docs: @defer requires the parent component also be standalone

[andy-bond]

Describe the problem that you experienced

When attempting to use @defer I found myself confused after reading the documentation: https://angular.dev/guide/defer#which-dependencies-are-defer-loadable

I had made my "target" component standalone: true and the only reference to it was inside that @defer block in the "parent" component.

I was confused as to why I wasn't seeing a bundle being generated for the component I deferred. I was given a hint by someone on my team that the parent also has to be standalone for it to @defer correctly!

I don't think the documentation is very clear that not only does the "target" component need to be standalone, but also the parent must be standalone.

Enter the URL of the topic with the problem

• https://angular.dev/guide/defer#which-dependencies-are-defer-loadable
• https://angular.dev/guide/defer#behavior-with-ngmodule

Describe what you were looking for in the documentation

Clear reasons why a chunk I expected to be @defered wasn't being split off.

Describe the actions that led you to experience the problem

• I created a standalone: true component
• I put it in an @defer block in a parent (that was declared in NgModule)
• My deferred block wasn't split into a separate chunk

Describe what you want to experience that would fix the problem

I would definitely like more clear documentation on what the requirements are to @defer a component.

Additionally, I think it would be helpful to potentially have a console warning (in dev mode) to indicate why something in an @defer block is not being split. This would be nice, but not a requirement :)

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