Disable diff file edit button if source branch is deleted

If the merge request is merged, point the edit button gets pointed to
the target branch
if the merge request is opened or closed and the source branch
gets deleted then we disable the button with a tooltip.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/213263

app/assets/javascripts/diffs/components/edit_button.vue

 <script>
 import { GlTooltipDirective, GlDeprecatedButton } from '@gitlab/ui';
+import { __ } from '~/locale';
 import Icon from '~/vue_shared/components/icon.vue';
 
 export default {
@@ -13,7 +14,8 @@ export default {
   props: {
     editPath: {
       type: String,
-      required: true,
+      required: false,
+      default: '',
     },
     canCurrentUserFork: {
       type: Boolean,
@@ -25,6 +27,18 @@ export default {
       default: false,
     },
   },
+  computed: {
+    tooltipTitle() {
+      if (this.isDisabled) {
+        return __("Can't edit as source branch was deleted");
+      }
+
+      return __('Edit file');
+    },
+    isDisabled() {
+      return !this.editPath;
+    },
+  },
   methods: {
     handleEditClick(evt) {
       if (this.canCurrentUserFork && !this.canModifyBlob) {
@@ -37,13 +51,15 @@ export default {
 </script>
 
 <template>
+  <span v-gl-tooltip.top :title="tooltipTitle">
     <gl-deprecated-button
-    v-gl-tooltip.top
       :href="editPath"
-    :title="__('Edit file')"
-    class="js-edit-blob"
+      :disabled="isDisabled"
+      :class="{ 'cursor-not-allowed': isDisabled }"
+      class="rounded-0 js-edit-blob"
       @click.native="handleEditClick"
     >
       <icon name="pencil" />
     </gl-deprecated-button>
+  </span>
 </template>

app/assets/stylesheets/framework/buttons.scss

@@ -507,6 +507,10 @@
   opacity: 1 !important;
   cursor: default !important;
 
+  &.cursor-not-allowed {
+    cursor: not-allowed !important;
+  }
+
   i {
     color: $gl-text-color-disabled !important;
   }

app/serializers/diff_file_base_entity.rb

@@ -22,16 +22,16 @@ class DiffFileBaseEntity < Grape::Entity
   expose :edit_path, if: -> (_, options) { options[:merge_request] } do |diff_file|
     merge_request = options[:merge_request]
 
-    options = merge_request.persisted? ? { from_merge_request_iid: merge_request.iid } : {}
+    next unless merge_request.merged? || merge_request.source_branch_exists?
 
-    next unless merge_request.source_project
+    target_project, target_branch = edit_project_branch_options(merge_request)
 
     if Feature.enabled?(:web_ide_default)
-      ide_edit_path(merge_request.source_project, merge_request.source_branch, diff_file.new_path)
+      ide_edit_path(target_project, target_branch, diff_file.new_path)
     else
-      project_edit_blob_path(merge_request.source_project,
-        tree_join(merge_request.source_branch, diff_file.new_path),
-        options)
+      options = merge_request.persisted? && merge_request.source_branch_exists? && !merge_request.merged? ? { from_merge_request_iid: merge_request.iid } : {}
+
+      project_edit_blob_path(target_project, tree_join(target_branch, diff_file.new_path), options)
     end
   end
 
@@ -61,7 +61,7 @@ class DiffFileBaseEntity < Grape::Entity
     next unless diff_file.blob
 
     if merge_request&.source_project && current_user
-      can_modify_blob?(diff_file.blob, merge_request.source_project, merge_request.source_branch)
+      can_modify_blob?(diff_file.blob, merge_request.source_project, merge_request.source_branch_exists? ? merge_request.source_branch : merge_request.target_branch)
     else
       false
     end
@@ -113,4 +113,12 @@ class DiffFileBaseEntity < Grape::Entity
   def current_user
     request.current_user
   end
+
+  def edit_project_branch_options(merge_request)
+    if merge_request.source_branch_exists? && !merge_request.merged?
+      [merge_request.source_project, merge_request.source_branch]
+    else
+      [merge_request.target_project, merge_request.target_branch]
+    end
+  end
 end

app/serializers/diffs_entity.rb

@@ -11,6 +11,10 @@ class DiffsEntity < Grape::Entity
     merge_request&.source_branch
   end
 
+  expose :source_branch_exists do |diffs|
+    merge_request&.source_branch_exists?
+  end
+
   expose :target_branch_name do |diffs|
     merge_request&.target_branch
   end

locale/gitlab.pot

@@ -3548,6 +3548,9 @@ msgstr ""
 msgid "Can override approvers and approvals required per merge request"
 msgstr ""
 
