Add after_compile hook for component extensions

[jsolas]

Following up on the conversation with @joelhawksley and @fsateler in this comment, this PR introduces a minimal extension point in the ViewComponent::Compiler.

What are you trying to accomplish?

This PR creates a minimal extension point for ViewComponent::Compiler to enable "sub-templates" functionality through a dedicated gem. The sub-templates gem will work by overriding the after_compile hook, receiving the compiled component, and then searching for additional template files (e.g., header.html.erb, row.html.erb) in the component's directory to generate corresponding call_* methods with explicit locals validation.

What approach did you choose and why?

I chose to implement a simple after_compile instance method hook as suggested by @joelhawksley. This approach is:

Simple and Direct: Following Joel's preference for simplicity over sophisticated callback systems
Easy to Document: A straightforward method override pattern that's familiar to Rails developers
Zero Overhead: No performance impact when the hook isn't overridden
Non-invasive: Doesn't modify ViewComponent's core compilation logic
Extensible: Components can easily override the method to add custom post-compilation behavior
The implementation uses allocate to call the instance method without triggering the component's constructor, avoiding the complexity of handling initialization arguments.

Anything you want to highlight for special attention from reviewers?

• The hook is implemented as an instance method (not class method) to provide maximum flexibility for extensions while avoiding Ruby inheritance edge cases
• Currently uses @component.allocate.after_compile to avoid constructor complexity, but I'm uncertain if this is the most elegant solution. Open to suggestions for alternative approaches that don't require allocate.

[joelhawksley]

After thinking about how we might write the documentation for this feature, my gut tells me that we might be better served with something simpler.

What if we instead added a no-op public after_compile method to Base and call it inside https://github.com/ViewComponent/view_component/blob/main/lib/view_component/base.rb#L539? That way, consumers could define their own after_compile that takes additional actions.

[jsolas]

The after_compile hook seems much cleaner and avoids the Rails 7.1 issues. I’ll update the PR to use that approach.

[fsateler]

Perhaps using ActiveSupport::Callbacks would make it easier to inject multiple extensions into the base gem

[jsolas]

@joelhawksley would you be open to exploring that direction, or do you prefer to keep it minimal for now?

[joelhawksley]

I'd prefer the minimal approach. I don't think we need any more complexity.

[jsolas]

@joelhawksley I've updated the PR to use the minimal after_compile approach as you suggested