Merge branch '14615-add-compare-repo-dropdown' into 'master'

Restyle compare revision and add repo dropdown [RUN ALL RSPEC] [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!52967

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

 <script>
 import { GlButton } from '@gitlab/ui';
 import csrf from '~/lib/utils/csrf';
-import RevisionDropdown from './revision_dropdown.vue';
+import RevisionCard from './revision_card.vue';
 
 export default {
   csrf,
   components: {
-    RevisionDropdown,
+    RevisionCard,
     GlButton,
   },
   props: {
@@ -48,32 +48,42 @@ export default {
 <template>
   <form
     ref="form"
-    class="form-inline js-requires-input js-signature-container"
+    class="js-requires-input js-signature-container"
     method="POST"
     :action="projectCompareIndexPath"
   >
     <input :value="$options.csrf.token" type="hidden" name="authenticity_token" />
-    <revision-dropdown
+    <div
+      class="gl-lg-flex-direction-row gl-lg-display-flex gl-align-items-center compare-revision-cards"
+    >
+      <revision-card
         :refs-project-path="refsProjectPath"
         revision-text="Source"
         params-name="to"
         :params-branch="paramsTo"
       />
-    <div class="compare-ellipsis gl-display-inline" data-testid="ellipsis">...</div>
-    <revision-dropdown
+      <div
+        class="compare-ellipsis gl-display-flex gl-justify-content-center gl-align-items-center gl-my-4 gl-md-my-0"
+        data-testid="ellipsis"
+      >
+        ...
+      </div>
+      <revision-card
         :refs-project-path="refsProjectPath"
         revision-text="Target"
         params-name="from"
         :params-branch="paramsFrom"
       />
-    <gl-button category="primary" variant="success" class="gl-ml-3" @click="onSubmit">
+    </div>
+    <div class="gl-mt-4">
+      <gl-button category="primary" variant="success" @click="onSubmit">
         {{ s__('CompareRevisions|Compare') }}
       </gl-button>
       <gl-button
         v-if="projectMergeRequestPath"
         :href="projectMergeRequestPath"
         data-testid="projectMrButton"
-      class="btn btn-default gl-button gl-ml-3"
+        class="btn btn-default gl-button"
       >
         {{ s__('CompareRevisions|View open merge request') }}
       </gl-button>
@@ -81,9 +91,10 @@ export default {
         v-else-if="createMrPath"
         :href="createMrPath"
         data-testid="createMrButton"
-      class="btn btn-default gl-button gl-ml-3"
+        class="btn btn-default gl-button"
       >
         {{ s__('CompareRevisions|Create merge request') }}
       </gl-button>
+    </div>
   </form>
 </template>

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

+<script>
+import { GlButton } from '@gitlab/ui';
+import csrf from '~/lib/utils/csrf';
+import RevisionDropdown from './revision_dropdown_legacy.vue';
+
+export default {
+  csrf,
+  components: {
+    RevisionDropdown,
+    GlButton,
+  },
+  props: {
+    projectCompareIndexPath: {
+      type: String,
+      required: true,
+    },
+    refsProjectPath: {
+      type: String,
+      required: true,
+    },
+    paramsFrom: {
+      type: String,
+      required: false,
+      default: null,
+    },
+    paramsTo: {
+      type: String,
+      required: false,
+      default: null,
+    },
+    projectMergeRequestPath: {
+      type: String,
+      required: true,
+    },
+    createMrPath: {
+      type: String,
+      required: true,
+    },
+  },
+  methods: {
+    onSubmit() {
+      this.$refs.form.submit();
+    },
+  },
+};
+</script>
+
+<template>
+  <form
+    ref="form"
+    class="form-inline js-requires-input js-signature-container"
+    method="POST"
+    :action="projectCompareIndexPath"
+  >
+    <input :value="$options.csrf.token" type="hidden" name="authenticity_token" />
+    <revision-dropdown
+      :refs-project-path="refsProjectPath"
+      revision-text="Source"
+      params-name="to"
+      :params-branch="paramsTo"
+    />
+    <div class="compare-ellipsis gl-display-inline" data-testid="ellipsis">...</div>
+    <revision-dropdown
+      :refs-project-path="refsProjectPath"
+      revision-text="Target"
+      params-name="from"
+      :params-branch="paramsFrom"
+    />
+    <gl-button category="primary" variant="success" class="gl-ml-3" @click="onSubmit">
+      {{ s__('CompareRevisions|Compare') }}
+    </gl-button>
+    <gl-button
+      v-if="projectMergeRequestPath"
+      :href="projectMergeRequestPath"
+      data-testid="projectMrButton"
+      class="btn btn-default gl-button gl-ml-3"
+    >
+      {{ s__('CompareRevisions|View open merge request') }}
+    </gl-button>
+    <gl-button
+      v-else-if="createMrPath"
+      :href="createMrPath"
+      data-testid="createMrButton"
+      class="btn btn-default gl-button gl-ml-3"
+    >
+      {{ s__('CompareRevisions|Create merge request') }}
+    </gl-button>
+  </form>
+</template>

