Design: advance the timing of generating chunks and introduce draft chunks concepts

[hyfdev]

Motivation

#7 needs to transform chunks, which makes "chunks" not someting fixex but managed. The mindset of generating chunks are used to be considerd as the start of rendering output. Now it's a bit of different, generating draft chunks is a process before "generating finalized chunks", drafts chunks are designed for transform/mutating.

History

Previously the intuitive feeling about chunks is once they're generated, they're sealed. The current codebase is written with such implict mindset. But the problem is that chunks are not sealed. Multiple features show the need to mutate/transform chunks in various ways.

• chunkOptimization(this feature contains various optimization passes) will move modules from chunks to chunk and remove unnecessary ones
• inlineCommonChunks: it's the chunks that get inlined not the modules #7 takes the chunks as input, select chunks that are small, and then remove(inline) them.

All these things show the need of mutating chunks, but the current struct isn't deisnged specially for this purpose, which brings up many issues.

We need a languague that's only for the purpose of "transfoming chunks" and then pass the result to the lower passes instead of mixing up them together.

Actions

This issue is about two things:

• Advance the timing of generating chunks to link stage
• Generate chunks are called as "DraftChunk" that has multiple properties:
  • If its export signature is sealed, extended or free to be managed
  • If loading it has side effects
  • etc

Rrefs

• Bad smell: No unified abstraction for optimizaing chunks #3