Create Gitlab::Danger::Helper#labels_list to reduce duplication

This is to reduce duplication so that other Danger config can use this
helper method.
Signed-off-by: Rémy Coutable <remy@rymai.me>

danger/changelog/Dangerfile

@@ -56,7 +56,7 @@ end
 
 if git.modified_files.include?("CHANGELOG.md")
   fail "**CHANGELOG.md was edited.** Please remove the additions and create a CHANGELOG entry.\n\n" +
-    format(CREATE_CHANGELOG_MESSAGE, mr_iid: gitlab.mr_json["iid"], mr_title: sanitized_mr_title, labels: changelog.presented_no_changelog_labels)
+    format(CREATE_CHANGELOG_MESSAGE, mr_iid: gitlab.mr_json["iid"], mr_title: sanitized_mr_title)
 end
 
 changelog_found = changelog.found
@@ -66,5 +66,5 @@ if changelog_found
   check_changelog_path(changelog_found)
 elsif changelog.needed?
   message "**[CHANGELOG missing](https://docs.gitlab.com/ee/development/changelog.html)**: If this merge request [doesn't need a CHANGELOG entry](https://docs.gitlab.com/ee/development/changelog.html#what-warrants-a-changelog-entry), feel free to ignore this message.\n\n" +
-          format(CREATE_CHANGELOG_MESSAGE, mr_iid: gitlab.mr_json["iid"], mr_title: sanitized_mr_title, labels: changelog.presented_no_changelog_labels)
+          format(CREATE_CHANGELOG_MESSAGE, mr_iid: gitlab.mr_json["iid"], mr_title: sanitized_mr_title)
 end

danger/specs/Dangerfile

@@ -7,14 +7,10 @@ That's OK as long as you're refactoring existing code,
 but please consider adding any of the %<labels>s labels.
 MSG
 
-def presented_no_changelog_labels
-  NO_SPECS_LABELS.map { |label| "~#{label}" }.join(', ')
-end
-
 has_app_changes = !helper.all_changed_files.grep(%r{\A(ee/)?(app|lib|db/(geo/)?(post_)?migrate)/}).empty?
 has_spec_changes = !helper.all_changed_files.grep(%r{\A(ee/)?spec/}).empty?
 new_specs_needed = (gitlab.mr_labels & NO_SPECS_LABELS).empty?
 
 if has_app_changes && !has_spec_changes && new_specs_needed
-  warn format(NO_NEW_SPEC_MESSAGE, labels: presented_no_changelog_labels), sticky: false
+  warn format(NO_NEW_SPEC_MESSAGE, labels: helper.labels_list(NO_SPECS_LABELS)), sticky: false
 end

lib/gitlab/danger/changelog.rb

@@ -14,10 +14,6 @@ module Gitlab
         @found ||= git.added_files.find { |path| path =~ %r{\A(ee/)?(changelogs/unreleased)(-ee)?/} }
       end
 
-      def presented_no_changelog_labels
-        NO_CHANGELOG_LABELS.map { |label| "~#{label}" }.join(', ')
-      end
-
       def sanitized_mr_title
         gitlab.mr_json["title"].gsub(/^WIP: */, '').gsub(/`/, '\\\`')
       end

lib/gitlab/danger/helper.rb

@@ -198,11 +198,14 @@ module Gitlab
         (labels & gitlab_helper.mr_labels) == labels
       end
 
+      def labels_list(labels, sep: ', ')
+        labels.map { |label| %Q{~"#{label}"} }.join(sep)
+      end
+
       def prepare_labels_for_mr(labels)
         return '' unless labels.any?
 
-        labels_list = labels.map { |label| %Q{~"#{label}"} }.join(' ')
-        "/label #{labels_list}"
+        "/label #{labels_list(labels, sep: ' ')}"
       end
 
       private

spec/lib/gitlab/danger/changelog_spec.rb

@@ -86,14 +86,6 @@ describe Gitlab::Danger::Changelog do
     end
   end
 
-  describe '#presented_no_changelog_labels' do
-    subject { changelog.presented_no_changelog_labels }
-
-    it 'returns the labels formatted' do
-      is_expected.to eq('~backstage, ~ci-build, ~meta')
-    end
-  end
-
   describe '#ee_changelog?' do
     subject { changelog.ee_changelog? }
 

spec/lib/gitlab/danger/helper_spec.rb

@@ -399,9 +399,28 @@ describe Gitlab::Danger::Helper do
     end
   end
 
+  describe '#labels_list' do
+    let(:labels) { ['telemetry', 'telemetry::reviewed'] }
+
+    it 'composes the labels string' do
+      expect(helper.labels_list(labels)).to eq('~"telemetry", ~"telemetry::reviewed"')
+    end
+
+    context 'when passing a separator' do
+      it 'composes the labels string with the given separator' do
+        expect(helper.labels_list(labels, sep: ' ')).to eq('~"telemetry" ~"telemetry::reviewed"')
+      end
+    end
+
+    it 'returns empty string for empty array' do
+      expect(helper.labels_list([])).to eq('')
+    end
+  end
+
   describe '#prepare_labels_for_mr' do
     it 'composes the labels string' do
       mr_labels = ['telemetry', 'telemetry::reviewed']
+
       expect(helper.prepare_labels_for_mr(mr_labels)).to eq('/label ~"telemetry" ~"telemetry::reviewed"')
     end