Add new Rails/RenderPlain cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#283](https://github.com/rubocop-hq/rubocop-rails/pull/283): Add new `Rails/FindById` cop. ([@fatkodima][])
+* [#276](https://github.com/rubocop-hq/rubocop-rails/pull/276): Add new `Rails/RenderPlainText` cop. ([@fatkodima][])
 * [#275](https://github.com/rubocop-hq/rubocop-rails/pull/275): Add new `Rails/MatchRoute` cop. ([@fatkodima][])
 * [#271](https://github.com/rubocop-hq/rubocop-rails/pull/271): Add new `Rails/RenderInline` cop. ([@fatkodima][])
 * [#281](https://github.com/rubocop-hq/rubocop-rails/pull/281): Add new `Rails/MailerName` cop. ([@fatkodima][])

config/default.yml

@@ -490,6 +490,14 @@ Rails/RenderInline:
   Enabled: 'pending'
   VersionAdded: '2.7'
 
+Rails/RenderPlainText:
+  Description: 'Prefer `render plain:` over `render text:`.'
+  StyleGuide: 'https://rails.rubystyle.guide/#plain-text-rendering'
+  Enabled: 'pending'
+  VersionAdded: '2.7'
+  # Convert only when `content_type` is explicitly set to `text/plain`.
+  ContentTypeCompatibility: true
+
 Rails/RequestReferer:
   Description: 'Use consistent syntax for request.referer.'
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -60,6 +60,7 @@
 * xref:cops_rails.adoc#railsrefutemethods[Rails/RefuteMethods]
 * xref:cops_rails.adoc#railsrelativedateconstant[Rails/RelativeDateConstant]
 * xref:cops_rails.adoc#railsrenderinline[Rails/RenderInline]
+* xref:cops_rails.adoc#railsrenderplaintext[Rails/RenderPlainText]
 * xref:cops_rails.adoc#railsrequestreferer[Rails/RequestReferer]
 * xref:cops_rails.adoc#railsreversiblemigration[Rails/ReversibleMigration]
 * xref:cops_rails.adoc#railssafenavigation[Rails/SafeNavigation]

docs/modules/ROOT/pages/cops_rails.adoc

@@ -2900,6 +2900,65 @@ end
 
 * https://rails.rubystyle.guide/#inline-rendering
 
+== Rails/RenderPlainText
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 2.7
+| -
+|===
+
+This cop identifies places where `render text:` can be
+replaced with `render plain:`.
+
+=== Examples
+
+[source,ruby]
+----
+# bad - explicit MIME type to `text/plain`
+render text: 'Ruby!', content_type: 'text/plain'
+
+# good - short and precise
+render plain: 'Ruby!'
+
+# good - explicit MIME type not to `text/plain`
+render text: 'Ruby!', content_type: 'text/html'
+----
+
+==== ContentTypeCompatibility: true (default)
+
+[source,ruby]
+----
+# good - sets MIME type to `text/html`
+render text: 'Ruby!'
+----
+
+==== ContentTypeCompatibility: false
+
+[source,ruby]
+----
+# bad - sets MIME type to `text/html`
+render text: 'Ruby!'
+----
+
+=== Configurable attributes
+
+|===
+| Name | Default value | Configurable values
+
+| ContentTypeCompatibility
+| `true`
+| Boolean
+|===
+
+=== References
+
+* https://rails.rubystyle.guide/#plain-text-rendering
+
 == Rails/RequestReferer
 
