GH Actions/tests: run tests against multiple libxml versions

.github/workflows/test.yml

@@ -73,6 +73,17 @@ jobs:
           - php: '8.4'
             skip_tests: true
 
+          # The default libxml library on Ubuntu images is a little out of date.
+          # To safeguard support for the latest libxml we need to update the library on the fly.
+          # This only needs to be tested with one PHP version for each libxml minor to verify support.
+          # Testing against multiple PHP versions would not yield a difference in results.
+          - php: '8.0'
+            os: 'ubuntu-latest'
+            libxml_minor: '2.11'
+          - php: '8.3'
+            os: 'ubuntu-latest'
+            libxml_minor: '2.13'
+
           # Extra builds running only the unit tests with different PHP ini settings.
           - php: '5.5'
             os: 'ubuntu-latest'
@@ -82,7 +93,7 @@ jobs:
             custom_ini: true
 
     # yamllint disable-line rule:line-length
-    name: "PHP: ${{ matrix.php }} ${{ matrix.custom_ini && ' with custom ini settings' || '' }} (${{ matrix.os == 'ubuntu-latest' && 'Linux' || 'Win'  }})"
+    name: "PHP: ${{ matrix.php }} ${{ matrix.custom_ini && ' with custom ini settings' || '' }}${{ matrix.libxml_minor && format( ' with libxml {0}', matrix.libxml_minor ) || '' }} (${{ matrix.os == 'ubuntu-latest' && 'Linux' || 'Win'  }})"
 
     continue-on-error: ${{ matrix.php == '8.5' }}
 
@@ -93,6 +104,70 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: "libxml2: find the latest relevant tag"
+        if: ${{ matrix.libxml_minor }}
+        id: libxml_version
+        uses: oprypin/find-latest-tag@v1
+        with:
+          repository: GNOME/libxml2
+          releases-only: false  # The libxml2 repository doesn't use GitHub's "release" feature.
+          prefix: 'v${{ matrix.libxml_minor }}.' # Limit the result to the minor we're interested in.
+          sort-tags: true # Find the "greatest" version for that minor based on semver.
+
+      # To put it simply: we need to remove the 'v' prefix from the version number.
+      - name: "libxml2: parse the version to a patch version"
+        if: ${{ matrix.libxml_minor }}
+        id: libxml_patch_version
+        shell: bash
+        env:
+          TAG: ${{ steps.libxml_version.outputs.tag }}
+        run: echo "PATCH=$( echo "$TAG" | cut -b 2- )" >> "$GITHUB_OUTPUT"
+
+      - name: "libxml2: restore cache"
+        if: ${{ matrix.libxml_minor }}
+        id: libxml_cache_restore
+        uses: actions/cache/restore@v4
+        with:
+          path: "libxml2-${{ steps.libxml_patch_version.outputs.PATCH }}"
+          key: "${{ matrix.os }}-libxml-${{ matrix.libxml_minor }}-${{ steps.libxml_patch_version.outputs.PATCH }}"
+
+      # Updating the lists can fail intermittently, typically after Microsoft has released a new package.
+      # This should not be blocking for this job, so ignore any errors from this step.
+      # Ref: https://github.com/dotnet/core/issues/4167
+      - name: "libxml2: Update the available packages list"
+        if: ${{ matrix.libxml_minor && steps.libxml_cache_restore.outputs.cache-hit != 'true' }}
+        continue-on-error: true
+        run: sudo apt-get update
+
+      - name: "libxml2: Download and build package (linux only)"
+        if: ${{ matrix.libxml_minor && steps.libxml_cache_restore.outputs.cache-hit != 'true' }}
+        env:
+          PATCH: ${{ steps.libxml_patch_version.outputs.PATCH }}
+        run: |
+          sudo apt-get install -y wget build-essential
+          wget "https://download.gnome.org/sources/libxml2/${{ matrix.libxml_minor }}/libxml2-$PATCH.tar.xz"
+          tar -xf "libxml2-$PATCH.tar.xz"
+          cd "libxml2-$PATCH"
+          ./configure --prefix=/usr/local
+          make
+
+      - name: "libxml2: save cache"
+        if: ${{ matrix.libxml_minor && steps.libxml_cache_restore.outputs.cache-hit != 'true' }}
+        id: libxml_cache_save
+        uses: actions/cache/save@v4
+        with:
+          path: "libxml2-${{ steps.libxml_patch_version.outputs.PATCH }}"
+          key: ${{ steps.libxml_cache_restore.outputs.cache-primary-key }}
+
+      - name: "libxml2: Install package (linux only)"
+        if: ${{ matrix.libxml_minor }}
+        env:
+          PATCH: ${{ steps.libxml_patch_version.outputs.PATCH }}
+        run: |
+          cd "libxml2-$PATCH"
+          sudo make install
+          sudo ldconfig
+
       - name: Setup ini config
         id: set_ini
         shell: bash
@@ -115,6 +190,9 @@ jobs:
           coverage: none
           tools: cs2pr
 
+      - name: "DEBUG: show libxml loaded version (php)"
+        run: php -r 'echo "libxml loaded version = ", LIBXML_LOADED_VERSION, PHP_EOL;'
+
       # This action also handles the caching of the dependencies.
       - name: Set up node
         if: ${{ matrix.custom_ini == false }}