Placeholders/#lazy_builder is not supported for block component rendering

Well-spotted!

wim leers → credited penyaskito → .

Two observations:

1. We can't use exactly as-is, because that uses Block config entities; whereas XB uses the underlying block plugins directly. Still, exactly the same pattern can be applied! 👍
2. With one important exception (identified by @penyaskito!): block plugins whose rendering is delayed (by the use of Render API placeholders to execute #lazy_builders as late as possible) prevent emptiness checks necessary only when rendering XB previews

So, I think we'll want to do something conditional: use the current code path when previewing, use what @catch proposes for end users. That'd look roughly like what's in the attached PoC patch — but lots of details left to get right.

Thoughts?

This made me realize something else: 📌 Test coverage to prove that BlockPluginInterface cacheability + BigPipe support work when rendered via XB Active .

Let's first land 📌 Test coverage to prove that BlockPluginInterface cacheability + BigPipe support work when rendered via XB Active , which will clearly demonstrate the problem 👍