Merge branch 'lower-allocations-nav' into 'master'

Lower allocations when building nav

See merge request gitlab-org/gitlab!51628

app/helpers/application_helper.rb

@@ -44,7 +44,7 @@ module ApplicationHelper
   #   current_controller?('gitlab/application') # => false
   def current_controller?(*args)
     args.any? do |v|
-      v.to_s.downcase == controller.controller_name || v.to_s.downcase == controller.controller_path
+      Gitlab::Utils.safe_downcase!(v.to_s) == controller.controller_name || Gitlab::Utils.safe_downcase!(v.to_s) == controller.controller_path
     end
   end
 
@@ -59,7 +59,7 @@ module ApplicationHelper
   #   current_action?(:create)        # => false
   #   current_action?(:new, :create)  # => true
   def current_action?(*args)
-    args.any? { |v| v.to_s.downcase == action_name }
+    args.any? { |v| Gitlab::Utils.safe_downcase!(v.to_s) == action_name }
   end
 
   def admin_section?

app/helpers/tab_helper.rb

@@ -72,7 +72,8 @@ module TabHelper
     # Add our custom class into the html_options, which may or may not exist
     # and which may or may not already have a :class key
     o = options.delete(:html_options) || {}
-    o[:class] = [*o[:class], klass].join(' ').strip
+    o[:class] = [*o[:class], klass].join(' ')
+    o[:class].strip!
 
     if block_given?
       content_tag(:li, capture(&block), o)

changelogs/unreleased/lower-allocations-nav.yml

+---
+title: Lower allocations when building nav
+merge_request: 51628
+author:
+type: performance

lib/gitlab/utils.rb

@@ -174,6 +174,18 @@ module Gitlab
     rescue IPAddr::InvalidAddressError
     end
 
+    # A safe alternative to String#downcase!
+    #
+    # This will make copies of frozen strings but downcase unfrozen
+    # strings in place, reducing allocations.
+    def safe_downcase!(str)
+      if str.frozen?
+        str.downcase
+      else
+        str.downcase! || str
+      end
+    end
+
     # Converts a string to an Addressable::URI object.
     # If the string is not a valid URI, it returns nil.
     # Param uri_string should be a String object.

spec/lib/gitlab/utils_spec.rb

@@ -392,6 +392,23 @@ RSpec.describe Gitlab::Utils do
     end
   end
 
+  describe ".safe_downcase!" do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:str, :result) do
+      "test".freeze | "test"
+      "Test".freeze | "test"
+      "test" | "test"
+      "Test" | "test"
+    end
+
+    with_them do
+      it "downcases the string" do
+        expect(described_class.safe_downcase!(str)).to eq(result)
+      end
+    end
+  end
+
   describe '.parse_url' do
     it 'returns Addressable::URI object' do
       expect(described_class.parse_url('http://gitlab.com')).to be_instance_of(Addressable::URI)