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

+<script>
+import { GlDropdown, GlDropdownItem, GlSearchBoxByType } from '@gitlab/ui';
+
+const SOURCE_PARAM_NAME = 'to';
+
+export default {
+  components: {
+    GlDropdown,
+    GlDropdownItem,
+    GlSearchBoxByType,
+  },
+  inject: ['projectTo', 'projectsFrom'],
+  props: {
+    paramsName: {
+      type: String,
+      required: true,
+    },
+  },
+  data() {
+    return {
+      searchTerm: '',
+      selectedRepo: {},
+    };
+  },
+  computed: {
+    filteredRepos() {
+      const lowerCaseSearchTerm = this.searchTerm.toLowerCase();
+
+      return this?.projectsFrom.filter(({ name }) =>
+        name.toLowerCase().includes(lowerCaseSearchTerm),
+      );
+    },
+    isSourceRevision() {
+      return this.paramsName === SOURCE_PARAM_NAME;
+    },
+    inputName() {
+      return `${this.paramsName}_project_id`;
+    },
+  },
+  mounted() {
+    this.setDefaultRepo();
+  },
+  methods: {
+    onClick(repo) {
+      this.selectedRepo = repo;
+      this.emitTargetProject(repo.name);
+    },
+    setDefaultRepo() {
+      if (this.isSourceRevision) {
+        this.selectedRepo = this.projectTo;
+        return;
+      }
+
+      const [defaultTargetProject] = this.projectsFrom;
+      this.emitTargetProject(defaultTargetProject.name);
+      this.selectedRepo = defaultTargetProject;
+    },
+    emitTargetProject(name) {
+      if (!this.isSourceRevision) {
+        this.$emit('changeTargetProject', name);
+      }
+    },
+  },
+};
+</script>
+
+<template>
+  <div>
+    <input type="hidden" :name="inputName" :value="selectedRepo.id" />
+    <gl-dropdown
+      :text="selectedRepo.name"
+      :header-text="s__(`CompareRevisions|Select target project`)"
+      class="gl-w-full gl-font-monospace gl-sm-pr-3"
+      toggle-class="gl-min-w-0"
+      :disabled="isSourceRevision"
+    >
+      <template #header>
+        <gl-search-box-by-type v-if="!isSourceRevision" v-model.trim="searchTerm" />
+      </template>
+      <template v-if="!isSourceRevision">
+        <gl-dropdown-item
+          v-for="repo in filteredRepos"
+          :key="repo.id"
+          is-check-item
+          :is-checked="selectedRepo.id === repo.id"
+          @click="onClick(repo)"
+        >
+          {{ repo.name }}
+        </gl-dropdown-item>
+      </template>
+    </gl-dropdown>
+  </div>
+</template>

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

+<script>
+import { GlCard } from '@gitlab/ui';
+import RepoDropdown from './repo_dropdown.vue';
+import RevisionDropdown from './revision_dropdown.vue';
+
+export default {
+  components: {
+    RepoDropdown,
+    RevisionDropdown,
+    GlCard,
+  },
+  props: {
+    refsProjectPath: {
+      type: String,
+      required: true,
+    },
+    revisionText: {
+      type: String,
+      required: true,
+    },
+    paramsName: {
+      type: String,
+      required: true,
+    },
+    paramsBranch: {
+      type: String,
+      required: false,
+      default: null,
+    },
+  },
+  data() {
+    return {
+      selectedRefsProjectPath: this.refsProjectPath,
+    };
+  },
+  methods: {
+    onChangeTargetProject(targetProjectName) {
+      if (this.paramsName === 'from') {
+        this.selectedRefsProjectPath = `/${targetProjectName}/refs`;
+      }
+    },
+  },
+};
+</script>
+
+<template>
+  <gl-card header-class="gl-py-2 gl-px-3 gl-font-weight-bold" body-class="gl-px-3">
+    <template #header>
+      {{ s__(`CompareRevisions|${revisionText}`) }}
+    </template>
+    <div class="gl-sm-display-flex gl-align-items-center">
+      <repo-dropdown
+        class="gl-sm-w-half"
+        :params-name="paramsName"
+        @changeTargetProject="onChangeTargetProject"
+      />
+      <revision-dropdown
+        class="gl-sm-w-half gl-mt-3 gl-sm-mt-0"
+        :refs-project-path="selectedRefsProjectPath"
+        :params-name="paramsName"
+        :params-branch="paramsBranch"
+      />
+    </div>
+  </gl-card>
+</template>

