Separate workflow for autoconf temporary

Author: corona10

.github/workflows/build.yml

@@ -40,15 +40,43 @@ jobs:
     if: fromJSON(needs.check_source.outputs.run-docs)
     uses: ./.github/workflows/reusable-docs.yml
 
-  check_generated_files:
+  check_autoconf_regen:
     name: 'Check if generated files are up to date'
     # Don't use ubuntu-latest but a specific version to make the job
     # reproducible: to get the same tools versions (autoconf, aclocal, ...)
     runs-on: ubuntu-24.04
     container:
       image: ghcr.io/python/autoconf:2024.10.11.11293396815
-      env:
-        DEBIAN_FRONTEND: noninteractive
+        timeout-minutes: 60
+    needs: check_source
+    if: needs.check_source.outputs.run_tests == 'true'
+    steps:
+      - uses: actions/checkout@v4
+      - name: Runner image version
+        run: echo "IMAGE_VERSION=${ImageVersion}" >> $GITHUB_ENV
+      - name: Regenerate autoconf files
+        # Same command used by Tools/build/regen-configure.sh ($AUTORECONF)
+        run: autoreconf -ivf -Werror
+      - name: Check for changes
+        run: |
+          git add -u
+          changes=$(git status --porcelain)
+          # Check for changes in regenerated files
+          if test -n "$changes"; then
+            echo "Generated files not up to date."
+            echo "Perhaps you forgot to run make regen-all or build.bat --regen. ;)"
+            echo "configure files must be regenerated with a specific version of autoconf."
+            echo "$changes"
+            echo ""
+            git diff --staged || true
+            exit 1
+          fi
+
+  check_generated_files:
+    name: 'Check if generated files are up to date'
+    # Don't use ubuntu-latest but a specific version to make the job
+    # reproducible: to get the same tools versions (autoconf, aclocal, ...)
+    runs-on: ubuntu-24.04
     timeout-minutes: 60
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
@@ -83,9 +111,6 @@ jobs:
         run: |
           # Build Python with the libpython dynamic library
           ./configure --config-cache --with-pydebug --enable-shared
-      - name: Regenerate autoconf files
-        # Same command used by Tools/build/regen-configure.sh ($AUTORECONF)
-        run: autoreconf -ivf -Werror
       - name: Build CPython
         run: |
           make -j4 regen-all