workflows: improve generate dockerfile workflow

- Run under perl:devel container
- Run only for changes on selected paths
- Install prereqs via cpm
- Report possible uncommitted changes back to PR

Author: zakame

.github/workflows/generate-dockerfiles-patches.yml

@@ -3,32 +3,84 @@ name: Generate Dockerfiles/patches
 on:
   push:
     branches:
-      - '**'
+      - master
     tags-ignore:
       - '*'
   pull_request:
+    paths:
+      - cpanfile
+      - config.yml
+      - generate.pl
+      - .github/workflows/generate-dockerfiles-patches.yml
 
 jobs:
   generate:
     runs-on: ubuntu-latest
+    container: perl:devel
+    permissions:
+      contents: read
+      pull-requests: write
+
     steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+
       - name: Set up git user name and email
         run: |
           git config --global user.email "test@github-actions"
           git config --global user.name "GitHub Actions"
-      - uses: actions/checkout@master
-      - name: Install system perl and cpanm
-        run: |
-          sudo apt-get install --no-install-recommends -y perl cpanminus
+
       - name: Install dependencies
         run: |
-          cpanm --quiet --installdeps --notest -L local .
+          cpm install -g
+
       - name: Generate Dockerfiles/patches
+        id: generate
+        shell: bash -euo pipefail -x {0}
         run: |
-          perl -Ilocal/lib/perl5 ./generate.pl
-      - name: Show diffstat (if any)
-        run: |
-          git --no-pager diff --stat HEAD
-      - name: Show diffstat (if any)
+          git config --global --add safe.directory $PWD
+          export DOCKER_PERL_DOWNLOADS_DIR=/tmp/docker-perl-downloads
+          perl ./generate.pl
+          /usr/bin/git --no-pager diff --stat > diffstat.txt
+          if [[ -s diffstat.txt ]]; then
+            echo has_extra_diffs=1 >> $GITHUB_OUTPUT
+          fi
+
+      - name: Setup NodeJS in Perl container (for comment to PR)
+        if: github.event_name == 'pull_request' && steps.generate.outputs.has_extra_diffs
         run: |
-          git --no-pager diff --stat HEAD
+          if ! command -v node; then
+            curl -sL https://deb.nodesource.com/setup_lts.x -o nodesource_setup.sh
+            bash nodesource_setup.sh
+            apt-get install -y --no-install-recommends nodejs
+            npm install -g yarn
+            rm -fr /var/lib/apt/lists/* /var/lib/apt/cache/* nodesource_setup.sh
+          fi
+
+      - name: Comment diffstat of generated changes to PR (if any)
+        if: github.event_name == 'pull_request' && steps.generate.outputs.has_extra_diffs
+        uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
+        with:
+          script: |
+            const fs = require('node:fs')
+            let out = fs.readFileSync('diffstat.txt', 'utf8').trim()
+
+            if (out && context.actor !== 'nektos/act') {
+              const output = `
+              #### :warning: Additional changes generated (missing in commit), see diffstat:
+              <details><summary>Show Output</summary>
+
+              \`\`\`diff
+              ${ out }
+              \`\`\`
+              </details>`
+
+              github.rest.issues.createComment({
+                issue_number: context.issue.number,
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                body: output
+              })
+            } else {
+              console.log(out)
+            }
+