 |===

lib/rubocop/cop/rails/render_plain_text.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Rails
+      # This cop identifies places where `render text:` can be
+      # replaced with `render plain:`.
+      #
+      # @example
+      #   # bad - explicit MIME type to `text/plain`
+      #   render text: 'Ruby!', content_type: 'text/plain'
+      #
+      #   # good - short and precise
+      #   render plain: 'Ruby!'
+      #
+      #   # good - explicit MIME type not to `text/plain`
+      #   render text: 'Ruby!', content_type: 'text/html'
+      #
+      # @example ContentTypeCompatibility: true (default)
+      #   # good - sets MIME type to `text/html`
+      #   render text: 'Ruby!'
+      #
+      # @example ContentTypeCompatibility: false
+      #   # bad - sets MIME type to `text/html`
+      #   render text: 'Ruby!'
+      #
+      class RenderPlainText < Cop
+        MSG = 'Prefer `render plain:` over `render text:`.'
+
+        def_node_matcher :render_plain_text?, <<~PATTERN
+          (send nil? :render $(hash <$(pair (sym :text) $_) ...>))
+        PATTERN
+
+        def on_send(node)
+          render_plain_text?(node) do |options_node, _option_node, _option_value|
+            content_type_node = find_content_type(options_node)
+            add_offense(node) if compatible_content_type?(content_type_node)
+          end
+        end
+
+        def autocorrect(node)
+          render_plain_text?(node) do |options_node, option_node, option_value|
+            content_type_node = find_content_type(options_node)
+            rest_options = options_node.pairs - [option_node, content_type_node].compact
+
+            lambda do |corrector|
+              corrector.replace(
+                node,
+                replacement(rest_options, option_value)
+              )
+            end
+          end
+        end
+
+        private
+
+        def find_content_type(node)
+          node.pairs.find { |p| p.key.value.to_sym == :content_type }
+        end
+
+        def compatible_content_type?(node)
+          (node && node.value.value == 'text/plain') ||
+            (!node && !cop_config['ContentTypeCompatibility'])
+        end
+
+        def replacement(rest_options, option_value)
+          if rest_options.any?
+            "render plain: #{option_value.source}, #{rest_options.map(&:source).join(', ')}"
+          else
+            "render plain: #{option_value.source}"
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rails_cops.rb

@@ -62,6 +62,7 @@
 require_relative 'rails/refute_methods'
 require_relative 'rails/relative_date_constant'
 require_relative 'rails/render_inline'
+require_relative 'rails/render_plain_text'
 require_relative 'rails/request_referer'
 require_relative 'rails/reversible_migration'
 require_relative 'rails/safe_navigation'

spec/rubocop/cop/rails/render_plain_text_spec.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Rails::RenderPlainText, :config do
+  subject(:cop) { described_class.new(config) }
+
+  shared_examples 'checks_common_offense' do
+    it 'registers an offense and corrects when using `render text:` with `content_type: "text/plain"`' do
+      expect_offense(<<~RUBY)
+        render text: 'Ruby!', content_type: 'text/plain'
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `render plain:` over `render text:`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        render plain: 'Ruby!'
+      RUBY
+    end
+
+    it 'does not register an offense when using `render text:` with `content_type: "text/html"`' do
+      expect_no_offenses(<<~RUBY)
+        render text: 'Ruby!', content_type: 'text/html'
+      RUBY
+    end
+
+    it 'does not register an offense when using `render plain:`' do
+      expect_no_offenses(<<~RUBY)
+        render plain: 'Ruby!'
+      RUBY
+    end
+  end
+
+  context 'when ContentTypeCompatibility set to true' do
+    let(:cop_config) do
+      { 'ContentTypeCompatibility' => true }
+    end
+
+    it 'does not register an offense when using `render text:`' do
+      expect_no_offenses(<<~RUBY)
+        render text: 'Ruby!'
+      RUBY
+    end
+
+    it_behaves_like('checks_common_offense')
+  end
+
+  context 'when ContentTypeCompatibility set to false' do
+    let(:cop_config) do
+      { 'ContentTypeCompatibility' => false }
+    end
+
+    it 'registers an offense and corrects when using `render text:`' do
+      expect_offense(<<~RUBY)
+        render text: 'Ruby!'
+        ^^^^^^^^^^^^^^^^^^^^ Prefer `render plain:` over `render text:`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        render plain: 'Ruby!'
+      RUBY
+    end
+
+    it_behaves_like('checks_common_offense')
+  end
+end