Add new Rails/DotSeparatedKeys cop

changelog/new_add_new_dot_separated_keys_cop.md

@@ -0,0 +1 @@
+* [#325](https://github.com/rubocop/rubocop-rails/pull/325): Add new `Rails/DotSeparatedKeys` cop. ([@fatkodima][])

config/default.yml

@@ -274,6 +274,12 @@ Rails/DeprecatedActiveModelErrorsMethods:
   VersionAdded: '2.14'
   VersionChanged: '<<next>>'
 
+Rails/DotSeparatedKeys:
+  Description: 'Enforces the use of dot-separated keys instead of `:scope` options in `I18n` translation methods.'
+  StyleGuide: 'https://rails.rubystyle.guide/#dot-separated-keys'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Rails/DuplicateAssociation:
   Description: "Don't repeat associations in a model."
   Enabled: pending

lib/rubocop/cop/rails/dot_separated_keys.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # Enforces the use of dot-separated locale keys instead of specifying the `:scope` option
+      # with an array or a single symbol in `I18n` translation methods.
+      # Dot-separated notation is easier to read and trace the hierarchy.
+      #
+      # @example
+      #   # bad
+      #   I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]
+      #   I18n.t :title, scope: :invitation
+      #
+      #   # good
+      #   I18n.t 'activerecord.errors.messages.record_invalid'
+      #   I18n.t :record_invalid, scope: 'activerecord.errors.messages'
+      #
+      class DotSeparatedKeys < Base
+        include RangeHelp
+        extend AutoCorrector
+
+        MSG = 'Use the dot-separated keys instead of specifying the `:scope` option.'
+        TRANSLATE_METHODS = %i[translate t].freeze
+
+        def_node_matcher :translate_with_scope?, <<~PATTERN
+          (send {nil? (const nil? :I18n)} {:translate :t} ${sym_type? str_type?}
+            (hash <$(pair (sym :scope) ${array_type? sym_type?}) ...>)
+          )
+        PATTERN
+
+        def on_send(node)
+          return unless TRANSLATE_METHODS.include?(node.method_name)
+
+          translate_with_scope?(node) do |key_node, scope_node|
+            return unless should_convert_scope?(scope_node)
+
+            add_offense(scope_node) do |corrector|
+              # Eat the comma on the left.
+              range = range_with_surrounding_space(range: scope_node.source_range, side: :left)
+              range = range_with_surrounding_comma(range, :left)
+              corrector.remove(range)
+
+              corrector.replace(key_node, new_key(key_node, scope_node))
+            end
+          end
+        end
+
+        private
+
+        def should_convert_scope?(scope_node)
+          scopes(scope_node).all?(&:basic_literal?)
+        end
+
+        def new_key(key_node, scope_node)
+          "'#{scopes(scope_node).map(&:value).join('.')}.#{key_node.value}'"
+        end
+
+        def scopes(scope_node)
+          value = scope_node.value
+
+          if value.array_type?
+            value.values
+          else
+            [value]
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -34,6 +34,7 @@
 require_relative 'rails/delegate'
 require_relative 'rails/delegate_allow_blank'
 require_relative 'rails/deprecated_active_model_errors_methods'
+require_relative 'rails/dot_separated_keys'
 require_relative 'rails/duplicate_association'
 require_relative 'rails/duplicate_scope'
 require_relative 'rails/duration_arithmetic'

spec/rubocop/cop/rails/dot_separated_keys_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::DotSeparatedKeys, :config do
+  it 'registers an offense and corrects when translating keys with convertible scopes' do
+    expect_offense(<<~RUBY)
+      I18n.t :key, scope: [:one, :two]
+                   ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      I18n.translate :key, scope: [:one, :two]
+                           ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      t :key, scope: [:one, :two]
+              ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      translate :key, scope: [:one, :two]
+                      ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      t :key, scope: [:one, :two], default: 'Not here'
+              ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      I18n.t :key, scope: ['one', :two]
+                   ^^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      I18n.t 'key', scope: [:one, :two]
+                    ^^^^^^^^^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+      I18n.t :key, scope: :one
+                   ^^^^^^^^^^^ Use the dot-separated keys instead of specifying the `:scope` option.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      I18n.t 'one.two.key'
+      I18n.translate 'one.two.key'
+      t 'one.two.key'
+      translate 'one.two.key'
+      t 'one.two.key', default: 'Not here'
+      I18n.t 'one.two.key'
+      I18n.t 'one.two.key'
+      I18n.t 'one.key'
+    RUBY
+  end
+
+  it 'does not register an offense when key is an array' do
+    expect_no_offenses(<<~RUBY)
+      t [:key1, :key2], scope: :one
+    RUBY
+  end
+
+  it 'does not register an offense when key is not a basic literal' do
+    expect_no_offenses(<<~RUBY)
+      t key1, scope: :one
+    RUBY
+  end
+
+  it 'does not register an offense when `scope` is an array containing non literals' do
+    expect_no_offenses(<<~RUBY)
+      t :key, scope: [:one, two]
+    RUBY
+  end
+
+  it 'does not register an offense when `scope` is a string' do
+    expect_no_offenses(<<~RUBY)
+      t :key, scope: 'one'
+    RUBY
+  end
+
+  it 'does not register an offense when `scope` is not a literal' do
+    expect_no_offenses(<<~RUBY)
+      t :key, scope: something
+    RUBY
+  end
+
+  it 'does not register an offense when there is no `scope`' do
+    expect_no_offenses(<<~RUBY)
+      t :key
+    RUBY
+  end
+end