Add new Rails/JSONSymbolizeNames cop

changelog/new_json_symbolize_names_cop.md

@@ -0,0 +1 @@
+* [#1532](https://github.com/rubocop/rubocop-rails/pull/1532): Add new `Rails/JSONSymbolizeNames` cop. ([@viralpraxis][])

config/default.yml

@@ -682,6 +682,11 @@ Rails/InverseOf:
   Include:
     - '**/app/models/**/*.rb'
 
+Rails/JSONSymbolizeNames:
+  Description: 'Use `JSON.parse(json, symbolize_names: true)` instead of `JSON.parse(json).deep_symbolize_keys`.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Rails/LexicallyScopedActionFilter:
   Description: "Checks that methods specified in the filter's `only` or `except` options are explicitly defined in the class."
   StyleGuide: 'https://rails.rubystyle.guide#lexically-scoped-action-filter'

lib/rubocop/cop/rails/json_symbolize_names.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Use `JSON.parse(json, symbolize_names: true)` instead of `JSON.parse(json).deep_symbolize_keys`.
+
+      # Using `symbolize_names: true` is more efficient as it creates symbols during parsing
+      # rather than requiring a second pass through the data structure.
+
+      # @example
+      #   # bad
+      #   JSON.parse(json).deep_symbolize_keys
+      #
+      #   # good
+      #   JSON.parse(json, symbolize_names: true)
+      #
+      class JSONSymbolizeNames < Base
+        MSG = 'Use `symbolize_names` option.'
+
+        RESTRICT_ON_SEND = %i[deep_symbolize_keys].to_set.freeze
+
+        JSON_PARSING_METHOD_NAMES = %i[load_file load_file! parse parse!].to_set.freeze
+
+        # @!method deep_symbolize_keys?(node)
+        def_node_matcher :deep_symbolize_keys?, <<~PATTERN
+          (call
+            (send (const {nil? cbase} :JSON) JSON_PARSING_METHOD_NAMES ...) :deep_symbolize_keys)
+        PATTERN
+
+        def on_send(node)
+          deep_symbolize_keys?(node) do
+            add_offense(node)
+          end
+        end
+        alias on_csend on_send
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -75,6 +75,7 @@
 require_relative 'rails/index_with'
 require_relative 'rails/inquiry'
 require_relative 'rails/inverse_of'
+require_relative 'rails/json_symbolize_names'
 require_relative 'rails/lexically_scoped_action_filter'
 require_relative 'rails/link_to_blank'
 require_relative 'rails/mailer_name'

spec/rubocop/cop/rails/json_symbolize_names_spec.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::JSONSymbolizeNames, :config do
+  %i[load_file load_file! parse parse!].each do |method_name|
+    context "with `#{method_name}` method" do
+      it "registers an offense for `JSON.#{method_name}` followed by `deep_symbolize_keys`" do
+        expect_offense(<<~RUBY, method_name: method_name)
+          JSON.#{method_name}(json).deep_symbolize_keys
+          ^^^^^^{method_name}^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `symbolize_names` option.
+        RUBY
+      end
+
+      it "registers an offense for `::JSON.#{method_name}` followed by `deep_symbolize_keys`" do
+        expect_offense(<<~RUBY, method_name: method_name)
+          ::JSON.#{method_name}(json).deep_symbolize_keys
+          ^^^^^^^^{method_name}^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `symbolize_names` option.
+        RUBY
+      end
+
+      it "registers an offense for `::JSON.#{method_name}` followed by `deep_symbolize_keys` with safe navigation" do
+        expect_offense(<<~RUBY, method_name: method_name)
+          ::JSON.#{method_name}("null")&.deep_symbolize_keys
+          ^^^^^^^^{method_name}^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `symbolize_names` option.
+        RUBY
+      end
+
+      it "does not register for `JSON.#{method_name}` with `symbolize_names` option" do
+        expect_no_offenses(<<~RUBY)
+          JSON.#{method_name}(json, symbolize_names: true)
+        RUBY
+      end
+
+      it "does not register for single `JSON.#{method_name}`" do
+        expect_no_offenses(<<~RUBY)
+          JSON.#{method_name}(json)
+        RUBY
+      end
+    end
+  end
+end