ci: Use wrapper to run eslint

The eslint job report its results as artifacts in junit format,
so that gitlab can present them in its UI.

However many psople miss that, and unsuccessfully check the logs
instead.

Address this by using a simplified version of gnome-shell's eslint
wrapper, so we can report results both on stdout and in a file
without re-running the linter.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/262>

.gitlab-ci.yml

@@ -107,7 +107,8 @@ eslint:
   stage: review
   <<: *prereview_req
   script:
-    - eslint -o $LINT_LOG -f junit --resolve-plugins-relative-to $(npm root -g) extensions
+    - export NODE_PATH=$(npm root -g)
+    - ./.gitlab-ci/run-eslint --output-file ${LINT_LOG} --format junit --stdout
   artifacts:
     paths:
       - ${LINT_LOG}

.gitlab-ci/run-eslint

@@ -0,0 +1,54 @@
+#!/usr/bin/env node
+
+const {ESLint} = require('eslint');
+
+console.log(`Running ESLint version ${ESLint.version}...`);
+
+const fs = require('fs');
+const path = require('path');
+
+function hasOption(...names) {
+    return process.argv.some(arg => names.includes(arg));
+}
+
+function getOption(...names) {
+    const optIndex =
+        process.argv.findIndex(arg => names.includes(arg)) + 1;
+
+    if (optIndex === 0)
+        return undefined;
+
+    return process.argv[optIndex];
+}
+
+(async function main() {
+    const outputOption = getOption('--output-file', '-o');
+    const outputPath = outputOption ? path.resolve(outputOption) : null;
+
+    const sourceDir = path.dirname(process.argv[1]);
+    process.chdir(path.resolve(sourceDir, '..'));
+
+    const sources = ['extensions'];
+    const eslint = new ESLint();
+
+    const results = await eslint.lintFiles(sources);
+    const formatter = await eslint.loadFormatter(getOption('--format', '-f'));
+    const resultText = formatter.format(results);
+
+    if (outputPath) {
+        fs.mkdirSync(path.dirname(outputPath), {recursive: true});
+        fs.writeFileSync(outputPath, resultText);
+
+        if (hasOption('--stdout')) {
+            const consoleFormatter = await eslint.loadFormatter();
+            console.log(consoleFormatter.format(results));
+        }
+    } else {
+        console.log(resultText);
+    }
+
+    process.exitCode = results.some(r => r.errorCount > 0) ? 1 : 0;
+})().catch((error) => {
+    process.exitCode = 1;
+    console.error(error);
+});