Sidebar Milestone - Fix wrong URL when selecting a parent group milestone

app/assets/javascripts/milestone_select.js

@@ -56,7 +56,7 @@ export default class MilestoneSelect {
 
       if (issueUpdateURL) {
         milestoneLinkTemplate = _.template(
-          '<a href="/<%- full_path %>/milestones/<%- iid %>" class="bold has-tooltip" data-container="body" title="<%- remaining %>"><%- title %></a>',
+          '<a href="<%- web_url %>" class="bold has-tooltip" data-container="body" title="<%- remaining %>"><%- title %></a>',
         );
         milestoneLinkNoneTemplate = '<span class="no-value">None</span>';
       }

lib/api/entities.rb

@@ -412,6 +412,10 @@ module API
       expose :state, :created_at, :updated_at
       expose :due_date
       expose :start_date
+
+      expose :web_url do |milestone, _options|
+        Gitlab::UrlBuilder.build(milestone)
+      end
     end
 
     class IssueBasic < ProjectEntity

lib/gitlab/url_builder.rb

@@ -26,6 +26,8 @@ module Gitlab
         project_snippet_url(object.project, object)
       when Snippet
         snippet_url(object)
+      when Milestone
+        milestone_url(object)
       else
         raise NotImplementedError.new("No URL builder defined for #{object.class}")
       end

spec/fixtures/api/schemas/public_api/v4/milestones.json

@@ -13,7 +13,8 @@
       "created_at": { "type": "date" },
       "updated_at": { "type": "date" },
       "start_date": { "type": "date" },
-      "due_date": { "type": "date" }
+      "due_date": { "type": "date" },
+      "web_url": { "type": "string" }
     },
     "required": [
       "id", "iid", "title", "description", "state",

spec/lib/gitlab/url_builder_spec.rb

@@ -22,6 +22,31 @@ describe Gitlab::UrlBuilder do
       end
     end
 
+    context 'when passing a Milestone' do
+      let(:group) { create(:group) }
+      let(:project) { create(:project, :public, namespace: group) }
+
+      context 'belonging to a project' do
+        it 'returns a proper URL' do
+          milestone = create(:milestone, project: project)
+
+          url = described_class.build(milestone)
+
+          expect(url).to eq "#{Settings.gitlab['url']}/#{milestone.project.full_path}/milestones/#{milestone.iid}"
+        end
+      end
+
+      context 'belonging to a group' do
+        it 'returns a proper URL' do
+          milestone = create(:milestone, group: group)
+
+          url = described_class.build(milestone)
+
+          expect(url).to eq "#{Settings.gitlab['url']}/groups/#{milestone.group.full_path}/-/milestones/#{milestone.iid}"
+        end
+      end
+    end
+
     context 'when passing a MergeRequest' do
       it 'returns a proper URL' do
         merge_request = build_stubbed(:merge_request, iid: 42)