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

@@ -4,6 +4,8 @@ import createFlash from '~/flash';
 import axios from '~/lib/utils/axios_utils';
 import { s__ } from '~/locale';
 
+const emptyDropdownText = s__('CompareRevisions|Select branch/tag');
+
 export default {
   components: {
     GlDropdown,
@@ -16,10 +18,6 @@ export default {
       type: String,
       required: true,
     },
-    revisionText: {
-      type: String,
-      required: true,
-    },
     paramsName: {
       type: String,
       required: true,
@@ -55,12 +53,24 @@ export default {
       return this.filteredTags.length;
     },
   },
+  watch: {
+    refsProjectPath(newRefsProjectPath, oldRefsProjectPath) {
+      if (newRefsProjectPath !== oldRefsProjectPath) {
+        this.fetchBranchesAndTags(true);
+      }
+    },
+  },
   mounted() {
     this.fetchBranchesAndTags();
   },
   methods: {
-    fetchBranchesAndTags() {
+    fetchBranchesAndTags(reset = false) {
       const endpoint = this.refsProjectPath;
+      this.loading = true;
+
+      if (reset) {
+        this.selectedRevision = emptyDropdownText;
+      }
 
       return axios
         .get(endpoint)
@@ -70,9 +80,9 @@ export default {
         })
         .catch(() => {
           createFlash({
-            message: `${s__(
-              'CompareRevisions|There was an error while updating the branch/tag list. Please try again.',
-            )}`,
+            message: s__(
+              'CompareRevisions|There was an error while loading the branch/tag list. Please try again.',
+            ),
           });
         })
         .finally(() => {
@@ -80,7 +90,7 @@ export default {
         });
     },
     getDefaultBranch() {
-      return this.paramsBranch || s__('CompareRevisions|Select branch/tag');
+      return this.paramsBranch || emptyDropdownText;
     },
     onClick(revision) {
       this.selectedRevision = revision;
@@ -93,19 +103,13 @@ export default {
 </script>
 
 <template>
-  <div class="form-group compare-form-group" :class="`js-compare-${paramsName}-dropdown`">
-    <div class="input-group inline-input-group">
-      <span class="input-group-prepend">
-        <div class="input-group-text">
-          {{ revisionText }}
-        </div>
-      </span>
+  <div :class="`js-compare-${paramsName}-dropdown`">
     <input type="hidden" :name="paramsName" :value="selectedRevision" />
     <gl-dropdown
-        class="gl-flex-grow-1 gl-flex-basis-0 gl-min-w-0 gl-font-monospace"
-        toggle-class="form-control compare-dropdown-toggle js-compare-dropdown gl-min-w-0 gl-rounded-top-left-none! gl-rounded-bottom-left-none!"
+      class="gl-w-full gl-font-monospace"
+      toggle-class="form-control compare-dropdown-toggle js-compare-dropdown gl-min-w-0"
       :text="selectedRevision"
-        header-text="Select Git revision"
+      :header-text="s__('CompareRevisions|Select Git revision')"
       :loading="loading"
     >
       <template #header>
@@ -141,5 +145,4 @@ export default {
       </gl-dropdown-item>
     </gl-dropdown>
   </div>
-  </div>
 </template>

