ci: Import run-eslint script from gnome-shell

Since we dropped the legacy configuration, we run eslint directly
instead of via a script. However gnome-shell's variant of the script
also has special treatment of merge requests to only consider errors
in changed lines.

While we strive for zero errors, new errors can appear when we update
eslint or change the configuration. Not blocking merge requests due
to unrelated eslint errors is a good thing, run eslint through a
modified version of the gnome-shell script.

https://gitlab.gnome.org/GNOME/gnome-shell-extensions/merge_requests/90

.gitlab-ci.yml

@@ -3,9 +3,6 @@ stages:
  - source_check
  - build
 
-variables:
- LINT_LOG: "eslint-report.txt"
-
 .only_default: &only_default
     only:
         - branches
@@ -24,11 +21,11 @@ eslint:
   image: registry.gitlab.gnome.org/gnome/gnome-shell/extension-ci:v1
   stage: source_check
   script:
-    - eslint -o $LINT_LOG --no-color || { cat $LINT_LOG; false; }
+    - ./.gitlab-ci/run-eslint.sh
   <<: *only_default
   artifacts:
     paths:
-      - ${LINT_LOG}
+      - reports
     when: on_failure
 
 build-shell-extensions:

.gitlab-ci/run-eslint.sh

@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+
+OUTPUT_REGULAR=reports/lint-report.txt
+OUTPUT_MR=reports/lint-mr-report.txt
+
+SRCDIR=extensions
+
+LINE_CHANGES=changed-lines.txt
+
+is_empty() {
+  (! grep -q . $1)
+}
+
+run_eslint() {
+  # ensure output exists even if eslint doesn't report any errors
+  mkdir -p $(dirname $OUTPUT_REGULAR)
+  touch $OUTPUT_REGULAR
+
+  eslint -f unix -o $OUTPUT_REGULAR $SRCDIR
+}
+
+list_commit_range_additions() {
+  # Turn raw context-less git-diff into a list of
+  # filename:lineno pairs of new (+) lines
+  git diff -U0 "$@" -- 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
+}
+
+# Clean up old files from previous runs
+rm -f $OUTPUT_REGULAR $OUTPUT_MR $LINE_CHANGES
+
+if [ "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+  git fetch $CI_MERGE_REQUEST_PROJECT_URL.git $CI_MERGE_REQUEST_TARGET_BRANCH_NAME
+  branch_point=$(git merge-base HEAD FETCH_HEAD)
+  commit_range=$branch_point...$CI_COMMIT_SHA
+
+  list_commit_range_additions $commit_range > $LINE_CHANGES
+
+  # Don't bother with running lint when no JS changed
+  if is_empty $LINE_CHANGES; then
+    exit 0
+  fi
+fi
+
+echo Generating lint report
+run_eslint
+echo Done.
+
+# Just show the report and succeed when not testing a MR
+if [ -z "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+  cat $OUTPUT_REGULAR
+  exit 0
+fi
+
+copy_matched_lines $OUTPUT_REGULAR $LINE_CHANGES $OUTPUT_MR
+cat $OUTPUT_MR
+is_empty $OUTPUT_MR