Add ability to define templates that take parameters

```ruby
class TestComponent < ViewComponent::Base
  template_arguments :list, :multiple # call_list now takes a `multiple` keyword argument
  def initialize(mode:)
    @mode = mode
  end

  def call
    case @mode
    when :list
      call_list multiple: false
    when :multilist
      call_list multiple: true
    when :summary
      call_summary
    end
  end
end
```

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 * Add support for multiple templates.
 
-    *Rob Sterner*, *Joel Hawksley*
+    *Rob Sterner*, *Joel Hawksley*, *Felipe Sateler*
 
 # 2.18.1
 

README.md

@@ -417,6 +417,28 @@ class TestComponent < ViewComponent::Base
 end
 ```
 
+You can define templates that take parameters, using the `template_arguments` method.
+
+```ruby
+class TestComponent < ViewComponent::Base
+  template_arguments :list, :multiple # call_list now takes a `multiple` keyword argument
+  def initialize(mode:)
+    @mode = mode
+  end
+
+  def call
+    case @mode
+    when :list
+      call_list multiple: false
+    when :multilist
+      call_list multiple: true
+    when :summary
+      call_summary
+    end
+  end
+end
+```
+
 ### Conditional Rendering
 
 Components can implement a `#render?` method to be called after initialization to determine if the component should render.

coverage/coverage.txt

@@ -3,7 +3,7 @@ Incomplete test coverage
 --------------------------------------------------------------------------------
 
 /app/controllers/view_components_controller.rb: 98.18% (missed: 59)
-/lib/view_component/base.rb: 97.87% (missed: 178,268,296,359)
+/lib/view_component/base.rb: 98.05% (missed: 178,268,326,389)
 /lib/view_component/engine.rb: 96.43% (missed: 22,25)
 /lib/view_component/preview.rb: 94.12% (missed: 49,59,109)
 /lib/view_component/render_to_string_monkey_patch.rb: 83.33% (missed: 9)

lib/view_component/base.rb

@@ -271,26 +271,14 @@ def compile(raise_errors: false)
           end
 
         templates.each do |template|
+          method_name, method_args = method_name_and_args_for template
+
           # Remove existing compiled template methods,
           # as Ruby warns when redefining a method.
-
-          pieces = File.basename(template[:path]).split(".")
-
-          method_name =
-            # If the template matches the name of the component,
-            # set the method name with call_method_name
-            if pieces.first == name.demodulize.underscore
-              call_method_name(template[:variant])
-            # Otherwise, append the name of the template to
-            # call_method_name
-            else
-              "#{call_method_name(template[:variant])}_#{pieces.first.to_sym}"
-            end
-
           undef_method(method_name.to_sym) if instance_methods.include?(method_name.to_sym)
 
           class_eval <<-RUBY, template[:path], line_number
-            def #{method_name}
+            def #{method_name}(#{method_args.join(", ")})
               @output_buffer = ActionView::OutputBuffer.new
               #{compiled_template(template[:path])}
             end
@@ -300,6 +288,23 @@ def #{method_name}
         CompileCache.register self
       end
 
+      # Declares arguments that need to be passed to a template.
+      #
+      # If a sidecar template needs additional locals that need to be passed
+      # at call site, then this method should be used.
+      #
+      # The signature for the resulting method will use keyword arguments
+      #
+      # @param [Symbol, String] template The template that needs arguments
+      # @param [Array<Symbol>] *args The arguments for the template
+      def template_arguments(template, *args)
+        @template_arguments ||= {}
+        template = template.to_s
+        raise ArgumentError, "Arguments already defined for template #{template}" if @template_arguments.key?(template)
+        raise ArgumentError, "Template does not exist: #{template}" if templates.none? { |t| t[:base_name].split(".").first == template }
+        @template_arguments[template] = args
+      end
+
       # we'll eventually want to update this to support other types
       def type
         "text/html"
@@ -373,6 +378,18 @@ def compiled_template(file_path)
         end
       end
 
+      def method_name_and_args_for(template)
+        pieces = template[:base_name].split(".")
+        if pieces.first == name.demodulize.underscore
+          [call_method_name(template[:variant]), []]
+        else
+          [
+            "#{call_method_name(template[:variant])}_#{pieces.first.to_sym}",
+            (@template_arguments || {}).fetch(pieces.first, []).map { |arg| "#{arg}:" }
+          ]
+        end
+      end
+
       def inline_calls
         @inline_calls ||=
           begin

test/app/components/multiple_templates_component.rb

@@ -7,12 +7,15 @@ def initialize(mode:)
     @items = ["Apple", "Banana", "Pear"]
   end
 
+  template_arguments :list, :number
+  template_arguments :summary, :string
+
   def call
     case @mode
     when :list
-      call_list
+      call_list number: 1
     when :summary
-      call_summary
+      call_summary string: "foo"
     end
   end
 end

test/app/components/multiple_templates_component/list.html.erb

@@ -1,4 +1,5 @@
 <ul>
+  <%= number %>
   <% @items.each do |item| %>
     <li><%= item %></li>
   <% end %>

test/app/components/multiple_templates_component/summary.html.erb

@@ -1 +1 @@
-<div>The items are: <%= @items.to_sentence %></div>
+<div>The items are: <%= @items.to_sentence %>, <%= string %></div>

test/view_component/base_test.rb

@@ -25,4 +25,35 @@ def test_templates_parses_all_types_of_paths
       end
     end
   end
+
+  def test_template_arguments_validates_existence
+    error = assert_raises ArgumentError do
+      Class.new(ViewComponent::Base) do
+        def self.matching_views_in_source_location
+          [
+            "/Users/fake.user/path/to.templates/component/test_component/test_component.html.erb",
+            "/Users/fake.user/path/to.templates/component/test_component/sidecar.html.erb",
+          ]
+        end
+        template_arguments :non_existing, [:foo]
+      end
+    end
+    assert_equal "Template does not exist: non_existing", error.message
+  end
+
+  def test_template_arguments_validates_duplicates
+    error = assert_raises ArgumentError do
+      Class.new(ViewComponent::Base) do
+        def self.matching_views_in_source_location
+          [
+            "/Users/fake.user/path/to.templates/component/test_component/test_component.html.erb",
+            "/Users/fake.user/path/to.templates/component/test_component/sidecar.html.erb",
+          ]
+        end
+        template_arguments :sidecar, [:foo]
+        template_arguments :sidecar, [:bar]
+      end
+    end
+    assert_equal "Arguments already defined for template sidecar", error.message
+  end
 end

test/view_component/view_component_test.rb

@@ -646,10 +646,12 @@ def test_render_multiple_templates
     assert_selector("li", text: "Apple")
     assert_selector("li", text: "Banana")
     assert_selector("li", text: "Pear")
+    assert_selector("ul", text: "1")
 
     render_inline(MultipleTemplatesComponent.new(mode: :summary))
 
     assert_selector("div", text: "Apple, Banana, and Pear")
+    assert_selector("div", text: "foo")
   end
 
   def test_renders_component_using_rails_config