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

+<script>
+import { GlDropdown, GlDropdownItem, GlSearchBoxByType, GlDropdownSectionHeader } from '@gitlab/ui';
+import createFlash from '~/flash';
+import axios from '~/lib/utils/axios_utils';
+import { s__ } from '~/locale';
+
+export default {
+  components: {
+    GlDropdown,
+    GlDropdownItem,
+    GlDropdownSectionHeader,
+    GlSearchBoxByType,
+  },
+  props: {
+    refsProjectPath: {
+      type: String,
+      required: true,
+    },
+    revisionText: {
+      type: String,
+      required: true,
+    },
+    paramsName: {
+      type: String,
+      required: true,
+    },
+    paramsBranch: {
+      type: String,
+      required: false,
+      default: null,
+    },
+  },
+  data() {
+    return {
+      branches: [],
+      tags: [],
+      loading: true,
+      searchTerm: '',
+      selectedRevision: this.getDefaultBranch(),
+    };
+  },
+  computed: {
+    filteredBranches() {
+      return this.branches.filter((branch) =>
+        branch.toLowerCase().includes(this.searchTerm.toLowerCase()),
+      );
+    },
+    hasFilteredBranches() {
+      return this.filteredBranches.length;
+    },
+    filteredTags() {
+      return this.tags.filter((tag) => tag.toLowerCase().includes(this.searchTerm.toLowerCase()));
+    },
+    hasFilteredTags() {
+      return this.filteredTags.length;
+    },
+  },
+  mounted() {
+    this.fetchBranchesAndTags();
+  },
+  methods: {
+    fetchBranchesAndTags() {
+      const endpoint = this.refsProjectPath;
+
+      return axios
+        .get(endpoint)
+        .then(({ data }) => {
+          this.branches = data.Branches;
+          this.tags = data.Tags;
+        })
+        .catch(() => {
+          createFlash({
+            message: `${s__(
+              'CompareRevisions|There was an error while updating the branch/tag list. Please try again.',
+            )}`,
+          });
+        })
+        .finally(() => {
+          this.loading = false;
+        });
+    },
+    getDefaultBranch() {
+      return this.paramsBranch || s__('CompareRevisions|Select branch/tag');
+    },
+    onClick(revision) {
+      this.selectedRevision = revision;
+    },
+    onSearchEnter() {
+      this.selectedRevision = this.searchTerm;
+    },
+  },
+};
+</script>
+
+<template>
+  <div class="form-group compare-form-group" :class="`js-compare-${paramsName}-dropdown`">
+    <div class="input-group inline-input-group">
+      <span class="input-group-prepend">
+        <div class="input-group-text">
+          {{ revisionText }}
+        </div>
+      </span>
+      <input type="hidden" :name="paramsName" :value="selectedRevision" />
+      <gl-dropdown
+        class="gl-flex-grow-1 gl-flex-basis-0 gl-min-w-0 gl-font-monospace"
+        toggle-class="form-control compare-dropdown-toggle js-compare-dropdown gl-min-w-0 gl-rounded-top-left-none! gl-rounded-bottom-left-none!"
+        :text="selectedRevision"
+        header-text="Select Git revision"
+        :loading="loading"
+      >
+        <template #header>
+          <gl-search-box-by-type
+            v-model.trim="searchTerm"
+            :placeholder="s__('CompareRevisions|Filter by Git revision')"
+            @keyup.enter="onSearchEnter"
+          />
+        </template>
+        <gl-dropdown-section-header v-if="hasFilteredBranches">
+          {{ s__('CompareRevisions|Branches') }}
+        </gl-dropdown-section-header>
+        <gl-dropdown-item
+          v-for="(branch, index) in filteredBranches"
+          :key="`branch${index}`"
+          is-check-item
+          :is-checked="selectedRevision === branch"
+          @click="onClick(branch)"
+        >
+          {{ branch }}
+        </gl-dropdown-item>
+        <gl-dropdown-section-header v-if="hasFilteredTags">
+          {{ s__('CompareRevisions|Tags') }}
+        </gl-dropdown-section-header>
+        <gl-dropdown-item
+          v-for="(tag, index) in filteredTags"
+          :key="`tag${index}`"
+          is-check-item
+          :is-checked="selectedRevision === tag"
+          @click="onClick(tag)"
+        >
+          {{ tag }}
+        </gl-dropdown-item>
+      </gl-dropdown>
+    </div>
+  </div>
+</template>

app/assets/javascripts/projects/compare/index.js

 import Vue from 'vue';
 import CompareApp from './components/app.vue';
+import CompareAppLegacy from './components/app_legacy.vue';
 
 export default function init() {
   const el = document.getElementById('js-compare-selector');
+
+  if (gon.features?.compareRepoDropdown) {
     const {
       refsProjectPath,
       paramsFrom,
@@ -10,6 +13,8 @@ export default function init() {
       projectCompareIndexPath,
       projectMergeRequestPath,
       createMrPath,
+      projectTo,
+      projectsFrom,
     } = el.dataset;
 
