Components with only variant template crashes the app

[sigra]

I've started to upgrade from 3.2.0 to 3.9.0 and my application stopped launching. Downgrading version by version I found that the issue starts from 3.5.0.

The app crashes with the error like:

NameError:
  undefined method `call' for class `ExampleComponent'

My component doesn't have template without variant and I sure it's an issue. Seems that Compiler#define_render_template_for expects that component class always has :call method defined:

view_component/lib/view_component/compiler.rb

Line 104 in 3487283

component_class.define_method("_call_#{safe_class_name}", component_class.instance_method(:call))

But this method isn't defined because my component has only "variant" template:

view_component/lib/view_component/compiler.rb

Lines 69 to 82 in 3487283

	templates.each do |template|
	method_name = call_method_name(template[:variant])
	redefinition_lock.synchronize do
	component_class.silence_redefinition_of_method(method_name)
	# rubocop:disable Style/EvalWithLocation
	component_class.class_eval <<-RUBY, template[:path], 0
	def #{method_name}
	#{compiled_template(template[:path])}
	end
	RUBY
	# rubocop:enable Style/EvalWithLocation
	end
	end

Steps to reproduce

1. Make a component using subdirectory template structure

app/components
├── ...
├── example_component.rb
├── example_component
|   ├── example_component.html+table.haml
├── ...

2. Run the app

System configuration

Rails version:
6.1.7.5

Ruby version:
3.2.2

Gem version:
3.5.0

[reeganviljoen]

@sigra the reason you get this error is because you aren't using a variant in your request so the component will not be rendered with a variant, and in that case it needs a default template without a variant, if you dont want the component to render without a variant, try doing a check on the variant in the render? method

[boardfish]

Thanks for the diagnosis, @reeganviljoen! Knowing this, we could start returning a helpful error here with similar advice to what you've provided just there.

[reeganviljoen]

@boardfish I can get that working when I get some time

[sigra]

Thanks for reply, @reeganviljoen . Patching the render? method didn't help. Because the error occurs earlier in the inherited block where compile method is called.

class ExampleComponent < ApplicationComponent
  def render?
    raise 'Unreachable code'
  end
end

Rails console output:

irb(main):001:0> ExampleComponent
/Users/sigra/.asdf/installs/ruby/3.2.2/lib/ruby/gems/3.2.0/gems/view_component-3.9.0/lib/view_component/compiler.rb:110:in `instance_method': undefined method `call' for class `ExampleComponent' (NameError)

      component_class.define_method(:"_call_#{safe_class_name}", component_class.instance_method(:call))
                                                                                ^^^^^^^^^^^^^^^^
Did you mean?  caller

Backtrace:

.../view_component-3.9.0/lib/view_component/compiler.rb:111:in `instance_method'
.../view_component-3.9.0/lib/view_component/compiler.rb:111:in `define_render_template_for'
.../view_component-3.9.0/lib/view_component/compiler.rb:86:in `compile'
.../view_component-3.9.0/lib/view_component/base.rb:562:in `compile'
.../view_component-3.9.0/lib/view_component/base.rb:497:in `inherited'

I know that I can create empty example_component.haml.html template and it will fix the problem. But as for me it's a little bit hacky way, because my app doesn't need to have this template. So, I assume it's a bug.

As for me the most obvious way is to check is method call defined or not by using the call_defined? method.

view_component/lib/view_component/compiler.rb

Lines 300 to 303 in c8462c2

	def call_defined?
	component_class.instance_methods(false).include?(:call) ||
	component_class.private_instance_methods(false).include?(:call)
	end

Suggested fix:

      if call_defined?
        component_class.define_method(:"_call_#{safe_class_name}", component_class.instance_method(:call))
      end

[reeganviljoen]

@sigra we really appreciate your debug samples and reproduction, this will certainly help, would you be able to write a failing test for this situation so someone can use that as a guideline to fix this bug ?

[sigra]

@reeganviljoen will be it enough? sigra@0b80539

➜  view_component git:(main) ✗ bundle exec appraisal rake

>> BUNDLE_GEMFILE=/Users/sigra/projects/view_component/gemfiles/rails_6.1.gemfile bundle exec rake
/Users/sigra/.asdf/installs/ruby/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-6.1.7.6/lib/active_support/core_ext/class/subclasses.rb:30: warning: method redefined; discarding old subclasses
/Users/sigra/projects/view_component/lib/view_component/compiler.rb:110:in `instance_method': undefined method `call' for class `VariantComponentWithoutDefaultTemplate' (NameError)

      component_class.define_method(:"_call_#{safe_class_name}", component_class.instance_method(:call))
                                                                                ^^^^^^^^^^^^^^^^
Did you mean?  caller
	from /Users/sigra/projects/view_component/lib/view_component/compiler.rb:110:in `define_render_template_for'
	from /Users/sigra/projects/view_component/lib/view_component/compiler.rb:86:in `compile'
	from /Users/sigra/projects/view_component/lib/view_component/base.rb:577:in `compile'
	from /Users/sigra/projects/view_component/lib/view_component/engine.rb:76:in `each'
	from /Users/sigra/projects/view_component/lib/view_component/engine.rb:76:in `block (2 levels) in <class:Engine>'

[reeganviljoen]

@sigra this is a big help thank you