ci: Check that files with translatable strings are listed in POTFILES

Also known as "Piotr Drąg Bot".

We will soon make sure that files processed by xgettext don't use template
strings. To make that check as adequate as possible, ensure that no source
code files are missing from POTFILES.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/1016

.gitlab-ci.yml

@@ -46,6 +46,13 @@ eslint:
             - reports
         when: always
 
+potfile_check:
+    image: registry.gitlab.gnome.org/gnome/gnome-shell/extension-ci:v1
+    stage: review
+    script:
+        - ./.gitlab-ci/check-potfiles.sh
+    <<: *only_default
+
 build:
     image: registry.gitlab.gnome.org/gnome/mutter/master:v3
     stage: build

.gitlab-ci/check-potfiles.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+srcdirs="js src subprojects/extensions-tool"
+globs=('*.js' '*.c')
+
+# find source files that contain gettext keywords
+files=$(grep -lR ${globs[@]/#/--include=} '\(gettext\|[^I_)]_\)(' $srcdirs)
+
+# find those that aren't listed in POTFILES.in
+missing=$(for f in $files; do ! grep -q ^$f po/POTFILES.in && echo $f; done)
+
+if [ ${#missing} -eq 0 ]; then
+  exit 0
+fi
+
+cat >&2 <<EOT
+
+The following files are missing from po/POTFILES.po:
+
+EOT
+for f in $missing; do
+  echo "  $f" >&2
+done
+echo >&2
+
+exit 1