ci: Add eslint job to review stage

We have now reduced the number of eslint errors enough to add it to
the CI pipeline. There are still plenty of errors left though, so we
cannot simply run eslint and fail on any errors. So instead, run it
through a fancy script that:

 - generates an eslint report using the "regular" configuration
 - generates an eslint report using the "legacy" configuration
 - creates a combined report with errors common to both configurations

When the pipeline is running for a branch or tag, the final report is
printed out and the job succeeds (we know there are errors left);
when the pipelne is running for a merge request, we fail if any errors
are reported for the lines modified/added by the MR.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/627

.gitlab-ci.yml

@@ -38,6 +38,17 @@ js_check:
             - ${JS_LOG}
         when: on_failure
 
+eslint:
+    image: registry.gitlab.gnome.org/gnome/gnome-shell/extension-ci:v1
+    stage: review
+    script:
+        - ./.gitlab-ci/run-eslint.sh
+    <<: *only_default
+    artifacts:
+        paths:
+            - reports
+        when: always
+
 build:
     image: registry.gitlab.gnome.org/gnome/mutter/master:v2
     stage: build

.gitlab-ci/run-eslint.sh

@@ -0,0 +1,94 @@
+#!/usr/bin/bash
+
+OUTPUT_REGULAR=reports/lint-regular-report.txt
+OUTPUT_LEGACY=reports/lint-legacy-report.txt
+OUTPUT_FINAL=reports/lint-common-report.txt
+
+OUTPUT_MR=reports/lint-mr-report.txt
+
+LINE_CHANGES=changed-lines.txt
+
+is_empty() {
+  (! grep -q . $1)
+}
+
+run_eslint() {
+  ARGS_LEGACY='--config lint/eslintrc-legacy.json'
+
+  local extra_args=ARGS_$1
+  local output=OUTPUT_$1
+  eslint -f unix ${!extra_args} -o ${!output} js
+}
+
+list_commit_range_additions() {
+  # Turn raw context-less git-diff into a list of
+  # filename:lineno pairs of new (+) lines
+  git diff -U0 "$@" -- js |
+  awk '
+    BEGIN { file=""; }
+    /^+++ b/ { file=substr($0,7); }
+    /^@@ / {
+        len = split($3,a,",")
+        start=a[1]
+        count=(len > 1) ? a[2] : 1
+
+        for (line=start; line<start+count; line++)
+            printf "%s/%s:%d:\n",ENVIRON["PWD"],file,line;
+    }'
+}
+
+copy_matched_lines() {
+  local source=$1
+  local matches=$2
+  local target=$3
+
+  echo -n > $target
+  for l in $(<$matches); do
+    grep $l $source >> $target
+  done
+}
+
+create_common() {
+  # comm requires sorted input;
+  # we also strip the error message to make the following a "common" error:
+  # regular:
+  #  file.js:42:23 Indentation of 55, expected 42
+  # legacy:
+  #  file.js:42:23 Indentation of 55, extected 24
+  prepare() {
+    sed 's: .*::' $1 | sort
+  }
+
+  comm -12 <(prepare $OUTPUT_REGULAR) <(prepare $OUTPUT_LEGACY) >$OUTPUT_FINAL.tmp
+
+  # Now add back the stripped error messages
+  copy_matched_lines $OUTPUT_REGULAR $OUTPUT_FINAL.tmp $OUTPUT_FINAL
+  rm $OUTPUT_FINAL.tmp
+}
+
+if [ "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+  commit_range=origin/$CI_MERGE_REQUEST_TARGET_BRANCH_NAME...$CI_COMMIT_SHA
+  list_commit_range_additions $commit_range > $LINE_CHANGES
+
+  # Don't bother with running lint when no JS changed
+  if is_empty $LINE_CHANGES; then
+    exit 0
+  fi
+fi
+
+echo Generating lint report using regular configuration
+run_eslint REGULAR
+echo Generating lint report using legacy configuration
+run_eslint LEGACY
+echo Done.
+create_common
+
+# Just show the report and succeed when not testing a MR
+if [ -z "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+  cat $OUTPUT_FINAL
+  exit 0
+fi
+
+copy_matched_lines $OUTPUT_FINAL $LINE_CHANGES $OUTPUT_MR
+cat $OUTPUT_MR
+is_empty $OUTPUT_MR