Merge branch 'track-ambiguous-refs' into 'master'

Optimise ExtractsRef when repository does not have ambiguous refs

See merge request gitlab-org/gitlab!38484

app/models/repository.rb

@@ -43,7 +43,7 @@ class Repository
                       gitlab_ci_yml branch_names tag_names branch_count
                       tag_count avatar exists? root_ref merged_branch_names
                       has_visible_content? issue_template_names merge_request_template_names
-                      user_defined_metrics_dashboard_paths xcode_project?).freeze
+                      user_defined_metrics_dashboard_paths xcode_project? has_ambiguous_refs?).freeze
 
   # Methods that use cache_method but only memoize the value
   MEMOIZED_CACHED_METHODS = %i(license).freeze
@@ -196,6 +196,31 @@ class Repository
     tag_exists?(ref) && branch_exists?(ref)
   end
 
+  # It's possible for a tag name to be a prefix (including slash) of a branch
+  # name, or vice versa. For instance, a tag named `foo` means we can't create a
+  # tag `foo/bar`, but we _can_ create a branch `foo/bar`.
+  #
+  # If we know a repository has no refs of this type (which is the common case)
+  # then separating refs from paths - as in ExtractsRef - can be faster.
+  #
+  # This method only checks one level deep, so only prefixes that contain no
+  # slashes are considered. If a repository has a tag `foo/bar` and a branch
+  # `foo/bar/baz`, it will return false.
+  def has_ambiguous_refs?
+    return false unless branch_names.present? && tag_names.present?
+
+    with_slash, no_slash = (branch_names + tag_names).partition { |ref| ref.include?('/') }
+
+    return false if with_slash.empty?
+
+    prefixes = no_slash.map { |ref| Regexp.escape(ref) }.join('|')
+    prefix_regex = %r{^#{prefixes}/}
+
+    with_slash.any? do |ref|
+      prefix_regex.match?(ref)
+    end
+  end
+
   def expand_ref(ref)
     if tag_exists?(ref)
       Gitlab::Git::TAG_REF_PREFIX + ref

changelogs/unreleased/track-ambiguous-refs.yml

+---
+title: Speed up commit lists and file blob pages on repositories with huge amounts
+  of branches or tags
+merge_request: 38484
+author:
+type: performance

lib/extracts_ref.rb

@@ -60,6 +60,11 @@ module ExtractsRef
         id = [id, '/'].join
       end
 
+      first_path_segment, rest = id.split('/', 2)
+
+      if use_first_path_segment?(first_path_segment)
+        pair = [first_path_segment, rest]
+      else
         valid_refs = ref_names.select { |v| id.start_with?("#{v}/") }
 
         if valid_refs.empty?
@@ -74,6 +79,7 @@ module ExtractsRef
           pair = id.partition(best_match)[1..-1]
         end
       end
+    end
 
     [
       pair[0].strip,
@@ -111,6 +117,15 @@ module ExtractsRef
 
   private
 
+  def use_first_path_segment?(ref)
+    return false unless ::Feature.enabled?(:extracts_path_optimization)
+    return false unless repository_container
+    return false if repository_container.repository.has_ambiguous_refs?
+
+    repository_container.repository.branch_names_include?(ref) ||
+      repository_container.repository.tag_names_include?(ref)
+  end
+
   # overridden in subclasses, do not remove
   def get_id
     id = [params[:id] || params[:ref]]

spec/models/repository_spec.rb

@@ -1245,6 +1245,32 @@ RSpec.describe Repository do
     end
   end
 
+  describe '#has_ambiguous_refs?' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:branch_names, :tag_names, :result) do
+      nil | nil | false
+      %w() | %w() | false
+      %w(a b) | %w() | false
+      %w() | %w(c d) | false
+      %w(a b) | %w(c d) | false
+      %w(a/b) | %w(c/d) | false
+      %w(a b) | %w(c d a/z) | true
+      %w(a b c/z) | %w(c d) | true
+      %w(a/b/z) | %w(a/b) | false # we only consider refs ambiguous before the first slash
+      %w(a/b/z) | %w(a/b a) | true
+    end
+
+    with_them do
+      it do
+        allow(repository).to receive(:branch_names).and_return(branch_names)
+        allow(repository).to receive(:tag_names).and_return(tag_names)
+
+        expect(repository.has_ambiguous_refs?).to eq(result)
+      end
+    end
+  end
+
   describe '#expand_ref' do
     let(:ref) { 'ref' }
 
@@ -1927,7 +1953,8 @@ RSpec.describe Repository do
         :issue_template_names,
         :merge_request_template_names,
         :user_defined_metrics_dashboard_paths,
-        :xcode_project?
+        :xcode_project?,
+        :has_ambiguous_refs?
       ])
 
       repository.after_change_head

spec/support/shared_examples/path_extraction_shared_examples.rb

@@ -125,6 +125,56 @@ RSpec.shared_examples 'extracts refs' do
         expect(extract_ref('release/app/v1.0.0/README.md')).to eq(
           ['release/app/v1.0.0', 'README.md'])
       end
+
+      context 'when the repository does not have ambiguous refs' do
+        before do
+          allow(container.repository).to receive(:has_ambiguous_refs?).and_return(false)
+        end
+
+        it 'does not fetch all ref names when the first path component is a ref' do
+          expect(self).not_to receive(:ref_names)
+          expect(container.repository).to receive(:branch_names_include?).with('v1.0.0').and_return(false)
+          expect(container.repository).to receive(:tag_names_include?).with('v1.0.0').and_return(true)
+
+          expect(extract_ref('v1.0.0/doc/README.md')).to eq(['v1.0.0', 'doc/README.md'])
+        end
+
+        it 'fetches all ref names when the first path component is not a ref' do
+          expect(self).to receive(:ref_names).and_call_original
+          expect(container.repository).to receive(:branch_names_include?).with('release').and_return(false)
+          expect(container.repository).to receive(:tag_names_include?).with('release').and_return(false)
+
+          expect(extract_ref('release/app/doc/README.md')).to eq(['release/app', 'doc/README.md'])
+        end
+
+        context 'when the extracts_path_optimization feature flag is disabled' do
+          before do
+            stub_feature_flags(extracts_path_optimization: false)
+          end
+
+          it 'always fetches all ref names' do
+            expect(self).to receive(:ref_names).and_call_original
+            expect(container.repository).not_to receive(:branch_names_include?)
+            expect(container.repository).not_to receive(:tag_names_include?)
+
+            expect(extract_ref('v1.0.0/doc/README.md')).to eq(['v1.0.0', 'doc/README.md'])
+          end
+        end
+      end
+
+      context 'when the repository has ambiguous refs' do
+        before do
+          allow(container.repository).to receive(:has_ambiguous_refs?).and_return(true)
+        end
+
+        it 'always fetches all ref names' do
+          expect(self).to receive(:ref_names).and_call_original
+          expect(container.repository).not_to receive(:branch_names_include?)
+          expect(container.repository).not_to receive(:tag_names_include?)
+
+          expect(extract_ref('v1.0.0/doc/README.md')).to eq(['v1.0.0', 'doc/README.md'])
+        end
+      end
     end
   end
 end