Strip trailing whitespace in templates

docs/CHANGELOG.md

@@ -9,6 +9,10 @@ title: Changelog
 
 ## main
 
+* Add per-component config option for stripping newlines from templates before compilation.
+
+    *Cameron Dutro*
+
 ## 2.57.1
 
 * Fix issue causing `NoMethodError`s when calling helper methods from components rendered as part of a collection.

docs/api.md

@@ -10,6 +10,18 @@ nav_order: 3
 
 ## Class methods
 
+### .strip_trailing_whitespace(value = true)
+
+Strips trailing whitespace from templates before compiling them.
+
+    class MyComponent < ViewComponent::Base
+      strip_trailing_whitespace
+    end
+
+### .strip_trailing_whitespace? → [Boolean]
+
+Whether trailing whitespace will be stripped before compilation.
+
 ### .with_collection(collection, **args)
 
 Render a component for each element in a collection ([documentation](/guide/collections)):
@@ -253,6 +265,10 @@ render_inline(MyComponent.new)
 assert_text("Hello, World!")
 ```
 
+### #rendered_component → [String]
+
+Returns the result of a render_inline call.
+
 ### #with_controller_class(klass)
 
 Set the controller to be used while executing the given block,

docs/known_issues.md

@@ -38,3 +38,19 @@ Calls to form helpers such as `form_with` in ViewComponents [don't use the defau
   <%= f.text_field :name %>
 <% end %>
 ```
+
+## Unwanted whitespace
+
+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.
+
+```ruby
+class MyComponent < ViewComponent::Base
+  # do strip whitespace
+  strip_trailing_whitespace
+
+  # don't strip whitespace
+  strip_trailing_whitespace(false)
+end
+```

lib/view_component/base.rb

@@ -31,6 +31,10 @@ class Base < ActionView::Base
     class_attribute :content_areas
     self.content_areas = [] # class_attribute:default doesn't work until Rails 5.2
 
+    # 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
@@ -539,6 +543,24 @@ def with_collection_parameter(parameter)
         @provided_collection_parameter = parameter
       end
 
+      # Strips trailing whitespace from templates before compiling them.
+      #
+      #     class MyComponent < ViewComponent::Base
+      #       strip_trailing_whitespace
+      #     end
+      #
+      # @param value [Boolean] Whether or not to strip newlines.
+      def strip_trailing_whitespace(value = true)
+        self.__vc_strip_trailing_whitespace = value
+      end
+
+      # Whether trailing whitespace will be stripped before compilation.
+      #
+      # @return [Boolean]
+      def strip_trailing_whitespace?
+        self.__vc_strip_trailing_whitespace
+      end
+
       # Ensure the component initializer accepts the
       # collection parameter. By default, we don't
       # validate that the default parameter name

lib/view_component/compiler.rb

@@ -238,6 +238,7 @@ def variants_from_inline_calls(calls)
     def compiled_template(file_path)
       handler = ActionView::Template.handler_for_extension(File.extname(file_path).gsub(".", ""))
       template = File.read(file_path)
+      template.rstrip! if component_class.strip_trailing_whitespace?
 
       if handler.method(:call).parameters.length > 1
         handler.call(component_class, template)

lib/view_component/test_helpers.rb

@@ -32,6 +32,9 @@ def refute_component_rendered
     # @private
     attr_reader :rendered_content
 
+    # Returns the result of a render_inline call.
+    #
+    # @return [String]
     def rendered_component
       ViewComponent::Deprecation.warn(
         "`rendered_component` is deprecated and will be removed in v3.0.0. " \

test/sandbox/app/components/trailing_whitespace_component.html.erb

@@ -0,0 +1 @@
+Hello, world!

test/sandbox/app/components/trailing_whitespace_component.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class TrailingWhitespaceComponent < ViewComponent::Base
+  strip_trailing_whitespace
+end

test/sandbox/test/rendering_test.rb

@@ -2,7 +2,7 @@
 
 require "test_helper"
 
-class ViewComponentTest < ViewComponent::TestCase
+class RenderingTest < ViewComponent::TestCase
   def test_render_inline
     render_inline(MyComponent.new)
 
@@ -1040,6 +1040,17 @@ def test_inherited_component_calls_super
     end
   end
 
+  def test_component_renders_without_trailing_whitespace
+    template = File.read(Rails.root.join("app/components/trailing_whitespace_component.html.erb"))
+    assert template =~ /\s+\z/, "Template does not contain any trailing whitespace"
+
+    without_template_annotations do
+      render_inline(TrailingWhitespaceComponent.new)
+    end
+
+    refute @rendered_content =~ /\s+\z/, "Rendered component contains trailing whitespace"
+  end
+
   def test_renders_objects_in_component_view_context
     not_a_component = RendersNonComponent::NotAComponent.new
     component = RendersNonComponent.new(not_a_component: not_a_component)