     return new Vue({
@@ -17,6 +22,10 @@ export default function init() {
       components: {
         CompareApp,
       },
+      provide: {
+        projectTo: JSON.parse(projectTo),
+        projectsFrom: JSON.parse(projectsFrom),
+      },
       render(createElement) {
         return createElement(CompareApp, {
           props: {
@@ -30,4 +39,33 @@ export default function init() {
         });
       },
     });
+  }
+
+  const {
+    refsProjectPath,
+    paramsFrom,
+    paramsTo,
+    projectCompareIndexPath,
+    projectMergeRequestPath,
+    createMrPath,
+  } = el.dataset;
+
+  return new Vue({
+    el,
+    components: {
+      CompareAppLegacy,
+    },
+    render(createElement) {
+      return createElement(CompareAppLegacy, {
+        props: {
+          refsProjectPath,
+          paramsFrom,
+          paramsTo,
+          projectCompareIndexPath,
+          projectMergeRequestPath,
+          createMrPath,
+        },
+      });
+    },
+  });
 }

app/assets/stylesheets/pages/projects.scss

@@ -1008,6 +1008,18 @@ pre.light-well {
   }
 }
 
+.compare-revision-cards {
+  @media (min-width: $breakpoint-lg) {
+    .gl-card {
+      width: calc(50% - 15px);
+    }
+
+    .compare-ellipsis {
+      width: 30px;
+    }
+  }
+}
+
 .clearable-input {
   position: relative;
 

app/assets/stylesheets/utilities.scss

@@ -157,3 +157,17 @@
     margin-bottom: $gl-spacing-scale-4 !important;
   }
 }
+
+// Will be moved to @gitlab/ui in https://gitlab.com/gitlab-org/gitlab-ui/-/issues/1168
+.gl-sm-pr-3 {
+  @media (min-width: $breakpoint-sm) {
+    padding-right: $gl-spacing-scale-3;
+  }
+}
+
+// Will be moved to @gitlab/ui in https://gitlab.com/gitlab-org/gitlab-ui/-/issues/1168
+.gl-sm-w-half {
+  @media (min-width: $breakpoint-sm) {
+    width: 50%;
+  }
+}

app/controllers/projects/compare_controller.rb

@@ -20,6 +20,10 @@ class Projects::CompareController < Projects::ApplicationController
   # Validation
   before_action :validate_refs!
 
+  before_action do
+    push_frontend_feature_flag(:compare_repo_dropdown)
+  end
+
   feature_category :source_code_management
 
   def index

app/views/projects/compare/index.html.haml

@@ -13,6 +13,15 @@
   = html_escape(_("Changes are shown as if the %{b_open}source%{b_close} revision was being merged into the %{b_open}target%{b_close} revision.")) % { b_open: '<b>'.html_safe, b_close: '</b>'.html_safe }
 
 .prepend-top-20
+  - if Feature.enabled?(:compare_repo_dropdown)
+    #js-compare-selector{ data: { project_compare_index_path: project_compare_index_path(@project),
+      refs_project_path: refs_project_path(@project),
+      params_from: params[:from], params_to: params[:to],
+      project_merge_request_path: @merge_request.present? ? project_merge_request_path(@project, @merge_request) : '',
+      create_mr_path: create_mr_button? ? create_mr_path : '',
+      project_to: { id: @project.id, name: @project.full_path }.to_json,
+      projects_from: target_projects(@project).map { |project| { id:project.id, name: project.full_path } }.to_json } }
+  - else
     #js-compare-selector{ data: { project_compare_index_path: project_compare_index_path(@project),
       refs_project_path: refs_project_path(@project),
       params_from: params[:from], params_to: params[:to],

locale/gitlab.pot

@@ -7569,12 +7569,21 @@ msgstr ""
 msgid "CompareRevisions|Filter by Git revision"
 msgstr ""
 
+msgid "CompareRevisions|Select Git revision"
+msgstr ""
+
 msgid "CompareRevisions|Select branch/tag"
 msgstr ""
 
+msgid "CompareRevisions|Select target project"
+msgstr ""
+
 msgid "CompareRevisions|Tags"
 msgstr ""
 
+msgid "CompareRevisions|There was an error while loading the branch/tag list. Please try again."
+msgstr ""
+
 msgid "CompareRevisions|There was an error while updating the branch/tag list. Please try again."
 msgstr ""
 

