Extracted ProtectableDropdown to clean up Project#open_branches

Makes it clear this is only used in dropdowns, instead of cluttering up Project class. Since we only care about branch names, it is also possible to refactor out a lot of the set/reject logic.

A benchmark on Array/Set subtraction favoured using Arrays. This was with 5000 ‘branches’ and 2000 ‘protections’ to ensure a similar comparison to the commit which introduced using Set for intersection.

Comparison:
   array subtraction:      485.8 i/s
     set subtraction:      128.7 i/s - 3.78x slower

1 files changed, 26 insertions, 0 deletions

diff --git a/app/models/protectable_dropdown.rb b/app/models/protectable_dropdown.rb
new file mode 100644
index 00000000000..c9b2b213cd2
--- /dev/null
+++ b/app/models/protectable_dropdown.rb
@@ -0,0 +1,26 @@
+class ProtectableDropdown
+  def initialize(project, ref_type)
+    @project = project
+    @ref_type = ref_type
+  end
+
+  # Tags/branches which are yet to be individually protected
+  def protectable_ref_names
+    non_wildcard_protections = protections.reject(&:wildcard?)
+    refs.map(&:name) - non_wildcard_protections.map(&:name)
+  end
+
+  def hash
+    protectable_ref_names.map { |ref_name| { text: ref_name, id: ref_name, title: ref_name } }
+  end
+
+  private
+
+  def refs
+    @project.repository.public_send(@ref_type)
+  end
+
+  def protections
+    @project.public_send("protected_#{@ref_type}")
+  end
+end