Only run the image builds if we are doing Linux Python builds

Author: zanieb

.github/workflows/linux.yml

@@ -46,15 +46,11 @@ jobs:
           path: target/release/pythonbuild
 
   image:
+    needs:
+      - generate-matrix
     strategy:
+      matrix: ${{ fromJson(needs.generate-matrix.outputs.image_matrix) }}
       fail-fast: false
-      matrix:
-        image:
-          - build
-          - build.cross
-          - gcc
-          - xcb
-          - xcb.cross
     runs-on: depot-ubuntu-22.04
     permissions:
       packages: write
@@ -121,7 +117,7 @@ jobs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
       - uses: actions/checkout@v4
-      
+
       - name: Set up Python
         uses: astral-sh/setup-uv@v4
 
@@ -131,22 +127,52 @@ jobs:
           # Convert GitHub labels array to comma-separated string
           LABELS=$(echo '${{ toJson(github.event.pull_request.labels.*.name) }}' | jq -r 'join(",")')
           echo "labels=$LABELS" >> $GITHUB_OUTPUT
-          
-      - name: Generate build matrix
+
+      - name: Generate matrix
         id: set-matrix
         run: |
-          uv run ci-matrix.py --platform linux --labels "${{ steps.get-labels.outputs.labels }}" > matrix.json && echo "matrix=$(cat matrix.json)" >> $GITHUB_OUTPUT
-          # Display the matrix for debugging too
-          cat matrix.json | jq
-        
+          # Generate the build matrix
+          uv run ci-matrix.py --platform linux --labels "${{ steps.get-labels.outputs.labels }}" > build_matrix.json
+
+          # Display the build matrix for debugging
+          echo "Build matrix:"
+          cat build_matrix.json | jq
+
+          # Check if build matrix is empty and generate image matrix accordingly
+          if jq -e '.include | length > 0' build_matrix.json > /dev/null; then
+            # Build matrix has entries, generate the image matrix
+            cat > image_matrix.json << EOL
+            {
+              "include": [
+                {"image": "build"},
+                {"image": "build.cross"},
+                {"image": "gcc"},
+                {"image": "xcb"},
+                {"image": "xcb.cross"}
+              ]
+            }
+            EOL
+          else
+            # Build matrix is empty, create empty image matrix
+            jq -n '{"include": []}' > image_matrix.json
+          fi
+
+          # Set both matrices as outputs
+          echo "build_matrix=$(cat build_matrix.json)" >> $GITHUB_OUTPUT
+          echo "image_matrix=$(jq -c '.' image_matrix.json)" >> $GITHUB_OUTPUT
+
+          # Display the image matrix for debugging
+          echo "Image matrix:"
+          cat image_matrix.json | jq
+
   build:
     needs:
       - generate-matrix
       - pythonbuild
       - image
     runs-on: depot-ubuntu-22.04
     strategy:
-      matrix: ${{ fromJson(needs.generate-matrix.outputs.matrix) }}
+      matrix: ${{ fromJson(needs.generate-matrix.outputs.build_matrix) }}
       fail-fast: false
     name: ${{ matrix.target_triple }} / ${{ matrix.python }} / ${{ matrix.build_options }}
     steps: