Add new RuboCop Gettext/StaticIdentifier

This cop ensures that only static strings are passed to gettext
translation methods `_()`, `s_()`, `n_()`, `N_()`.

Any kind of interpolation, formatting, or concatenation is disallowed.

The following definitions are allowed:
* Local variables
* Method calls which are not mentioned above
* Constants

Generate TODOs for pending offenses in Ruby code.

.rubocop_todo/gettext/static_identifier.yml

+---
+Gettext/StaticIdentifier:
+  Details: grace period
+  Exclude:
+    - 'app/graphql/types/project_type.rb'
+    - 'app/models/integrations/apple_app_store.rb'
+    - 'app/models/integrations/confluence.rb'
+    - 'app/models/integrations/google_play.rb'
+    - 'app/services/import/fogbugz_service.rb'
+    - 'app/services/issuable_links/create_service.rb'
+    - 'app/services/issues/set_crm_contacts_service.rb'
+    - 'app/services/projects/create_from_template_service.rb'
+    - 'app/services/security/ci_configuration/base_create_service.rb'
+    - 'app/services/users/banned_user_base_service.rb'
+    - 'app/services/work_items/widgets/hierarchy_service/base_service.rb'
+    - 'ee/app/controllers/admin/licenses_controller.rb'
+    - 'ee/app/controllers/subscriptions/groups_controller.rb'
+    - 'ee/app/mailers/ee/emails/admin_notification.rb'
+    - 'ee/app/mailers/emails/namespace_storage_usage_mailer.rb'
+    - 'ee/app/models/ee/member.rb'
+    - 'ee/app/models/integrations/github.rb'
+    - 'ee/app/services/ee/projects/create_from_template_service.rb'
+    - 'ee/app/services/security/security_orchestration_policies/policy_configuration_validation_service.rb'
+    - 'ee/app/services/timebox/rollup_report_service.rb'
+    - 'ee/app/services/timebox_report_service.rb'
+    - 'ee/spec/controllers/groups/security/policies_controller_spec.rb'
+    - 'ee/spec/features/registrations/identity_verification_spec.rb'
+    - 'lib/gitlab/github_import/settings.rb'

rubocop/cop/gettext/static_identifier.rb

+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Gettext
+      # Ensure that gettext identifiers are statically defined and not
+      # interpolated, formatted, or concatenated.
+      #
+      # @example
+      #
+      #   # bad
+      #   _('Hi #{name}')
+      #   _('Hi %{name}' % { name: 'Luki' })
+      #   _(format('Hi %{name}', name: 'Luki'))
+      #
+      #   # good
+      #   _('Hi %{name}') % { name: 'Luki' }
+      #   format(_('Hi %{name}', name: 'Luki'))
+      #
+      #   # also good
+      #   var = "Hi"
+      #   _(var)
+      #   _(some_method_call)
+      #   _(CONST)
+      class StaticIdentifier < RuboCop::Cop::Base
+        MSG = 'Ensure to pass static strings to translation method `%{method_name}(...)`.'
+
+        # Number of parameters to check for translation methods.
+        PARAMETERS_TO_CHECK = {
+          _: 1,
+          s_: 1,
+          N_: 1,
+          n_: 2
+        }.freeze
+
+        # RuboCop-specific optimization for `on_send`.
+        RESTRICT_ON_SEND = PARAMETERS_TO_CHECK.keys.freeze
+
+        DENIED_METHOD_CALLS = %i[% format + concat].freeze
+
+        def on_send(node)
+          method_name = node.method_name
+          arguments = node.arguments
+
+          each_invalid_argument(method_name, arguments) do |argument_node|
+            message = format(MSG, method_name: method_name)
+
+            add_offense(argument_node || node, message: message)
+          end
+        end
+
+        private
+
+        def each_invalid_argument(method_name, argument_nodes)
+          number = PARAMETERS_TO_CHECK.fetch(method_name)
+
+          argument_nodes.take(number).each do |argument_node|
+            yield argument_node unless valid_argument?(argument_node)
+          end
+        end
+
+        def valid_argument?(node)
+          return false unless node
+
+          basic_type?(node) || multiline_string?(node) || allowed_method_call?(node)
+        end
+
+        def basic_type?(node)
+          node.str_type? || node.lvar_type? || node.const_type?
+        end
+
+        def multiline_string?(node)
+          node.dstr_type? && node.children.all?(&:str_type?)
+        end
+
+        def allowed_method_call?(node)
+          return false unless node.send_type?
+
+          !DENIED_METHOD_CALLS.include?(node.method_name) # rubocop:disable Rails/NegateInclude
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/gettext/static_identifier_spec.rb

