750279 - (UntangleFrontEnd) [meta] Untangle front-end state

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Nicholas Nethercote [:njn] (On Long Service Leave)]

The front-end is a big ball of mud.  In particular, the state is very intertwined.  Examples:

- Parser has a pointer to TreeContext, and TreeContext has a pointer to Parser.  

- Parser.cpp includes BytecodeEmitter.h;  BytecodeEmitter.cpp includes Parser.h.

- BytecodeEmitter is a sub-class of TreeContext, but sometimes we down-cast TreeContext to BytecodeEmitter.

- The tcflags are a mish-mash of values with a range of lifetimes and mutability.  Some are set up-front and not changed;  some are set and cleared multiple times.  Some are relevant only in the parser; some are relevant in the parser and bytecode emitter.

As a result, any function that has access to any of the major pieces of front-end state -- Parser, TreeContext, BytecodeEmitter -- has access to pretty much all of it.  Speaking as someone who's only just started looking closely at the front-end, this makes things really hard to understand.

This is a tracking bug for cleaning this up.

Comment 1

[Luke Wagner [:luke]]

\o/

Comment 2

[Nicholas Nethercote [:njn] (On Long Service Leave)]

I think I'm done with this.