Check meson.build formatting in CI

Add a new CI job that checks whether all meson.build files in the
repository are formatted in the exact same way as "muon fmt" would
format them.  This enforces formatting consistency across all
meson.build files in the repository and enables updating their contents
using dedicated tools, e.g. "meson rewrite".

.gitlab-ci.yml

@@ -615,6 +615,29 @@ coccinelle:
     - util/check-cocci
     - if test "$(git status --porcelain | grep -Ev '\?\?' | wc -l)" -gt "0"; then git status --short; exit 1; fi
 
+meson-format:
+  ######################################################################
+  # Revert to using the "precheck_job" anchor after the "base" image is
+  # upgraded to Debian trixie, which has muon 0.4.0.
+  <<: *default_triggering_rules
+  <<: *debian_sid_amd64_image
+  stage: precheck
+  ######################################################################
+  needs: []
+  script:
+    - git ls-files "*meson.build" | xargs muon-meson fmt -i
+    - git diff > meson-format.patch
+    - if test "$(git status --porcelain | grep -Ev '\?\?' | wc -l)" -gt "0"; then git status --short; exit 1; fi
+  artifacts:
+    paths:
+      - meson-format.patch
+    expire_in: "1 week"
+    when: on_failure
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+      changes:
+        - "**/meson.build"
+
 doctest:
   <<: *precheck_job
   needs: []

meson.build

@@ -1650,7 +1650,7 @@ print(release_date, end="")
 if doc_opt.allowed()
     release_date = ''
     if python.found()
-      release_date = run_command(python, ['-c', get_release_date], check: true).stdout()
+        release_date = run_command(python, ['-c', get_release_date], check: true).stdout()
     endif
 
     man_srcconf = man_srcset.apply(config, strict: false)