Cache `#can_be_resolved_in_ui?` git operations

app/services/merge_requests/conflicts/list_service.rb

@@ -17,15 +17,7 @@ module MergeRequests
         return @conflicts_can_be_resolved_in_ui = false unless merge_request.has_complete_diff_refs?
         return @conflicts_can_be_resolved_in_ui = false if merge_request.branch_missing?
 
-        begin
-          # Try to parse each conflict. If the MR's mergeable status hasn't been
-          # updated, ensure that we don't say there are conflicts to resolve
-          # when there are no conflict files.
-          conflicts.files.each(&:lines)
-          @conflicts_can_be_resolved_in_ui = conflicts.files.length > 0
-        rescue Gitlab::Git::CommandError, Gitlab::Git::Conflict::Parser::UnresolvableError, Gitlab::Git::Conflict::Resolver::ConflictSideMissing
-          @conflicts_can_be_resolved_in_ui = false
-        end
+        @conflicts_can_be_resolved_in_ui = conflicts.can_be_resolved_in_ui?
       end
 
       def conflicts

changelogs/unreleased/cache-refactor.yml

+---
+title: Cache MergeRequests can_be_resolved_in_ui? git operations
+merge_request: 17589
+author:
+type: performance

lib/gitlab/conflict/file_collection.rb

 module Gitlab
   module Conflict
     class FileCollection
+      include Gitlab::RepositoryCacheAdapter
+
       attr_reader :merge_request, :resolver
 
       def initialize(merge_request)
         our_commit = merge_request.source_branch_head.raw
         their_commit = merge_request.target_branch_head.raw
-        target_repo = merge_request.target_project.repository.raw
+        @target_repo = merge_request.target_project.repository
         @source_repo = merge_request.source_project.repository.raw
-        @resolver = Gitlab::Git::Conflict::Resolver.new(target_repo, our_commit.id, their_commit.id)
+        @our_commit_id = our_commit.id
+        @their_commit_id = their_commit.id
+        @resolver = Gitlab::Git::Conflict::Resolver.new(@target_repo.raw, @our_commit_id, @their_commit_id)
         @merge_request = merge_request
       end
 
@@ -30,6 +34,17 @@ module Gitlab
         end
       end
 
+      def can_be_resolved_in_ui?
+        # Try to parse each conflict. If the MR's mergeable status hasn't been
+        # updated, ensure that we don't say there are conflicts to resolve
+        # when there are no conflict files.
+        files.each(&:lines)
+        files.any?
+      rescue Gitlab::Git::CommandError, Gitlab::Git::Conflict::Parser::UnresolvableError, Gitlab::Git::Conflict::Resolver::ConflictSideMissing
+        false
+      end
+      cache_method :can_be_resolved_in_ui?
+
       def file_for_path(old_path, new_path)
         files.find { |file| file.their_path == old_path && file.our_path == new_path }
       end
@@ -56,6 +71,19 @@ Merge branch '#{merge_request.target_branch}' into '#{merge_request.source_branc
 #{conflict_filenames.join("\n")}
 EOM
       end
+
+      private
+
+      def cache
+        @cache ||= begin
+          # Use the commit ids as a namespace so if the MR branches get
+          # updated we instantiate the cache under a different namespace. That
+          # way don't have to worry about explicitly invalidating the cache
+          namespace = "#{@our_commit_id}:#{@their_commit_id}"
+
+          Gitlab::RepositoryCache.new(@target_repo, extra_namespace: namespace)
+        end
+      end
     end
   end
 end

lib/gitlab/repository_cache.rb

@@ -3,9 +3,10 @@ module Gitlab
   class RepositoryCache
     attr_reader :repository, :namespace, :backend
 
-    def initialize(repository, backend = Rails.cache)
+    def initialize(repository, extra_namespace: nil, backend: Rails.cache)
       @repository = repository
       @namespace = "#{repository.full_path}:#{repository.project.id}"
+      @namespace += ":#{extra_namespace}" if extra_namespace
       @backend = backend
     end
 

spec/lib/gitlab/conflict/file_collection_spec.rb

@@ -10,6 +10,38 @@ describe Gitlab::Conflict::FileCollection do
     end
   end
 
+  describe '#cache' do
+    it 'specifies a custom namespace with the merge request commit ids' do
+      our_commit = merge_request.source_branch_head.raw
+      their_commit = merge_request.target_branch_head.raw
+      custom_namespace = "#{our_commit.id}:#{their_commit.id}"
+
+      expect(file_collection.send(:cache).namespace).to include(custom_namespace)
+    end
+  end
+
+  describe '#can_be_resolved_in_ui?' do
+    it 'returns true if conflicts for this collection can be resolved in the UI' do
+      expect(file_collection.can_be_resolved_in_ui?).to be true
+    end
+
+    it "returns false if conflicts for this collection can't be resolved in the UI" do
+      expect(file_collection).to receive(:files).and_raise(Gitlab::Git::Conflict::Resolver::ConflictSideMissing)
+
+      expect(file_collection.can_be_resolved_in_ui?).to be false
+    end
+
+    it 'caches the result' do
+      expect(file_collection).to receive(:files).twice.and_call_original
+
+      expect(file_collection.can_be_resolved_in_ui?).to be true
+
+      expect(file_collection).not_to receive(:files)
+
+      expect(file_collection.can_be_resolved_in_ui?).to be true
+    end
+  end
+
   describe '#default_commit_message' do
     it 'matches the format of the git CLI commit message' do
       expect(file_collection.default_commit_message).to eq(<<EOM.chomp)

spec/lib/gitlab/repository_cache_spec.rb

@@ -5,11 +5,25 @@ describe Gitlab::RepositoryCache do
   let(:project) { create(:project) }
   let(:repository) { project.repository }
   let(:namespace) { "#{repository.full_path}:#{project.id}" }
-  let(:cache) { described_class.new(repository, backend) }
+  let(:cache) { described_class.new(repository, backend: backend) }
 
   describe '#cache_key' do
+    subject { cache.cache_key(:foo) }
+
     it 'includes the namespace' do
-      expect(cache.cache_key(:foo)).to eq "foo:#{namespace}"
+      expect(subject).to eq "foo:#{namespace}"
+    end
+
+    context 'with a given namespace' do
+      let(:extra_namespace) { 'my:data' }
+      let(:cache) do
+        described_class.new(repository, extra_namespace: extra_namespace,
+                                        backend: backend)
+      end
+
+      it 'includes the full namespace' do
+        expect(subject).to eq "foo:#{namespace}:#{extra_namespace}"
+      end
     end
   end