Allow cops to restrict callbacks on_send to specific method names only

CHANGELOG.md

@@ -17,6 +17,7 @@
 * [#8578](https://github.com/rubocop-hq/rubocop/pull/8578): Add `:restore_registry` context and `stub_cop_class` helper class. ([@marcandre][])
 * [#8579](https://github.com/rubocop-hq/rubocop/pull/8579): Add `Cop.documentation_url`.  ([@marcandre][])
 * [#8510](https://github.com/rubocop-hq/rubocop/pull/8510):  Add `RegexpNode#each_capture` and `parsed_tree`. ([@marcandre][])
+* [#8365](https://github.com/rubocop-hq/rubocop/pull/8365): Cops defining `on_send` can be optimized by defining the constant `RESTRICT_ON_SEND` with a list of acceptable method names. ([@marcandre][])
 
 ### Bug fixes
 

docs/modules/ROOT/pages/development.adoc

@@ -210,6 +210,9 @@ def on_send(node)
 end
 ----
 
+The `on_send` callback is the most used and can be optimized by restricting the acceptable
+method names with a constant `RESTRICT_ON_SEND`.
+
 And the final cop code will look like something like this:
 
 [source,ruby]
@@ -232,6 +235,8 @@ module RuboCop
           (send (send $(...) :empty?) :!)
         PATTERN
 
+        RESTRICT_ON_SEND = [:!].freeze # optimization: don't call `on_send` unless
+                                       # the method name is in this list
         def on_send(node)
           return unless not_empty_call?(node)
 

lib/rubocop/cop/base.rb

@@ -46,6 +46,9 @@ class Base # rubocop:disable Metrics/ClassLength
       # Consider creation API private
       InvestigationReport = Struct.new(:cop, :processed_source, :offenses, :corrector)
 
+      # List of methods names to restrict calls for `on_send` / `on_csend`
+      RESTRICT_ON_SEND = Set[].freeze
+
       # List of cops that should not try to autocorrect at the same
       # time as this cop
       #
@@ -287,6 +290,10 @@ def currently_disabled_lines
         @currently_disabled_lines ||= Set.new
       end
 
+      private_class_method def self.restrict_on_send
+        @restrict_on_send ||= self::RESTRICT_ON_SEND.to_set.freeze
+      end
+
       # Called before any investigation
       def begin_investigation(processed_source)
         @current_offenses = []

lib/rubocop/cop/commissioner.rb

@@ -7,6 +7,9 @@ module Cop
     class Commissioner
       include RuboCop::AST::Traversal
 
+      RESTRICTED_CALLBACKS = %i[on_send on_csend].freeze
+      private_constant :RESTRICTED_CALLBACKS
+
       # How a Commissioner returns the results of the investigation
       # as a list of Cop::InvestigationReport and any errors caught
       # during the investigation.
@@ -43,6 +46,7 @@ def initialize(cops, forces = [], options = {})
         @forces = forces
         @options = options
         @callbacks = Hash.new { |h, k| h[k] = cops_callbacks_for(k) }
+        @restricted_map = {}
 
         reset
       end
@@ -57,10 +61,17 @@ def initialize(cops, forces = [], options = {})
         method_name = :"on_#{node_type}"
         next unless method_defined?(method_name)
 
-        define_method(method_name) do |node|
-          trigger_responding_cops(method_name, node)
-          super(node) unless NO_CHILD_NODES.include?(node_type)
+        if RESTRICTED_CALLBACKS.include?(method_name)
+          trigger_restricted = "trigger_restricted_cops(:on_#{node_type}, node)"
         end
+
+        class_eval(<<~RUBY, __FILE__, __LINE__ + 1)
+          def on_#{node_type}(node)
+            trigger_responding_cops(:on_#{node_type}, node)
+            #{trigger_restricted}
+            #{'super(node)' unless NO_CHILD_NODES.include?(node_type)}
+          end
+        RUBY
       end
 
