cache/pip
-          key: ${{ runner.os }}-py${{ matrix.python-version }}-pip-${{ hashFiles('requirements/*/*.txt') }}
+          key: ${{ matrix.os }}-py${{ matrix.python-version }}-pip-${{ hashFiles('requirements/*/*.txt') }}
           restore-keys: |
-            ${{ runner.os }}-py${{ matrix.python-version }}-pip-
+            ${{ matrix.os }}-py${{ matrix.python-version }}-pip-
       - name: Cache pip
         uses: actions/cache@v2
         if: startsWith(runner.os, 'macOS')
         with:
           path: ~/Library/Caches/pip
-          key: ${{ runner.os }}-py${{ matrix.python-version }}-pip-${{ hashFiles('requirements/*/*.txt') }}
+          key: ${{ matrix.os }}-py${{ matrix.python-version }}-pip-${{ hashFiles('requirements/*/*.txt') }}
           restore-keys: |
-            ${{ runner.os }}-py${{ matrix.python-version }}-pip-
+            ${{ matrix.os }}-py${{ matrix.python-version }}-pip-
       - name: Cache ccache
         uses: actions/cache@v2
         with:
           path: |
             ~/.ccache
-          key: ${{ runner.os }}-py${{ matrix.python-version }}-ccache-${{ hashFiles('src/*') }}
+          key: ${{ matrix.os }}-py${{ matrix.python-version }}-ccache-${{ hashFiles('src/*') }}
           restore-keys: |
-            ${{ runner.os }}-py${{ matrix.python-version }}-ccache-
+            ${{ matrix.os }}-py${{ matrix.python-version }}-ccache-
       - name: Cache Matplotlib
         uses: actions/cache@v2
         with:
@@ -171,25 +174,28 @@ jobs:
             # Sept 2020) for either pyqt5 (there are only wheels for 10.13+) or
             # pyside2 (the latest version (5.13.2) with 10.12 wheels has a
             # fatal to us bug, it was fixed in 5.14.0 which has 10.13 wheels)
-             python -m pip install --upgrade pyqt5${{ matrix.pyqt5-ver }} &&
-               python -c 'import PyQt5.QtCore' &&
-               echo 'PyQt5 is available' ||
-               echo 'PyQt5 is not available'
-             python -m pip install --upgrade pyside2 &&
-               python -c 'import PySide2.QtCore' &&
-               echo 'PySide2 is available' ||
-               echo 'PySide2 is not available'
-             python -mpip install --upgrade pyqt6 &&
-               python -c 'import PyQt6.QtCore' &&
-               echo 'PyQt6 is available' ||
-               echo 'PyQt6 is not available'
-             python -mpip install --upgrade pyside6 &&
-               python -c 'import PySide6.QtCore' &&
-               echo 'PySide6 is available' ||
-               echo 'PySide6 is not available'
+            python -mpip install --upgrade pyqt5${{ matrix.pyqt5-ver }} &&
+              python -c 'import PyQt5.QtCore' &&
+              echo 'PyQt5 is available' ||
+              echo 'PyQt5 is not available'
+            python -mpip install --upgrade pyside2 &&
+              python -c 'import PySide2.QtCore' &&
+              echo 'PySide2 is available' ||
+              echo 'PySide2 is not available'
+            # Qt6 crashes on Github's ubuntu 18.04 runner.
+            if [[ "${{ matrix.os }}" = ubuntu-20.04 ]]; then
+              python -mpip install --upgrade pyqt6 &&
+                python -c 'import PyQt6.QtCore' &&
+                echo 'PyQt6 is available' ||
+                echo 'PyQt6 is not available'
+              python -mpip install --upgrade pyside6 &&
+                python -c 'import PySide6.QtCore' &&
+                echo 'PySide6 is available' ||
+                echo 'PySide6 is not available'
+            fi
           fi
-          python -m pip install --upgrade \
-            -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-$(lsb_release -r -s) \
+          python -mpip install --upgrade \
+            -f "https://extras.wxpython.org/wxPython4/extras/linux/gtk3/${{ matrix.os }}" \
             wxPython &&
             python -c 'import wx' &&
             echo 'wxPython is available' ||

lib/matplotlib/tests/test_sphinxext.py

@@ -18,6 +18,17 @@ def test_tinypages(tmpdir):
     shutil.copytree(Path(__file__).parent / 'tinypages', source_dir)
     html_dir = source_dir / '_build' / 'html'
     doctree_dir = source_dir / 'doctrees'
+    # Build the pages with warnings turned into errors
+    cmd = [sys.executable, '-msphinx', '-W', '-b', 'html',
+           '-d', str(doctree_dir),
+           str(Path(__file__).parent / 'tinypages'), str(html_dir)]
+    # On CI, gcov emits warnings (due to agg headers being included with the
+    # same name in multiple extension modules -- but we don't care about their
+    # coverage anyways); hide them using GCOV_ERROR_FILE.
+    proc = Popen(
+        cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
+        env={**os.environ, "MPLBACKEND": "", "GCOV_ERROR_FILE": os.devnull})
+    out, err = proc.communicate()
 
     # Build the pages with warnings turned into errors
     build_sphinx_html(source_dir, doctree_dir, html_dir)