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

+import { GlButton } from '@gitlab/ui';
+import { shallowMount } from '@vue/test-utils';
+import CompareApp from '~/projects/compare/components/app_legacy.vue';
+import RevisionDropdown from '~/projects/compare/components/revision_dropdown_legacy.vue';
+
+jest.mock('~/lib/utils/csrf', () => ({ token: 'mock-csrf-token' }));
+
+const projectCompareIndexPath = 'some/path';
+const refsProjectPath = 'some/refs/path';
+const paramsFrom = 'master';
+const paramsTo = 'master';
+
+describe('CompareApp component', () => {
+  let wrapper;
+
+  const createComponent = (props = {}) => {
+    wrapper = shallowMount(CompareApp, {
+      propsData: {
+        projectCompareIndexPath,
+        refsProjectPath,
+        paramsFrom,
+        paramsTo,
+        projectMergeRequestPath: '',
+        createMrPath: '',
+        ...props,
+      },
+    });
+  };
+
+  afterEach(() => {
+    wrapper.destroy();
+    wrapper = null;
+  });
+
+  beforeEach(() => {
+    createComponent();
+  });
+
+  it('renders component with prop', () => {
+    expect(wrapper.props()).toEqual(
+      expect.objectContaining({
+        projectCompareIndexPath,
+        refsProjectPath,
+        paramsFrom,
+        paramsTo,
+      }),
+    );
+  });
+
+  it('contains the correct form attributes', () => {
+    expect(wrapper.attributes('action')).toBe(projectCompareIndexPath);
+    expect(wrapper.attributes('method')).toBe('POST');
+  });
+
+  it('has input with csrf token', () => {
+    expect(wrapper.find('input[name="authenticity_token"]').attributes('value')).toBe(
+      'mock-csrf-token',
+    );
+  });
+
+  it('has ellipsis', () => {
+    expect(wrapper.find('[data-testid="ellipsis"]').exists()).toBe(true);
+  });
+
+  it('render Source and Target BranchDropdown components', () => {
+    const branchDropdowns = wrapper.findAll(RevisionDropdown);
+
+    expect(branchDropdowns.length).toBe(2);
+    expect(branchDropdowns.at(0).props('revisionText')).toBe('Source');
+    expect(branchDropdowns.at(1).props('revisionText')).toBe('Target');
+  });
+
+  describe('compare button', () => {
+    const findCompareButton = () => wrapper.find(GlButton);
+
+    it('renders button', () => {
+      expect(findCompareButton().exists()).toBe(true);
+    });
+
+    it('submits form', () => {
+      findCompareButton().vm.$emit('click');
+      expect(wrapper.find('form').element.submit).toHaveBeenCalled();
+    });
+
+    it('has compare text', () => {
+      expect(findCompareButton().text()).toBe('Compare');
+    });
+  });
+
+  describe('merge request buttons', () => {
+    const findProjectMrButton = () => wrapper.find('[data-testid="projectMrButton"]');
+    const findCreateMrButton = () => wrapper.find('[data-testid="createMrButton"]');
+
+    it('does not have merge request buttons', () => {
+      createComponent();
+      expect(findProjectMrButton().exists()).toBe(false);
+      expect(findCreateMrButton().exists()).toBe(false);
+    });
+
+    it('has "View open merge request" button', () => {
+      createComponent({
+        projectMergeRequestPath: 'some/project/merge/request/path',
+      });
+      expect(findProjectMrButton().exists()).toBe(true);
+      expect(findCreateMrButton().exists()).toBe(false);
+    });
+
+    it('has "Create merge request" button', () => {
+      createComponent({
+        createMrPath: 'some/create/create/mr/path',
+      });
+      expect(findProjectMrButton().exists()).toBe(false);
+      expect(findCreateMrButton().exists()).toBe(true);
+    });
+  });
+});

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

 import { GlButton } from '@gitlab/ui';
 import { shallowMount } from '@vue/test-utils';
 import CompareApp from '~/projects/compare/components/app.vue';
-import RevisionDropdown from '~/projects/compare/components/revision_dropdown.vue';
+import RevisionCard from '~/projects/compare/components/revision_card.vue';
 
 jest.mock('~/lib/utils/csrf', () => ({ token: 'mock-csrf-token' }));
 
@@ -63,11 +63,11 @@ describe('CompareApp component', () => {
   });
 
   it('render Source and Target BranchDropdown components', () => {
-    const branchDropdowns = wrapper.findAll(RevisionDropdown);
+    const revisionCards = wrapper.findAll(RevisionCard);
 
