bpo-44035: Check autoconf files thoroughly (GH-29935)

Check that users don't push changes with outdated or patched autoconf.
The presence of runstatedir option and aclocal 1.16.3 are good markers.

Use my container image to regenerate autoconf files. "Check for changes"
will fail later when any file is regenerated.

Use ccache in check_generated_files to speed up testing.

.github/workflows/build.yml

@@ -64,6 +64,18 @@ jobs:
       - uses: actions/setup-python@v2
       - name: Install Dependencies
         run: sudo ./.github/workflows/posix-deps-apt.sh
+      - name: Add ccache to PATH
+        run: echo "PATH=/usr/lib/ccache:$PATH" >> $GITHUB_ENV
+      - name: Configure ccache action
+        uses: hendrikmuhs/ccache-action@v1
+      - name: Check Autoconf version 2.69 and aclocal 1.16.3
+        run: |
+          grep "Generated by GNU Autoconf 2.69" configure
+          grep "aclocal 1.16.3" aclocal.m4
+          grep -q "runstatedir" configure
+          grep -q "PKG_PROG_PKG_CONFIG" aclocal.m4
+      - name: Regenerate autoconf files
+        run: docker run --rm -v $(pwd):/src quay.io/tiran/cpython_autoconf:269
       - name: Build CPython
         run: |
           # Build Python with the libpython dynamic library
@@ -75,9 +87,10 @@ jobs:
           git add -u
           changes=$(git status --porcelain)
           # Check for changes in regenerated files
-          if ! test -z "$changes"
-          then
-            echo "Generated files not up to date. Perhaps you forgot to run make regen-all or build.bat --regen ;)"
+          if test -n "$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, unpatched version of autoconf."
             echo "$changes"
             exit 1
           fi
@@ -85,10 +98,6 @@ jobs:
         run: make smelly
       - name: Check limited ABI symbols
         run: make check-limited-abi
-      - name: Check Autoconf version 2.69
-        run: |
-          grep "Generated by GNU Autoconf 2.69" configure
-          grep "PKG_PROG_PKG_CONFIG" aclocal.m4
 
   build_win32:
     name: 'Windows (x86)'

.gitignore

@@ -115,6 +115,8 @@ Tools/unicode/data/
 /config.log
 /config.status
 /config.status.lineno
+# hendrikmuhs/ccache-action@v1
+/.ccache
 /platform
 /profile-clean-stamp
 /profile-run-stamp

Misc/NEWS.d/next/Build/2021-12-06-09-31-27.bpo-44035.BiO4XC.rst

@@ -0,0 +1,2 @@
+CI now verifies that autoconf files have been regenerated with a current and
+unpatched autoconf package.