ci: automate image builds based on freeze file changes (#257)

.github/workflows/build.yaml

@@ -1,6 +1,13 @@
 name: Image Builder
 
 on:
+  push:
+    branches:
+      - main
+    paths:
+      - alpine/freeze/**
+      - static/freeze/**
+      - ubuntu/freeze/**
   workflow_dispatch:
     inputs:
       pandoc_version:
@@ -18,11 +25,50 @@ on:
           - static
 
 jobs:
-  # Build images and store them as tar archive
-  core:
-    name: minimal and core
+  prepare:
     runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - id: set-matrix
+        run: |
+          if [[ "${{ github.event_name }}" == "workflow_dispatch" ]]; then
+            echo "matrix={\"include\":[{\"stack\":\"${{ inputs.base_system }}\",\"version\":\"${{ inputs.pandoc_version }}\"}]}" >> $GITHUB_OUTPUT
+          else
+            CHANGED_FILES=$(git diff --name-only ${{ github.event.before }} ${{ github.event.after }})
+            MATRIX="{\"include\":["
+            FIRST=true
+
+            for STACK in alpine ubuntu static; do
+              if echo "$CHANGED_FILES" | grep -q "^$STACK/"; then
+                FREEZE_FILE=$(echo "$CHANGED_FILES" | grep "^$STACK/.*\.project\.freeze$" | head -1)
+                if [ -n "$FREEZE_FILE" ]; then
+                  VERSION=$(basename "$FREEZE_FILE" | sed -E 's/pandoc-(.*)\.project\.freeze/\1/')
+                  if [ "$FIRST" = true ]; then
+                    FIRST=false
+                  else
+                    MATRIX="${MATRIX},"
+                  fi
+                  MATRIX="${MATRIX}{\"stack\":\"{$STACK:-alpine}\",\"version\":\"${VERSION:-main}\"}"
+                fi
+              fi
+            done
+
+            MATRIX="${MATRIX}]}"
+            echo "matrix=$MATRIX" >> $GITHUB_OUTPUT
+          fi
 
+  core:
+    name: minimal and core (${{ matrix.stack }})
+    needs: prepare
+    runs-on: ubuntu-latest
+    strategy:
+      matrix: ${{ fromJSON(needs.prepare.outputs.matrix) }}
+      fail-fast: false
+
     steps:
       - uses: actions/checkout@v4
 
@@ -51,49 +97,58 @@ jobs:
         uses: ./.github/actions/build
         with:
           image_type: minimal
-          base_system: ${{ inputs.base_system }}
-          pandoc_version: ${{ inputs.pandoc_version }}
-          dockerfile: ${{ inputs.base_system }}/Dockerfile
-          target: ${{ inputs.base_system }}-minimal
+          base_system: ${{ matrix.stack }}
+          pandoc_version: ${{ matrix.version }}
+          dockerfile: ${{ matrix.stack }}/Dockerfile
+          target: ${{ matrix.stack }}-minimal
 
       - name: core
         uses: ./.github/actions/build
-        if: ${{ inputs.base_system != 'static' }}
+        if: ${{ matrix.stack != 'static' }}
         with:
           image_type: core
-          base_system: ${{ inputs.base_system }}
-          pandoc_version: ${{ inputs.pandoc_version }}
-          dockerfile: ${{ inputs.base_system }}/Dockerfile
-          target: ${{ inputs.base_system }}-core
+          base_system: ${{ matrix.stack }}
+          pandoc_version: ${{ matrix.version }}
+          dockerfile: ${{ matrix.stack }}/Dockerfile
+          target: ${{ matrix.stack }}-core
 
   typst:
-    name: Typst
-    if: ${{ inputs.base_system != 'static' }}
-    needs: core
+    name: Typst (${{ matrix.stack }})
+    if: ${{ matrix.stack != 'static' }}
+    needs: [prepare, core]
+    strategy:
+      matrix: ${{ fromJSON(needs.prepare.outputs.matrix) }}
+      fail-fast: false
     uses: ./.github/workflows/addon.yaml
     secrets: inherit
     with:
       addon: typst
-      base_system: ${{ inputs.base_system }}
-      pandoc_version: ${{ inputs.pandoc_version }}
+      base_system: ${{ matrix.stack }}
+      pandoc_version: ${{ matrix.version }}
 
   latex:
-    name: LaTeX
-    if: ${{ inputs.base_system != 'static' }}
-    needs: core
+    name: LaTeX (${{ matrix.stack }})
+    if: ${{ matrix.stack != 'static' }}
+    needs: [prepare, core]
+    strategy:
+      matrix: ${{ fromJSON(needs.prepare.outputs.matrix) }}
+      fail-fast: false
     uses: ./.github/workflows/addon.yaml
     secrets: inherit
     with:
       addon: latex
-      base_system: ${{ inputs.base_system }}
-      pandoc_version: ${{ inputs.pandoc_version }}
+      base_system: ${{ matrix.stack }}
+      pandoc_version: ${{ matrix.version }}
 
   extra:
-    name: Extra
-    needs: latex
+    name: Extra (${{ matrix.stack }})
+    needs: [prepare, latex]
+    strategy:
+      matrix: ${{ fromJSON(needs.prepare.outputs.matrix) }}
+      fail-fast: false
     uses: ./.github/workflows/addon.yaml
     secrets: inherit
     with:
       addon: extra
-      base_system: ${{ inputs.base_system }}
-      pandoc_version: ${{ inputs.pandoc_version }}
+      base_system: ${{ matrix.stack }}
+      pandoc_version: ${{ matrix.version }}