Make default target repo same as source repo

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/327291

Before, the default target repo was set to be the
first item of the project list.
In this MR, we change it where default target repo
is the same as the source project.

app/assets/javascripts/projects/compare/components/repo_dropdown.vue

@@ -46,14 +46,7 @@ export default {
       this.emitTargetProject(repo.name);
     },
     setDefaultRepo() {
-      if (this.isSourceRevision) {
-        this.selectedRepo = this.projectTo;
-        return;
-      }
-
-      const [defaultTargetProject] = this.projectsFrom;
-      this.emitTargetProject(defaultTargetProject.name);
-      this.selectedRepo = defaultTargetProject;
+      this.selectedRepo = this.projectTo;
     },
     emitTargetProject(name) {
       if (!this.isSourceRevision) {

spec/frontend/projects/compare/components/repo_dropdown_spec.js

-import { GlDropdown } from '@gitlab/ui';
+import { GlDropdown, GlDropdownItem } from '@gitlab/ui';
 import { shallowMount } from '@vue/test-utils';
 import RepoDropdown from '~/projects/compare/components/repo_dropdown.vue';
 
@@ -69,12 +69,12 @@ describe('RepoDropdown component', () => {
       createComponent({ paramsName: 'from' });
     });
 
-    it('set hidden input of the first project', () => {
-      expect(findHiddenInput().attributes('value')).toBe(projectFromId);
+    it('set hidden input of the selected project', () => {
+      expect(findHiddenInput().attributes('value')).toBe(projectToId);
     });
 
-    it('displays the first project name initially in the dropdown', () => {
-      expect(findGlDropdown().props('text')).toBe(projectFromName);
+    it('displays matching project name of the source revision initially in the dropdown', () => {
+      expect(findGlDropdown().props('text')).toBe(projectToName);
     });
 
     it('updates the hiddin input value when onClick method is triggered', async () => {
@@ -84,15 +84,13 @@ describe('RepoDropdown component', () => {
       expect(findHiddenInput().attributes('value')).toBe(repoId);
     });
 
-    it('emits initial `changeTargetProject` event with target project', () => {
-      expect(wrapper.emitted('changeTargetProject')).toEqual([[projectFromName]]);
-    });
-
     it('emits `changeTargetProject` event when another target project is selected', async () => {
-      const newTargetProject = 'new-from-name';
-      wrapper.vm.$emit('changeTargetProject', newTargetProject);
+      const index = 1;
+      const { projectsFrom } = defaultProvide;
+      findGlDropdown().findAll(GlDropdownItem).at(index).vm.$emit('click');
       await wrapper.vm.$nextTick();
-      expect(wrapper.emitted('changeTargetProject')[1]).toEqual([newTargetProject]);
+
+      expect(wrapper.emitted('changeTargetProject')[0][0]).toEqual(projectsFrom[index].name);
     });
   });
 });