       # @return [InvestigationReport]
@@ -95,9 +106,35 @@ def reset
       end
 
       def cops_callbacks_for(callback)
-        @cops.select do |cop|
+        callbacks = @cops.select do |cop|
           cop.respond_to?(callback)
         end
+        if RESTRICTED_CALLBACKS.include?(callback)
+          @restricted_map[callback] = restricted_map(callbacks)
+        end
+        callbacks
+      end
+
+      def trigger_restricted_cops(event, node)
+        name = node.method_name
+        @restricted_map.fetch(event)[name]&.each do |cop|
+          with_cop_error_handling(cop, node) do
+            cop.send(event, node)
+          end
+        end
+      end
+
+      # Note: mutates `callbacks` in place
+      def restricted_map(callbacks)
+        map = {}
+        callbacks.select! do |cop|
+          restrictions = cop.class.send :restrict_on_send
+          restrictions.each do |name|
+            (map[name] ||= []) << cop
+          end
+          restrictions.empty?
+        end
+        map
       end
 
       def invoke(callback, cops, *args)

spec/rubocop/cop/commissioner_spec.rb

@@ -7,15 +7,18 @@
     end
 
     let(:report) { commissioner.investigate(processed_source) }
-    let(:cop_offenses) { [] }
-    let(:cop_report) do
-      RuboCop::Cop::Base::InvestigationReport
-        .new(nil, processed_source, cop_offenses, nil)
+    let(:cop_class) do
+      stub_const('Fake::FakeCop', Class.new(RuboCop::Cop::Base) do
+                                    def on_int(node); end
+                                    alias_method :on_def, :on_int
+                                    alias_method :on_send, :on_int
+                                    alias_method :on_csend, :on_int
+                                  end)
     end
     let(:cop) do
-      # rubocop:disable RSpec/VerifiedDoubles
-      double(RuboCop::Cop::Base, complete_investigation: cop_report).as_null_object
-      # rubocop:enable RSpec/VerifiedDoubles
+      cop_class.new.tap do |c|
+        allow(c).to receive(:complete_investigation).and_return(cop_report)
+      end
     end
     let(:cops) { [cop] }
     let(:options) { {} }
@@ -28,6 +31,15 @@ def method
       end
     RUBY
     let(:processed_source) { parse_source(source, 'file.rb') }
+    let(:cop_offenses) { [] }
+    let(:cop_report) do
+      RuboCop::Cop::Base::InvestigationReport
+        .new(nil, processed_source, cop_offenses, nil)
+    end
+
+    around do |example|
+      RuboCop::Cop::Registry.with_temporary_global { example.run }
+    end
 
     context 'when a cop reports offenses' do
       let(:cop_offenses) { [Object.new] }
@@ -42,6 +54,40 @@ def method
       offenses
     end
 
+    context 'traverses the AST with on_send / on_csend' do
+      let(:source) { 'foo; var = bar; var&.baz' }
+
+      context 'for unrestricted cops' do
+        it 'calls on_send all method calls' do
+          expect(cop).to receive(:on_send).twice
+          expect(cop).to receive(:on_csend).once
+          offenses
+        end
+      end
+
+      context 'for a restricted cop' do
+        before { stub_const("#{cop_class}::RESTRICT_ON_SEND", restrictions) }
+
+        let(:restrictions) { [:bar] }
+
+        it 'calls on_send for the right method calls' do
+          expect(cop).to receive(:on_send).once
+          expect(cop).not_to receive(:on_csend)
+          offenses
+        end
+
+        context 'on both csend and send' do
+          let(:restrictions) { %i[bar baz] }
+
+          it 'calls on_send for the right method calls' do
+            expect(cop).to receive(:on_send).once
+            expect(cop).to receive(:on_csend).once
+            offenses
+          end
+        end
+      end
+    end
+
     it 'stores all errors raised by the cops' do
       allow(cop).to receive(:on_int) { raise RuntimeError }