Add link_to_label helper

app/helpers/labels_helper.rb

 module LabelsHelper
   include ActionView::Helpers::TagHelper
 
+  # Link to a Label
+  #
+  # label   - Label object to link to
+  # project - Project object which will be used as the context for the label's
+  #           link. If omitted, defaults to `@project`, or the label's own
+  #           project.
+  # block   - An optional block that will be passed to `link_to`, forming the
+  #           body of the link element. If omitted, defaults to
+  #           `render_colored_label`.
+  #
+  # Examples:
+  #
+  #   # Allow the generated link to use the label's own project
+  #   link_to_label(label)
+  #
+  #   # Force the generated link to use @project
+  #   @project = Project.first
+  #   link_to_label(label)
+  #
+  #   # Force the generated link to use a provided project
+  #   link_to_label(label, project: Project.last)
+  #
+  #   # Customize link body with a block
+  #   link_to_label(label) { "My Custom Label Text" }
+  #
+  # Returns a String
+  def link_to_label(label, project: nil, &block)
+    project ||= @project || label.project
+    link = namespace_project_issues_path(project.namespace, project,
+                                         label_name: label.name)
+
+    if block_given?
+      link_to link, &block
+    else
+      link_to render_colored_label(label), link
+    end
+  end
+
   def project_label_names
     @project.labels.pluck(:title)
   end

app/views/projects/issues/_discussion.html.haml

@@ -30,5 +30,4 @@
           %label Labels
         .issue-show-labels
           - @issue.labels.each do |label|
-            = link_to namespace_project_issues_path(@project.namespace, @project, label_name: label.name) do
-              = render_colored_label(label)
+            = link_to_label(label)

app/views/projects/issues/_issue.html.haml

@@ -8,8 +8,7 @@
       = link_to_gfm issue.title, issue_path(issue), class: "row_title"
     .issue-labels
       - issue.labels.each do |label|
-        = link_to namespace_project_issues_path(issue.project.namespace, issue.project, label_name: label.name) do
-          = render_colored_label(label)
+        = link_to_label(label, project: issue.project)
     .pull-right.light
       - if issue.closed?
         %span

app/views/projects/labels/_label.html.haml

@@ -2,7 +2,7 @@
   = render_colored_label(label)
   .pull-right
     %strong.append-right-20
-      = link_to namespace_project_issues_path(@project.namespace, @project, label_name: label.name) do
+      = link_to_label(label) do
         = pluralize label.open_issues_count, 'open issue'
 
     - if can? current_user, :admin_label, @project

app/views/projects/merge_requests/_discussion.html.haml

@@ -27,5 +27,4 @@
           %label Labels
         .merge-request-show-labels
           - @merge_request.labels.each do |label|
-            = link_to namespace_project_merge_requests_path(@project.namespace, @project, label_name: label.name) do
-              = render_colored_label(label)
+            = link_to_label(label)

app/views/projects/merge_requests/_merge_request.html.haml

@@ -4,8 +4,7 @@
       = link_to_gfm merge_request.title, merge_request_path(merge_request), class: "row_title"
     .merge-request-labels
       - merge_request.labels.each do |label|
-        = link_to namespace_project_merge_requests_path(merge_request.project.namespace, merge_request.project, label_name: label.name) do
-          = render_colored_label(label)
+        = link_to_label(label, project: merge_request.project)
     .pull-right.light
       - if merge_request.merged?
         %span

spec/helpers/labels_helper_spec.rb

 require 'spec_helper'
 
 describe LabelsHelper do
-  it { expect(text_color_for_bg('#EEEEEE')).to eq('#333333') }
-  it { expect(text_color_for_bg('#222E2E')).to eq('#FFFFFF') }
+  describe 'link_to_label' do
+    let(:project) { create(:empty_project) }
+    let(:label)   { create(:label, project: project) }
+
+    context 'with @project set' do
+      before do
+        @project = project
+      end
+
+      it 'uses the instance variable' do
+        expect(label).not_to receive(:project)
+        link_to_label(label)
+      end
+    end
+
+    context 'without @project set' do
+      it "uses the label's project" do
+        expect(label).to receive(:project).and_return(project)
+        link_to_label(label)
+      end
+    end
+
+    context 'with a named project argument' do
+      it 'uses the provided project' do
+        arg = double('project')
+        expect(arg).to receive(:namespace).and_return('foo')
+        expect(arg).to receive(:to_param).and_return('foo')
+
+        link_to_label(label, project: arg)
+      end
+
+      it 'takes precedence over other types' do
+        @project = project
+        expect(@project).not_to receive(:namespace)
+        expect(label).not_to receive(:project)
+
+        arg = double('project', namespace: 'foo', to_param: 'foo')
+        link_to_label(label, project: arg)
+      end
+    end
+
+    context 'with block' do
+      it 'passes the block to link_to' do
+        link = link_to_label(label) { 'Foo' }
+        expect(link).to match('Foo')
+      end
+    end
+
+    context 'without block' do
+      it 'uses render_colored_label as the link content' do
+        expect(self).to receive(:render_colored_label).
+          with(label).and_return('Foo')
+        expect(link_to_label(label)).to match('Foo')
+      end
+    end
+  end
+
+  describe 'text_color_for_bg' do
+    it 'uses light text on dark backgrounds' do
+      expect(text_color_for_bg('#222E2E')).to eq('#FFFFFF')
+    end
+
+    it 'uses dark text on light backgrounds' do
+      expect(text_color_for_bg('#EEEEEE')).to eq('#333333')
+    end
+  end
 end