Add a string methods cop

config/default.yml

@@ -636,6 +636,16 @@ Style/StringLiteralsInInterpolation:
     - single_quotes
     - double_quotes
 
+Style/StringMethods:
+  # Mapping from undesired method to desired_method
+  # e.g. to use `to_sym` over `intern`:
+  #
+  # StringMethods:
+  #   PreferredMethods:
+  #     intern: to_sym
+  PreferredMethods:
+    intern: to_sym
+
 Style/SpaceAroundBlockParameters:
   EnforcedStyleInsidePipes: no_space
   SupportedStyles:

config/enabled.yml

@@ -698,6 +698,10 @@ Style/StringLiteralsInInterpolation:
                  strings match the configured preference.
   Enabled: true
 
+Style/StringMethods:
+  Description: 'Checks if configured preferred methods are used over non-preferred.'
+  Enabled: true
+
 Style/StructInheritance:
   Description: 'Checks for inheritance from Struct.new.'
   StyleGuide: 'https://github.com/bbatsov/ruby-style-guide#no-extend-struct-new'

lib/rubocop.rb

@@ -54,6 +54,7 @@
 require 'rubocop/cop/mixin/negative_conditional'
 require 'rubocop/cop/mixin/on_method_def'
 require 'rubocop/cop/mixin/method_complexity'
+require 'rubocop/cop/mixin/method_preference'
 require 'rubocop/cop/mixin/min_body_length'
 require 'rubocop/cop/mixin/on_normal_if_unless'
 require 'rubocop/cop/mixin/parser_diagnostic'
@@ -279,6 +280,7 @@
 require 'rubocop/cop/style/special_global_vars'
 require 'rubocop/cop/style/string_literals'
 require 'rubocop/cop/style/string_literals_in_interpolation'
+require 'rubocop/cop/style/string_methods'
 require 'rubocop/cop/style/struct_inheritance'
 require 'rubocop/cop/style/symbol_array'
 require 'rubocop/cop/style/symbol_literal'

lib/rubocop/cop/mixin/method_preference.rb

@@ -0,0 +1,28 @@
+# encoding: utf-8
+
+module RuboCop
+  module Cop
+    # Common code for cops that deal with preferred methods.
+    module MethodPreference
+      def preferred_method(method)
+        preferred_methods[method.to_sym]
+      end
+
+      def preferred_methods
+        @preferred_methods ||=
+          begin
+            # Make sure default configuration 'foo' => 'bar' is removed from
+            # the total configuration if there is a 'bar' => 'foo' override.
+            default = default_cop_config['PreferredMethods']
+            merged = cop_config['PreferredMethods']
+            overrides = merged.values - default.values
+            merged.reject { |key, _| overrides.include?(key) }.symbolize_keys
+          end
+      end
+
+      def default_cop_config
+        ConfigLoader.default_configuration[cop_name]
+      end
+    end
+  end
+end

lib/rubocop/cop/style/collection_methods.rb

@@ -10,6 +10,8 @@ module Style
       # Enumerable or not (static analysis limitation), so this cop
       # can yield some false positives.
       class CollectionMethods < Cop
+        include MethodPreference
+
         MSG = 'Prefer `%s` over `%s`.'
 
         def on_block(node)
@@ -44,26 +46,6 @@ def check_method_node(node)
                              method_name)
                      )
         end
-
-        def preferred_method(method)
-          preferred_methods[method.to_sym]
-        end
-
-        def preferred_methods
-          @preferred_methods ||=
-            begin
-              # Make sure default configuration 'foo' => 'bar' is removed from
-              # the total configuration if there is a 'bar' => 'foo' override.
-              default = default_cop_config['PreferredMethods']
-              merged = cop_config['PreferredMethods']
-              overrides = merged.values - default.values
-              merged.reject { |key, _| overrides.include?(key) }.symbolize_keys
-            end
-        end
-
-        def default_cop_config
-          ConfigLoader.default_configuration[cop_name]
-        end
       end
     end
   end

lib/rubocop/cop/style/string_methods.rb

@@ -0,0 +1,32 @@
+# encoding: utf-8
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop enforces the use of consistent method names
+      # from the String class.
+      class StringMethods < Cop
+        include MethodPreference
+
+        MSG = 'Prefer `%s` over `%s`.'
+
+        def on_send(node)
+          _receiver, method_name, *_args = *node
+          return unless preferred_methods[method_name]
+          add_offense(node, :selector,
+                      format(MSG,
+                             preferred_method(method_name),
+                             method_name)
+                     )
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            corrector.replace(node.loc.selector,
+                              preferred_method(node.loc.selector.source))
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/style/string_methods_spec.rb

@@ -0,0 +1,24 @@
+# encoding: utf-8
+
+require 'spec_helper'
+
+RSpec.describe RuboCop::Cop::Style::StringMethods, :config do
+  cop_config = {
+    'PreferredMethods' => {
+      'intern' => 'to_sym'
+    }
+  }
+
+  subject(:cop) { described_class.new(config) }
+  let(:cop_config) { cop_config }
+
+  cop_config['PreferredMethods'].each do |method, preferred_method|
+    it "registers an offense for #{method}" do
+      inspect_source(cop, "'something'.#{method}")
+      expect(cop.offenses.size).to eq(1)
+      expect(cop.messages)
+        .to eq(["Prefer `#{preferred_method}` over `#{method}`."])
+      expect(cop.highlights).to eq(%w(intern))
+    end
+  end
+end