Merge branch 'pl-flat_map-qa' into 'master'

QA: Prefer `flat_map` over `map` + `flatten`

See merge request gitlab-org/gitlab-ce!30883

qa/qa/page/base.rb

@@ -181,11 +181,11 @@ module QA
           return ["Page class does not have views / elements defined!"]
         end
 
-        views.map(&:errors).flatten
+        views.flat_map(&:errors)
       end
 
       def self.elements
-        views.map(&:elements).flatten
+        views.flat_map(&:elements)
       end
 
       def send_keys_to_element(name, keys)

qa/qa/page/validator.rb

@@ -22,16 +22,14 @@ module QA
       end
 
       def descendants
-        @descendants ||= constants.map do |const|
+        @descendants ||= constants.flat_map do |const|
           case const
           when Class
             const if const < Page::Base
           when Module
             Page::Validator.new(const).descendants
           end
-        end
-
-        @descendants.flatten.compact
+        end.compact
       end
 
       def errors

qa/qa/scenario/test/sanity/selectors.rb

@@ -14,7 +14,7 @@ module QA
               Page::Validator.new(pages)
             end
 
-            validators.map(&:errors).flatten.tap do |errors|
+            validators.flat_map(&:errors).tap do |errors|
               break if errors.none?
 
               warn <<~EOS

qa/spec/specs/runner_spec.rb

@@ -125,9 +125,9 @@ describe QA::Specs::Runner do
     end
 
     def excluded_feature_tags_except(tag)
-      QA::Runtime::Env.supported_features.except(tag).map do |tag, _|
+      QA::Runtime::Env.supported_features.except(tag).flat_map do |tag, _|
         ['--tag', "~requires_#{tag}"]
-      end.flatten
+      end
     end
 
     def expect_rspec_runner_arguments(arguments)