+# frozen_string_literal: true
+
+require 'rubocop_spec_helper'
+require 'rspec-parameterized'
+
+require_relative '../../../../rubocop/cop/gettext/static_identifier'
+
+RSpec.describe RuboCop::Cop::Gettext::StaticIdentifier, feature_category: :internationalization do
+  describe '#_()' do
+    it 'does not flag correct use' do
+      expect_no_offenses(<<~'RUBY')
+        _('Hello')
+        _('Hello #{name}')
+
+        _('Hello %{name}') % { name: name }
+        format(_('Hello %{name}') % { name: name })
+
+        _('Hello' \
+          'Multiline')
+        _('Hello' \
+          'Multiline %{name}') % { name: name }
+
+        var = "Hello"
+        _(var)
+        _(method_name)
+        list.each { |item| _(item) }
+        _(CONST)
+      RUBY
+    end
+
+    it 'flags incorrect use' do
+      expect_offense(<<~'RUBY')
+        _('Hello' + ' concat')
+          ^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `_(...)`.
+        _('Hello'.concat(' concat'))
+          ^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `_(...)`.
+        _("Hello #{name}")
+          ^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `_(...)`.
+        _('Hello %{name}' % { name: name })
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `_(...)`.
+        _(format('Hello %{name}') % { name: name })
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `_(...)`.
+      RUBY
+    end
+  end
+
+  describe '#N_()' do
+    it 'does not flag correct use' do
+      expect_no_offenses(<<~'RUBY')
+        N_('Hello')
+        N_('Hello #{name}')
+        N_('Hello %{name}') % { name: name }
+        format(_('Hello %{name}') % { name: name })
+
+        N_('Hello' \
+           'Multiline')
+
+        var = "Hello"
+        N_(var)
+        N_(method_name)
+        list.each { |item| N_(item) }
+        N_(CONST)
+      RUBY
+    end
+
+    it 'flags incorrect use' do
+      expect_offense(<<~'RUBY')
+        N_('Hello' + ' concat')
+           ^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `N_(...)`.
+        N_("Hello #{name}")
+           ^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `N_(...)`.
+        N_('Hello %{name}' % { name: name })
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `N_(...)`.
+        N_('Hello' \
+           ^^^^^^^^^ Ensure to pass static strings to translation method `N_(...)`.
+           'Multiline %{name}' % { name: name })
+        N_(format('Hello %{name}') % { name: name })
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `N_(...)`.
+      RUBY
+    end
+  end
+
+  describe '#s_()' do
+    it 'does not flag correct use' do
+      expect_no_offenses(<<~'RUBY')
+        s_('World|Hello')
+        s_('World|Hello #{name}')
+        s_('World|Hello %{name}') % { name: name }
+        format(s_('World|Hello %{name}') % { name: name })
+
+        s_('World|Hello' \
+           'Multiline')
+
+        var = "Hello"
+        s_(var)
+        s_(method_name)
+        list.each { |item| s_(item) }
+        s_(CONST)
+      RUBY
+    end
+
+    it 'flags incorrect use' do
+      expect_offense(<<~'RUBY')
+        s_("World|Hello #{name}")
+           ^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `s_(...)`.
+        s_('World|Hello' + ' concat')
+           ^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `s_(...)`.
+        s_('World|Hello %{name}' % { name: name })
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `s_(...)`.
+        s_('World|Hello' \
+           ^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `s_(...)`.
+           'Multiline %{name}' % { name: name })
+        s_(format('World|Hello %{name}') % { name: name })
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `s_(...)`.
+      RUBY
+    end
+  end
+
+  describe '#n_()' do
+    it 'does not flag correct use' do
+      expect_no_offenses(<<~'RUBY')
+        n_('Hello', 'Hellos', 2)
+        n_('Hello', 'Hellos', count)
+
+        n_('Hello' ' concat', 'Hellos', 2)
+        n_('Hello', 'Hello' 's', 2)
+
+        n_('Hello %{name}', 'Hellos %{name}', 2) % { name: name }
+        format(n_('Hello %{name}', 'Hellos %{name}', count) % { name: name })
+
+        n_('Hello', 'Hellos' \
+           'Multiline', 2)
+
+        n_('Hello' \
+           'Multiline', 'Hellos', 2)
+
+        n_('Hello' \
+           'Multiline %{name}', 'Hellos %{name}', 2) % { name: name }
+
+        var = "Hello"
+        n_(var, var, 1)
+        n_(method_name, method_name, count)
+        list.each { |item| n_(item, item, 2) }
+        n_(CONST, CONST, 2)
+      RUBY
+    end
+
+    it 'flags incorrect use' do
+      expect_offense(<<~'RUBY')
+        n_('Hello' + ' concat', 'Hellos', 2)
+           ^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+        n_('Hello', 'Hello' + 's', 2)
+                    ^^^^^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+        n_("Hello #{name}", "Hellos", 2)
+           ^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+        n_('Hello %{name}' % { name: name }, 'Hellos', 2)
+           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+        n_('Hello' \
+           ^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+           'Multiline %{name}' % { name: name }, 'Hellos %{name}', 2)
+        n_('Hello', format('Hellos %{name}') % { name: name }, count)
+                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ensure to pass static strings to translation method `n_(...)`.
+      RUBY
+    end
+  end
+
+  describe 'edge cases' do
+    it 'does not flag' do
+      expect_no_offenses(<<~RUBY)
+        n_(s_('World|Hello'), s_('World|Hellos'), 2)
+      RUBY
+    end
+  end
+end