Add new Lint/HashCompareByIdentity cop

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#8796](https://github.com/rubocop-hq/rubocop/pull/8796): Add new `Lint/HashCompareByIdentity` cop. ([@fatkodima][])
+
 ## 0.92.0 (2020-09-25)
 
 ### New features

config/default.yml

@@ -1546,6 +1546,13 @@ Lint/FormatParameterMismatch:
   Enabled: true
   VersionAdded: '0.33'
 
+Lint/HashCompareByIdentity:
+  Description: 'Prefer using `Hash#compare_by_identity` than using `object_id` for keys.'
+  StyleGuide: '#identity-comparison'
+  Enabled: pending
+  Safe: false
+  VersionAdded: '0.93'
+
 Lint/HeredocMethodCallPosition:
   Description: >-
                  Checks for the ordering of a method call where

docs/modules/ROOT/pages/cops.adoc

@@ -216,6 +216,7 @@ In the following section you find all available cops:
 * xref:cops_lint.adoc#lintfloatcomparison[Lint/FloatComparison]
 * xref:cops_lint.adoc#lintfloatoutofrange[Lint/FloatOutOfRange]
 * xref:cops_lint.adoc#lintformatparametermismatch[Lint/FormatParameterMismatch]
+* xref:cops_lint.adoc#linthashcomparebyidentity[Lint/HashCompareByIdentity]
 * xref:cops_lint.adoc#lintheredocmethodcallposition[Lint/HeredocMethodCallPosition]
 * xref:cops_lint.adoc#lintidentitycomparison[Lint/IdentityComparison]
 * xref:cops_lint.adoc#lintimplicitstringconcatenation[Lint/ImplicitStringConcatenation]

docs/modules/ROOT/pages/cops_lint.adoc

@@ -1620,6 +1620,42 @@ format('Unnumbered format: %s and numbered: %2$s', a_value, another)
 format('Numbered format: %1$s and numbered %2$s', a_value, another)
 ----
 
+== Lint/HashCompareByIdentity
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| No
+| No
+| 0.93
+| -
+|===
+
+Prefer using `Hash#compare_by_identity` than using `object_id` for hash keys.
+
+This cop is marked as unsafe as a hash possibly can contain other keys
+besides `object_id`s.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+hash = {}
+hash[foo.object_id] = :bar
+hash.key?(baz.object_id)
+
+# good
+hash = {}.compare_by_identity
+hash[foo] = :bar
+hash.key?(baz)
+----
+
+=== References
+
+* https://rubystyle.guide#identity-comparison
+
 == Lint/HeredocMethodCallPosition
 
 |===

lib/rubocop.rb

@@ -279,6 +279,7 @@
 require_relative 'rubocop/cop/lint/float_comparison'
 require_relative 'rubocop/cop/lint/float_out_of_range'
 require_relative 'rubocop/cop/lint/format_parameter_mismatch'
+require_relative 'rubocop/cop/lint/hash_compare_by_identity'
 require_relative 'rubocop/cop/lint/heredoc_method_call_position'
 require_relative 'rubocop/cop/lint/identity_comparison'
 require_relative 'rubocop/cop/lint/implicit_string_concatenation'

lib/rubocop/cop/correctors/line_break_corrector.rb

@@ -52,8 +52,8 @@ def remove_semicolon(node, corrector)
         end
 
         def semicolon(node)
-          @semicolon ||= {}
-          @semicolon[node.object_id] ||= processed_source.tokens_within(node).find(&:semicolon?)
+          @semicolon ||= {}.compare_by_identity
+          @semicolon[node] ||= processed_source.tokens_within(node).find(&:semicolon?)
         end
       end
     end

lib/rubocop/cop/lint/hash_compare_by_identity.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # Prefer using `Hash#compare_by_identity` than using `object_id` for hash keys.
+      #
+      # This cop is marked as unsafe as a hash possibly can contain other keys
+      # besides `object_id`s.
+      #
+      # @example
+      #   # bad
+      #   hash = {}
+      #   hash[foo.object_id] = :bar
+      #   hash.key?(baz.object_id)
+      #
+      #   # good
+      #   hash = {}.compare_by_identity
+      #   hash[foo] = :bar
+      #   hash.key?(baz)
+      #
+      class HashCompareByIdentity < Base
+        RESTRICT_ON_SEND = %i[key? has_key? fetch [] []=].freeze
+
+        MSG = 'Use `Hash#compare_by_identity` instead of using `object_id` for keys.'
+
+        def_node_matcher :id_as_hash_key?, <<~PATTERN
+          (send _ {:key? :has_key? :fetch :[] :[]=} (send _ :object_id) ...)
+        PATTERN
+
+        def on_send(node)
+          add_offense(node) if id_as_hash_key?(node)
+        end
+      end
+    end
+  end
+end

lib/rubocop/result_cache.rb

@@ -209,8 +209,8 @@ def relevant_options_digest(options)
     # The external dependency checksums are cached per RuboCop team so that
     # the checksums don't need to be recomputed for each file.
     def team_checksum(team)
-      @checksum_by_team ||= {}
-      @checksum_by_team[team.object_id] ||= team.external_dependency_checksum
+      @checksum_by_team ||= {}.compare_by_identity
+      @checksum_by_team[team] ||= team.external_dependency_checksum
     end
 
     # We combine team and options into a single "context" checksum to avoid

lib/rubocop/runner.rb

@@ -324,8 +324,8 @@ def mobilize_team(processed_source)
     end
 
     def mobilized_cop_classes(config)
-      @mobilized_cop_classes ||= {}
-      @mobilized_cop_classes[config.object_id] ||= begin
+      @mobilized_cop_classes ||= {}.compare_by_identity
+      @mobilized_cop_classes[config] ||= begin
         cop_classes = Cop::Registry.all
 
         OptionsValidator.new(@options).validate_cop_options
@@ -399,8 +399,8 @@ def get_processed_source(file)
     # otherwise dormant team that can be used for config- and option-
     # level caching in ResultCache.
     def standby_team(config)
-      @team_by_config ||= {}
-      @team_by_config[config.object_id] ||=
+      @team_by_config ||= {}.compare_by_identity
+      @team_by_config[config] ||=
         Cop::Team.mobilize(mobilized_cop_classes(config), config, @options)
     end
   end

spec/rubocop/cop/lint/hash_compare_by_identity_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::HashCompareByIdentity do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense when using hash methods with `object_id` on receiver as a key' do
+    expect_offense(<<~RUBY)
+      hash.key?(foo.object_id)
+      ^^^^^^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+      hash.has_key?(foo.object_id)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+      hash[foo.object_id] = bar
+      ^^^^^^^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+      hash[foo.object_id]
+      ^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+      hash.fetch(foo.object_id, 42)
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+    RUBY
+  end
+
+  it 'registers an offense when using hash method with `object_id` as a key' do
+    expect_offense(<<~RUBY)
+      hash.key?(object_id)
+      ^^^^^^^^^^^^^^^^^^^^ Use `Hash#compare_by_identity` instead of using `object_id` for keys.
+    RUBY
+  end
+
+  it 'does not register an offense for hash methods without `object_id` as key' do
+    expect_no_offenses(<<~RUBY)
+      hash.key?(foo)
+    RUBY
+  end
+end