Fixes IDE button on merge requests not working with relative URL config

Closes #46438

app/assets/javascripts/lib/utils/url_utility.js

@@ -87,7 +87,7 @@ export function redirectTo(url) {
 export function webIDEUrl(route = undefined) {
   let returnUrl = `${gon.relative_url_root}/-/ide/`;
   if (route) {
-    returnUrl += `project${route}`;
+    returnUrl += `project${route.replace(new RegExp(`^${gon.relative_url_root}`), '')}`;
   }
   return returnUrl;
 }

changelogs/unreleased/ide-url-util-relative-url-fix.yml

+---
+title: Fixes Web IDE button on merge requests when GitLab is installed with relative
+  URL
+merge_request:
+author:
+type: fixed

spec/javascripts/lib/utils/url_utility_spec.js

+import { webIDEUrl } from '~/lib/utils/url_utility';
+
+describe('URL utility', () => {
+  describe('webIDEUrl', () => {
+    describe('without relative_url_root', () => {
+      it('returns IDE path with route', () => {
+        expect(webIDEUrl('/gitlab-org/gitlab-ce/merge_requests/1')).toBe(
+          '/-/ide/project/gitlab-org/gitlab-ce/merge_requests/1',
+        );
+      });
+    });
+
+    describe('with relative_url_root', () => {
+      beforeEach(() => {
+        gon.relative_url_root = '/gitlab';
+      });
+
+      it('returns IDE path with route', () => {
+        expect(webIDEUrl('/gitlab/gitlab-org/gitlab-ce/merge_requests/1')).toBe(
+          '/gitlab/-/ide/project/gitlab-org/gitlab-ce/merge_requests/1',
+        );
+      });
+    });
+  });
+});