ci: Check snippets in coding style

To avoid having the coding style get out of sync with the actual
coding style in the future, run eslint on the individual snippets
when either the guide or the linter config change.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3146>

.gitlab-ci.yml

@@ -149,6 +149,21 @@ eslint:
       junit: ${LINT_LOG}
     when: always
 
+eslint-doc:
+  extends:
+    - .fdo.distribution-image@fedora
+    - .gnome-shell.fedora
+  stage: review
+  script:
+    - export NODE_PATH=$(npm root -g)
+    - ./.gitlab-ci/eslint-coding-style.sh
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+      changes:
+        - HACKING.md
+        - .eslintrc.yml
+        - lint/*
+
 potfile_c_check:
   extends:
     - .fdo.distribution-image@fedora

.gitlab-ci/eslint-coding-style.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+
+SRCDIR=$(realpath $(dirname $0)/..)
+OUTDIR=$(mktemp --directory --tmpdir=$SRCDIR)
+trap "rm -rf $OUTDIR" EXIT
+
+# Turn ```javascript``` code snippets in the
+# style guide into .js files in $OUTDIR
+awk --assign dir=$OUTDIR -- '
+  BEGIN {
+    do_print = 0;
+    cur = 0;
+  }
+
+  # end of code snippet
+  /```$/ {
+    do_print = 0;
+    cur++;
+  }
+
+  do_print {
+    # remove one level of indent
+    sub("    ","")
+
+    # the following are class snippets, turn them
+    # into functions to not confuse eslint
+    sub("moveActor","function moveActor")
+    sub("desaturateActor","function desaturateActor")
+
+    # finally, append to the currently generated .js file
+    print >> dir "/" cur ".js";
+  }
+
+  # start of code snippet
+  /```javascript$/ {
+    do_print = 1;
+  }
+' HACKING.md
+
+eslint \
+  --rule 'no-undef: off' \
+  --rule 'no-unused-vars: off' \
+  --rule 'no-invalid-this: off' $OUTDIR/*.js