fix: prevent automation from producing broken PRs

- Preserve existing YARN_VERSION when running update.sh with -s flag
  instead of leaving template placeholder (0.0.0) in Dockerfiles
- Change build-automation.mjs to skip versions without musl builds
  instead of exiting early, preventing partial updates
- Add condition to workflow to skip PR creation when no versions
  were updated, preventing empty PR titles

Fixes issues seen in PRs #2341, #2347, #2350 where automation produced
Dockerfiles with YARN_VERSION=0.0.0 and/or empty PR titles.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: PeterDaveHello

.github/workflows/automatic-updates.yml

@@ -25,6 +25,7 @@ jobs:
 
       - name: Create update PR
         id: cpr
+        if: steps.updt.outputs.result != ''
         uses: peter-evans/create-pull-request@98357b18bf14b5342f975ff684046ec3b2a07725 # v8.0.0
         with:
           token: ${{ secrets.GH_API_TOKEN }}

build-automation.mjs

@@ -93,10 +93,15 @@ export default async function(github) {
         console.log(stdout);
         updatedVersions.push(newVersion.fullVersion);
       } else {
-        console.log(`There's no musl build for version ${newVersion.fullVersion} yet.`);
-        process.exit(0);
+        console.log(`Skipping version ${newVersion.fullVersion} - no musl build available yet.`);
       }
     }
+
+    if (updatedVersions.length === 0) {
+      console.log("No versions with musl builds were updated.");
+      process.exit(0);
+    }
+
     const { stdout } = (await exec(`git diff`));
     console.log(stdout);
 

update.sh

@@ -170,6 +170,12 @@ function update_node_version() {
     else
       if [ "${SKIP}" != true ]; then
         sed -Ei -e 's/^(ENV YARN_VERSION)=.*/\1='"${yarnVersion}"'/' "${dockerfile}-tmp"
+      else
+        # Preserve existing YARN_VERSION from current Dockerfile when SKIP=true
+        existingYarnVersion=$(sed -n 's/^ENV YARN_VERSION=//p' "${dockerfile}")
+        if [ -n "${existingYarnVersion}" ]; then
+          sed -Ei -e 's/^(ENV YARN_VERSION)=.*/\1='"${existingYarnVersion}"'/' "${dockerfile}-tmp"
+        fi
       fi
       echo "${dockerfile} updated!"
     fi