+msgid "Can't edit as source branch was deleted"
+msgstr ""
+
 msgid "Can't find HEAD commit for this branch"
 msgstr ""
 

spec/frontend/diffs/components/edit_button_spec.js

 import { shallowMount } from '@vue/test-utils';
+import { GlDeprecatedButton } from '@gitlab/ui';
 import EditButton from '~/diffs/components/edit_button.vue';
 
 const editPath = 'test-path';
@@ -22,7 +23,7 @@ describe('EditButton', () => {
       canCurrentUserFork: false,
     });
 
-    expect(wrapper.attributes('href')).toBe(editPath);
+    expect(wrapper.find(GlDeprecatedButton).attributes('href')).toBe(editPath);
   });
 
   it('emits a show fork message event if current user can fork', () => {
@@ -30,7 +31,7 @@ describe('EditButton', () => {
       editPath,
       canCurrentUserFork: true,
     });
-    wrapper.trigger('click');
+    wrapper.find(GlDeprecatedButton).trigger('click');
 
     return wrapper.vm.$nextTick().then(() => {
       expect(wrapper.emitted('showForkMessage')).toBeTruthy();
@@ -42,7 +43,7 @@ describe('EditButton', () => {
       editPath,
       canCurrentUserFork: false,
     });
-    wrapper.trigger('click');
+    wrapper.find(GlDeprecatedButton).trigger('click');
 
     return wrapper.vm.$nextTick().then(() => {
       expect(wrapper.emitted('showForkMessage')).toBeFalsy();
@@ -55,10 +56,20 @@ describe('EditButton', () => {
       canCurrentUserFork: true,
       canModifyBlob: true,
     });
-    wrapper.trigger('click');
+    wrapper.find(GlDeprecatedButton).trigger('click');
 
     return wrapper.vm.$nextTick().then(() => {
       expect(wrapper.emitted('showForkMessage')).toBeFalsy();
     });
   });
+
+  it('disables button if editPath is empty', () => {
+    createComponent({
+      editPath: '',
+      canCurrentUserFork: true,
+      canModifyBlob: true,
+    });
+
+    expect(wrapper.find(GlDeprecatedButton).attributes('disabled')).toBe('true');
+  });
 });

spec/serializers/diff_file_base_entity_spec.rb

@@ -34,4 +34,62 @@ describe DiffFileBaseEntity do
       expect(entity[:new_size]).to eq(132)
     end
   end
+
+  context 'edit_path' do
+    let(:diff_file) { merge_request.diffs.diff_files.to_a.last }
+    let(:options) { { request: EntityRequest.new(current_user: create(:user)), merge_request: merge_request } }
+    let(:params) { {} }
+
+    before do
+      stub_feature_flags(web_ide_default: false)
+    end
+
+    shared_examples 'a diff file edit path to the source branch' do
+      it do
+        expect(entity[:edit_path]).to eq(Gitlab::Routing.url_helpers.project_edit_blob_path(project, File.join(merge_request.source_branch, diff_file.new_path), params))
+      end
+    end
+
+    context 'open' do
+      let(:merge_request) { create(:merge_request, source_project: project, target_branch: 'master', source_branch: 'feature') }
+      let(:params) { { from_merge_request_iid: merge_request.iid } }
+
+      it_behaves_like 'a diff file edit path to the source branch'
+
+      context 'removed source branch' do
+        before do
+          allow(merge_request).to receive(:source_branch_exists?).and_return(false)
+        end
+
+        it do
+          expect(entity[:edit_path]).to eq(nil)
+        end
+      end
+    end
+
+    context 'closed' do
+      let(:merge_request) { create(:merge_request, source_project: project, state: :closed, target_branch: 'master', source_branch: 'feature') }
+      let(:params) { { from_merge_request_iid: merge_request.iid } }
+
+      it_behaves_like 'a diff file edit path to the source branch'
+
+      context 'removed source branch' do
+        before do
+          allow(merge_request).to receive(:source_branch_exists?).and_return(false)
+        end
+
+        it do
+          expect(entity[:edit_path]).to eq(nil)
+        end
+      end
+    end
+
+    context 'merged' do
+      let(:merge_request) { create(:merge_request, source_project: project, state: :merged) }
+
+      it do
+        expect(entity[:edit_path]).to eq(Gitlab::Routing.url_helpers.project_edit_blob_path(project, File.join(merge_request.target_branch, diff_file.new_path), {}))
+      end
+    end
+  end
 end

spec/serializers/diffs_metadata_entity_spec.rb

@@ -29,7 +29,7 @@ describe DiffsMetadataEntity do
         :added_lines, :removed_lines, :render_overflow_warning,
         :email_patch_path, :plain_diff_path,
         :merge_request_diffs, :context_commits,
-        :definition_path_prefix,
+        :definition_path_prefix, :source_branch_exists,
         # Attributes
         :diff_files
       )