fix(ci): pass flake.lock via outputs, only push after successful build

Author: djgoku

.github/workflows/emacs-overlay.yml

@@ -16,6 +16,7 @@ jobs:
     if: github.repository_owner == 'djgoku'
     outputs:
       changes_exist: ${{ steps.update.outputs.changes_exist }}
+      flake_lock: ${{ steps.update.outputs.flake_lock }}
     steps:
       - uses: actions/checkout@v6
         with:
@@ -32,17 +33,16 @@ jobs:
         id: update
         working-directory: emacs-overlay
         run: |
-          echo "=== Running mise update task ==="
-          OUTPUT=$(mise run update 2>&1) || true
-          echo "=== Task output ==="
-          echo "$OUTPUT"
-          echo "=== Checking for changes ==="
-          if echo "$OUTPUT" | grep -q "CHANGES_EXIST=true"; then
-            echo "Changes detected, build will be triggered"
-            echo "changes_exist=true" >> $GITHUB_OUTPUT
-          else
+          mise run update
+          if git diff --quiet flake.lock; then
             echo "No changes detected, build will be skipped"
             echo "changes_exist=false" >> $GITHUB_OUTPUT
+          else
+            echo "Changes detected, build will be triggered"
+            echo "changes_exist=true" >> $GITHUB_OUTPUT
+            echo "flake_lock<<EOF" >> $GITHUB_OUTPUT
+            cat flake.lock >> $GITHUB_OUTPUT
+            echo "EOF" >> $GITHUB_OUTPUT
           fi
   build:
     if: needs.update.outputs.changes_exist == 'true'
@@ -63,6 +63,9 @@ jobs:
           install: false
       - name: Install mise nix plugin
         run: mise plugins install nix https://github.com/jbadeau/mise-nix.git
+      - name: Write updated flake.lock
+        working-directory: emacs-overlay
+        run: echo '${{ needs.update.outputs.flake_lock }}' > flake.lock
       - name: Build Emacs
         working-directory: emacs-overlay
         run: mise run build
@@ -74,5 +77,14 @@ jobs:
       - uses: actions/checkout@v6
         with:
           ref: ${{ inputs.build-branch || 'build-emacs-overlay' }}
-      - name: Push updated flake.lock
-        run: git push
+      - name: Write updated flake.lock
+        working-directory: emacs-overlay
+        run: echo '${{ needs.update.outputs.flake_lock }}' > flake.lock
+      - name: Commit and push
+        working-directory: emacs-overlay
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add flake.lock
+          git commit -m "Updated flake inputs for latest emacs-overlay"
+          git push