-    expect(branchDropdowns.length).toBe(2);
-    expect(branchDropdowns.at(0).props('revisionText')).toBe('Source');
-    expect(branchDropdowns.at(1).props('revisionText')).toBe('Target');
+    expect(revisionCards.length).toBe(2);
+    expect(revisionCards.at(0).props('revisionText')).toBe('Source');
+    expect(revisionCards.at(1).props('revisionText')).toBe('Target');
   });
 
   describe('compare button', () => {

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

+import { GlDropdown } from '@gitlab/ui';
+import { shallowMount } from '@vue/test-utils';
+import RepoDropdown from '~/projects/compare/components/repo_dropdown.vue';
+
+const defaultProps = {
+  paramsName: 'to',
+};
+
+const projectToId = '1';
+const projectToName = 'some-to-name';
+const projectFromId = '2';
+const projectFromName = 'some-from-name';
+
+const defaultProvide = {
+  projectTo: { id: projectToId, name: projectToName },
+  projectsFrom: [
+    { id: projectFromId, name: projectFromName },
+    { id: 3, name: 'some-from-another-name' },
+  ],
+};
+
+describe('RepoDropdown component', () => {
+  let wrapper;
+
+  const createComponent = (props = {}, provide = {}) => {
+    wrapper = shallowMount(RepoDropdown, {
+      propsData: {
+        ...defaultProps,
+        ...props,
+      },
+      provide: {
+        ...defaultProvide,
+        ...provide,
+      },
+    });
+  };
+
+  afterEach(() => {
+    wrapper.destroy();
+    wrapper = null;
+  });
+
+  const findGlDropdown = () => wrapper.find(GlDropdown);
+  const findHiddenInput = () => wrapper.find('input[type="hidden"]');
+
+  describe('Source Revision', () => {
+    beforeEach(() => {
+      createComponent();
+    });
+
+    it('set hidden input', () => {
+      expect(findHiddenInput().attributes('value')).toBe(projectToId);
+    });
+
+    it('displays the project name in the disabled dropdown', () => {
+      expect(findGlDropdown().props('text')).toBe(projectToName);
+      expect(findGlDropdown().props('disabled')).toBe(true);
+    });
+
+    it('does not emit `changeTargetProject` event', async () => {
+      wrapper.vm.emitTargetProject('foo');
+      await wrapper.vm.$nextTick();
+      expect(wrapper.emitted('changeTargetProject')).toBeUndefined();
+    });
+  });
+
+  describe('Target Revision', () => {
+    beforeEach(() => {
+      createComponent({ paramsName: 'from' });
+    });
+
+    it('set hidden input of the first project', () => {
+      expect(findHiddenInput().attributes('value')).toBe(projectFromId);
+    });
+
+    it('displays the first project name initially in the dropdown', () => {
+      expect(findGlDropdown().props('text')).toBe(projectFromName);
+    });
+
+    it('updates the hiddin input value when onClick method is triggered', async () => {
+      const repoId = '100';
+      wrapper.vm.onClick({ id: repoId });
+      await wrapper.vm.$nextTick();
+      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.$emit('changeTargetProject', newTargetProject);
+      await wrapper.vm.$nextTick();
+      expect(wrapper.emitted('changeTargetProject')[1]).toEqual([newTargetProject]);
+    });
+  });
+});

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

+import { GlCard } from '@gitlab/ui';
+import { shallowMount } from '@vue/test-utils';
+import RepoDropdown from '~/projects/compare/components/repo_dropdown.vue';
+import RevisionCard from '~/projects/compare/components/revision_card.vue';
+import RevisionDropdown from '~/projects/compare/components/revision_dropdown.vue';
+
+const defaultProps = {
+  refsProjectPath: 'some/refs/path',
+  revisionText: 'Source',
+  paramsName: 'to',
+  paramsBranch: 'master',
+};
+
+describe('RepoDropdown component', () => {
+  let wrapper;
+
+  const createComponent = (props = {}) => {
+    wrapper = shallowMount(RevisionCard, {
+      propsData: {
+        ...defaultProps,
+        ...props,
+      },
+      stubs: {
+        GlCard,
+      },
+    });
+  };
+
+  afterEach(() => {
+    wrapper.destroy();
+    wrapper = null;
+  });
+
+  beforeEach(() => {
+    createComponent();
+  });
+
+  it('displays revision text', () => {
+    expect(wrapper.find(GlCard).text()).toContain(defaultProps.revisionText);
+  });
+
+  it('renders RepoDropdown component', () => {
+    expect(wrapper.findAll(RepoDropdown).exists()).toBe(true);
+  });
+
+  it('renders RevisionDropdown component', () => {
+    expect(wrapper.findAll(RevisionDropdown).exists()).toBe(true);
+  });
+});

