Migrate strip_trailing_whitespace to use component-local config under the hood

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 6
 
 ## main
 
+* Introduce component-local config and migrate `strip_trailing_whitespace` to use it under the hood.
+
+    *Simon Fish*
+
 * Add documentation on how ViewComponent works.
 
     *Joel Hawksley*

docs/guide/templates.md

@@ -181,14 +181,18 @@ end
 
 Code editors commonly add a trailing newline character to source files in keeping with the Unix standard. Including trailing whitespace in component templates can result in unwanted whitespace in the HTML, eg. if the component is rendered before the period at the end of a sentence.
 
-To strip trailing whitespace from component templates, use the `strip_trailing_whitespace` class method.
+To strip trailing whitespace from component templates, use the `strip_trailing_whitespace` component-local config option.
 
 ```ruby
 class MyComponent < ViewComponent::Base
   # do strip whitespace
-  strip_trailing_whitespace
+  configure_view_component do |config|
+    config.strip_trailing_whitespace = true
+  end
 
   # don't strip whitespace
-  strip_trailing_whitespace(false)
+  configure_view_component do |config|
+    config.strip_trailing_whitespace = false
+  end
 end
 ```

lib/view_component/base.rb

@@ -5,6 +5,7 @@
 require "view_component/collection"
 require "view_component/compile_cache"
 require "view_component/compiler"
+require "view_component/component_local_config"
 require "view_component/config"
 require "view_component/errors"
 require "view_component/inline_template"
@@ -38,6 +39,7 @@ def config
     include ViewComponent::Slotable
     include ViewComponent::Translatable
     include ViewComponent::WithContentHelper
+    include ViewComponent::ComponentLocalConfig
 
     RESERVED_PARAMETER = :content
     VC_INTERNAL_DEFAULT_FORMAT = :html
@@ -48,10 +50,6 @@ def config
     # For Content Security Policy nonces
     delegate :content_security_policy_nonce, to: :helpers
 
-    # Config option that strips trailing whitespace in templates before compiling them.
-    class_attribute :__vc_strip_trailing_whitespace, instance_accessor: false, instance_predicate: false
-    self.__vc_strip_trailing_whitespace = false # class_attribute:default doesn't work until Rails 5.2
-
     attr_accessor :__vc_original_view_context
 
     # Components render in their own view context. Helpers and other functionality
@@ -613,16 +611,38 @@ def with_collection_parameter(parameter)
       # end
       # ```
       #
+      # @deprecated Use the new component-local configuration option instead.
+      #
+      #   ```ruby
+      #   class MyComponent < ViewComponent::Base
+      #     configure_view_component do |config|
+      #       config.strip_trailing_whitespace = true
+      #     end
+      #   end
+      #   ```
+      #
       # @param value [Boolean] Whether to strip newlines.
       def strip_trailing_whitespace(value = true)
-        self.__vc_strip_trailing_whitespace = value
+        ViewComponent::Deprecation.deprecation_warning(
+          "strip_trailing_whitespace",
+          <<~DOC
+            Use the new component-local configuration option instead:
+
+            class #{self.class.name} < ViewComponent::Base
+              configure_view_component do |config|
+                config.strip_trailing_whitespace = #{value}
+              end
+            end
+          DOC
+        )
+        view_component_config.strip_trailing_whitespace = value
       end
 
       # Whether trailing whitespace will be stripped before compilation.
       #
       # @return [Boolean]
       def strip_trailing_whitespace?
-        __vc_strip_trailing_whitespace
+        view_component_config.strip_trailing_whitespace
       end
 
       # Ensure the component initializer accepts the

lib/view_component/component_local_config.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+module ViewComponent
+  module ComponentLocalConfig
+    class Configuration
+      def self.defaults
+        ActiveSupport::Configurable::Configuration[
+          strip_trailing_whitespace: false
+        ]
+      end
+
+      def initialize(config = defaults)
+        @config = config
+      end
+
+      delegate_missing_to :@config
+
+      def inheritable_copy
+        self.class.new(@config.inheritable_copy)
+      end
+
+      private
+
+      delegate :defaults, to: :class
+    end
+
+    extend ActiveSupport::Concern
+
+    included do
+      # :nocov:
+      def view_component_config
+        @__vc_config ||= self.class.view_component_config.inheritable_copy
+      end
+
+      private
+
+      def inherited(child)
+        child.instance_variable_set(:@__vc_config, nil)
+        super
+      end
+      # :nocov:
+    end
+
+    class_methods do
+      def view_component_config
+        @__vc_config ||= if respond_to?(:superclass) && superclass.respond_to?(:view_component_config)
+          superclass.view_component_config.inheritable_copy
+        else
+          # create a new "anonymous" class that will host the compiled reader methods
+          ViewComponent::ComponentLocalConfig::Configuration.new
+        end
+      end
+
+      def configure_view_component(&block)
+        view_component_config.instance_eval(&block)
+        view_component_config.compile_methods!
+      end
+    end
+  end
+end

test/sandbox/app/components/configurable_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class ConfigurableComponent < ViewComponent::Base
+  configure_view_component do |config|
+    config.strip_trailing_whitespace = true
+  end
+end

test/sandbox/test/base_test.rb

@@ -197,4 +197,12 @@ def test_uses_module_configuration
     assert_equal "AnotherController", TestAlreadyConfigurableModule::SomeComponent.test_controller
     assert_equal "AnotherController", TestAlreadyConfiguredModule::SomeComponent.test_controller
   end
+
+  def test_component_local_config_is_inheritable
+    assert_equal false, ViewComponent::Base.view_component_config.strip_trailing_whitespace
+    # This component doesn't call configure, so it should inherit the defaults.
+    assert_equal false, AnotherComponent.view_component_config.strip_trailing_whitespace
+    # This component overrides the defaults.
+    assert_equal true, ConfigurableComponent.view_component_config.strip_trailing_whitespace
+  end
 end