ci: Check that documentation is updated as required

.gitlab-ci.yml

@@ -177,10 +177,19 @@ test nightly:
 
 meson shared:
   extends: .meson
+  variables:
+    CI_ARTIFACTS_URL: "${CI_PROJECT_URL}/-/jobs/${CI_JOB_ID}/artifacts/raw/"
   script:
     - meson build --default-library=shared --prefix=$(pwd)/install
     - ninja -C build install
     - ./ci/check-plugins-installed.py install
+    - ninja -C build docs/gst_plugins_cache.json
+    - ci/check-documentation-diff.py
+  artifacts:
+    when: always
+    expire_in: "7 days"
+    paths:
+    - plugins-cache-diffs/
 
 meson static:
   extends: .meson

ci/check-documentation-diff.py

@@ -0,0 +1,20 @@
+#!/usr/bin/python3
+import os, subprocess, sys
+
+if __name__ == "__main__":
+    diffsdir = 'plugins-cache-diffs'
+    os.makedirs(diffsdir, exist_ok=True)
+    res = 0
+    try:
+        subprocess.check_call(['git', 'diff', '--quiet'] )
+    except subprocess.CalledProcessError:
+        diffname = os.path.join(diffsdir, 'plugins_cache.diff')
+        res += 1
+        with open(diffname, 'w') as diff:
+            subprocess.check_call(['git', 'diff'], stdout=diff)
+            print('\033[91mYou have a diff in the documentation cache. Please update with:\033[0m')
+            print('     $ curl %s/%s | git apply -' % (os.environ['CI_ARTIFACTS_URL'], diffname.replace('../', '')))
+
+    if res != 0:
+        print('(note that it might take a few minutes for artefacts to be available on the server)\n')
+        sys.exit(res)