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

+import { GlDropdown } from '@gitlab/ui';
+import { shallowMount } from '@vue/test-utils';
+import AxiosMockAdapter from 'axios-mock-adapter';
+import createFlash from '~/flash';
+import axios from '~/lib/utils/axios_utils';
+import RevisionDropdown from '~/projects/compare/components/revision_dropdown_legacy.vue';
+
+const defaultProps = {
+  refsProjectPath: 'some/refs/path',
+  revisionText: 'Target',
+  paramsName: 'from',
+  paramsBranch: 'master',
+};
+
+jest.mock('~/flash');
+
+describe('RevisionDropdown component', () => {
+  let wrapper;
+  let axiosMock;
+
+  const createComponent = (props = {}) => {
+    wrapper = shallowMount(RevisionDropdown, {
+      propsData: {
+        ...defaultProps,
+        ...props,
+      },
+    });
+  };
+
+  beforeEach(() => {
+    axiosMock = new AxiosMockAdapter(axios);
+  });
+
+  afterEach(() => {
+    wrapper.destroy();
+    axiosMock.restore();
+  });
+
+  const findGlDropdown = () => wrapper.find(GlDropdown);
+
+  it('sets hidden input', () => {
+    createComponent();
+    expect(wrapper.find('input[type="hidden"]').attributes('value')).toBe(
+      defaultProps.paramsBranch,
+    );
+  });
+
+  it('update the branches on success', async () => {
+    const Branches = ['branch-1', 'branch-2'];
+    const Tags = ['tag-1', 'tag-2', 'tag-3'];
+
+    axiosMock.onGet(defaultProps.refsProjectPath).replyOnce(200, {
+      Branches,
+      Tags,
+    });
+
+    createComponent();
+
+    await axios.waitForAll();
+
+    expect(wrapper.vm.branches).toEqual(Branches);
+    expect(wrapper.vm.tags).toEqual(Tags);
+  });
+
+  it('shows flash message on error', async () => {
+    axiosMock.onGet('some/invalid/path').replyOnce(404);
+
+    createComponent();
+
+    await wrapper.vm.fetchBranchesAndTags();
+    expect(createFlash).toHaveBeenCalled();
+  });
+
+  describe('GlDropdown component', () => {
+    it('renders props', () => {
+      createComponent();
+      expect(wrapper.props()).toEqual(expect.objectContaining(defaultProps));
+    });
+
+    it('display default text', () => {
+      createComponent({
+        paramsBranch: null,
+      });
+      expect(findGlDropdown().props('text')).toBe('Select branch/tag');
+    });
+
+    it('display params branch text', () => {
+      createComponent();
+      expect(findGlDropdown().props('text')).toBe(defaultProps.paramsBranch);
+    });
+  });
+});

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

@@ -7,7 +7,6 @@ import RevisionDropdown from '~/projects/compare/components/revision_dropdown.vu
 
 const defaultProps = {
   refsProjectPath: 'some/refs/path',
-  revisionText: 'Target',
   paramsName: 'from',
   paramsBranch: 'master',
 };
@@ -57,7 +56,6 @@ describe('RevisionDropdown component', () => {
     createComponent();
 
     await axios.waitForAll();
-
     expect(wrapper.vm.branches).toEqual(Branches);
     expect(wrapper.vm.tags).toEqual(Tags);
   });
@@ -71,6 +69,22 @@ describe('RevisionDropdown component', () => {
     expect(createFlash).toHaveBeenCalled();
   });
 
+  it('makes a new request when refsProjectPath is changed', async () => {
+    jest.spyOn(axios, 'get');
+
+    const newRefsProjectPath = 'new-selected-project-path';
+
+    createComponent();
+
+    wrapper.setProps({
+      ...defaultProps,
+      refsProjectPath: newRefsProjectPath,
+    });
+
+    await axios.waitForAll();
+    expect(axios.get).toHaveBeenLastCalledWith(newRefsProjectPath);
+  });
+
   describe('GlDropdown component', () => {
     it('renders props', () => {
       createComponent();