WIP: Optimize the selection of applicable filterable items.

Before, we did a linear scan over the list of filterable
items (e.g. `config.include` modules), and checked if each
is applicable to a particular example or example group. This
linear scan re-performs the same work over and over again, when
you consider there may be many examples/groups that lack the same
metadata keys that would be used for inclusion.

The solution is to memoize that work. We can’t simply use the
example or group’s metadata as the memorization key, though,
as each example and group have different metadata (e.g. the
description and/or location are almost always different).
Instead, we keep track of what the applicable metadata keys are,
and we use those keys as the basis for getting a subset of
the metadata hash of just the keys we care about. We can then
use this new hash as the basis of a memoization key.

This isn’t done yet (the FilterableItemRepository still needs
specs and should handle edge cases like metadata lambdas, and
we also need to apply this to hook filtering and some other
places) but it’s far enough along that I wanted to push it up for feedback.  Some specs are failing.

Author: myronmarston

lib/rspec/core/configuration.rb

@@ -301,8 +301,8 @@ def initialize
         @start_time = $_rspec_core_load_started_at || ::RSpec::Core::Time.now
         # rubocop:enable Style/GlobalVars
         @expectation_frameworks = []
-        @include_modules = []
-        @extend_modules = []
+        @include_modules = FilterableItemRepository.new(:any?)
+        @extend_modules = FilterableItemRepository.new(:any?)
         @mock_framework = nil
         @files_or_directories_to_run = []
         @color = false
@@ -331,7 +331,7 @@ def initialize
         @profile_examples = false
         @requires = []
         @libs = []
-        @derived_metadata_blocks = []
+        @derived_metadata_blocks = FilterableItemRepository.new(:any?)
       end
 
       # @private
@@ -1050,7 +1050,7 @@ def exclusion_filter
       # @see #extend
       def include(mod, *filters)
         meta = Metadata.build_hash_from(filters, :warn_about_example_group_filtering)
-        include_modules << [mod, meta]
+        include_modules.add(mod, meta)
       end
 
       # Tells RSpec to extend example groups with `mod`. Methods defined in
@@ -1084,7 +1084,7 @@ def include(mod, *filters)
       # @see #include
       def extend(mod, *filters)
         meta = Metadata.build_hash_from(filters, :warn_about_example_group_filtering)
-        extend_modules << [mod, meta]
+        extend_modules.add(mod, meta)
       end
 
       # @private
@@ -1344,13 +1344,13 @@ def disable_monkey_patching!
       #   end
       def define_derived_metadata(*filters, &block)
         meta = Metadata.build_hash_from(filters, :warn_about_example_group_filtering)
-        @derived_metadata_blocks << [meta, block]
+        @derived_metadata_blocks.add(block, meta)
       end
 
       # @private
       def apply_derived_metadata_to(metadata)
-        @derived_metadata_blocks.each do |filter, block|
-          block.call(metadata) if filter.empty? || MetadataFilter.apply?(:any?, filter, metadata)
+        @derived_metadata_blocks.items_for(metadata).each do |block|
+          block.call(metadata)
         end
       end
 
@@ -1470,9 +1470,9 @@ def update_pattern_attr(name, value)
         @files_to_run = nil
       end
 
-      def each_applicable_module(modules, filterable)
-        modules.each do |mod, filters|
-          yield mod if filters.empty? || filterable.apply?(:any?, filters)
+      def each_applicable_module(module_repository, filterable)
+        module_repository.items_for(filterable.metadata).each do |mod|
+          yield mod
         end
       end
 

lib/rspec/core/metadata_filter.rb

@@ -86,5 +86,34 @@ def silence_metadata_example_group_deprecations
         end
       end
     end
+
+    class FilterableItemRepository
+      def initialize(predicate)
+        @applicable_metadata_keys = Set.new
+        @items = []
+        @memoized_lookups = Hash.new do |hash, applicable_metadata|
+          hash[applicable_metadata] = @items.select do |(_, item_meta)|
+            item_meta.empty? || MetadataFilter.apply?(predicate, item_meta, applicable_metadata)
+          end.map { |item, _| item }
+        end
+      end
+
+      def add(item, metadata)
+        @items << [item, metadata]
+        @applicable_metadata_keys.merge(metadata.keys)
+        @memoized_lookups.clear
+      end
+
+      def items_for(metadata)
+        @memoized_lookups[applicable_metadata_from metadata]
+      end
+
+    private
+
+      def applicable_metadata_from(metadata)
+        # TODO: ensure this differentiates between `key: nil` and key missing
+        Hash[ @applicable_metadata_keys.to_a.zip(metadata.values_at(*@applicable_metadata_keys)) ]
+      end
+    end
   end
 end

spec/rspec/core/shared_example_group_spec.rb

@@ -106,9 +106,8 @@ module Core
             it "delegates include on configuration" do
               implementation = Proc.new { def bar; 'bar'; end }
               define_shared_group(:foo => :bar, &implementation)
-              a = RSpec.configuration.include_modules.first
-              expect(Class.new.send(:include, a[0]).new.bar).to eq('bar')
-              expect(a[1]).to eq(:foo => :bar)
+              a = RSpec.configuration.include_modules.items_for(:foo => :bar).first
+              expect(Class.new.send(:include, a).new.bar).to eq('bar')
             end
           end
 
@@ -122,9 +121,8 @@ module Core
             it "delegates include on configuration" do
               implementation = Proc.new { def bar; 'bar'; end }
               define_shared_group("name", :foo => :bar, &implementation)
-              a = RSpec.configuration.include_modules.first
-              expect(Class.new.send(:include, a[0]).new.bar).to eq('bar')
-              expect(a[1]).to eq(:foo => :bar)
+              a = RSpec.configuration.include_modules.items_for(:foo => :bar).first
+              expect(Class.new.send(:include, a).new.bar).to eq('bar')
             end
 
             describe "hooks for individual examples that have matching metadata" do