[Fizz] Prepare Recursive Loop for More Types

[sebmarkbage]

This is a step towards adding support for more component types. I split out the rendering of each type of component into a renderX(...) function. These mirror the mountX(...) and updateX(...) functions in Fiber.

There's one architectural piece that I needed to work out to avoid having to duplicate all the code. Resulting in one of my famous weird subtle (arguably over-engineered) architectures.

The simplest form would be to just wrap every call frame in a try/catch and recursively go through the tree. Then spawn a new task at every point something suspends. That's most of what the algorithm already does.

However, try/catch isn't necessarily free in all environments/languages. It's called "long" jump for a reason. Also, spawning a new task needs to allocate a new object and initialize it. The case this gets particularly annoying is when the same component suspends several times - you'd create a new task for each time it suspends.

There are two particular cases where this is unnecessary. If we call through a function component, we're done. We'll never pop back up the stack again. Similarly, if we go through a Context provider (not modeled yet) at the root of a task, we won't ever pop back up to the parent context again. In those cases, we can just mutate the current task and if we suspend we pick up from where ever that task left off. Eventually we get to something like a host component though, where we need to pop back up to render the end tag. Or an array where we need to pop back up to render the sibling.

In this model we have two types of loops. The root loop that just mutates the current task, and if we suspend during this loop, we just reuse that task. For certain nested types of components we enter an inner loop. If this suspends, we spawn a new task and then restore the working state.

So far, that was already how I was modeling it before this PR. However before I was duplicating the pattern matching and component rendering logic. The new thing here is that it now reuses the same logic.

First, I switched the outer loop to be recursive instead of a while loop. This will be useful for keep the component stack on the real stack so that we can recreate it for production errors.

Then I unified the two recursive functions. They are now both destructive in that they mutate the task's current node. If something suspends, we pick up at the last node that was mutated.

Another important interesting quirk is that we don't use finally to restore context when we pop. That's so that the catch above can see what the context was at the place we threw. Instead, we restore the context in those inner catches if something threw.

[sizebot]

Comparing: 172e89b...deb8aa9

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	122.61 kB	122.61 kB	=	39.34 kB	39.34 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	129.17 kB	129.17 kB	=	41.43 kB	41.43 kB
facebook-www/ReactDOM-prod.classic.js	=	412.44 kB	412.44 kB	=	76.21 kB	76.21 kB
facebook-www/ReactDOM-prod.modern.js	=	400.49 kB	400.49 kB	=	74.33 kB	74.33 kB
facebook-www/ReactDOMForked-prod.classic.js	=	412.44 kB	412.44 kB	=	76.21 kB	76.21 kB
oss-experimental/react-server/cjs/react-server.development.js	+4.83%	37.13 kB	38.92 kB	+4.83%	9.69 kB	10.15 kB
oss-stable/react-server/cjs/react-server.development.js	+4.83%	37.13 kB	38.92 kB	+4.83%	9.69 kB	10.15 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-experimental/react-server/cjs/react-server.development.js	+4.83%	37.13 kB	38.92 kB	+4.83%	9.69 kB	10.15 kB
oss-stable/react-server/cjs/react-server.development.js	+4.83%	37.13 kB	38.92 kB	+4.83%	9.69 kB	10.15 kB
oss-experimental/react-dom/cjs/react-dom-unstable-fizz.node.development.js	+1.35%	133.13 kB	134.92 kB	+1.51%	31.87 kB	32.35 kB
oss-experimental/react-dom/cjs/react-dom-unstable-fizz.browser.development.js	+1.35%	133.18 kB	134.97 kB	+1.51%	31.97 kB	32.45 kB
oss-experimental/react-dom/umd/react-dom-unstable-fizz.browser.development.js	+1.33%	140.14 kB	142.00 kB	+1.55%	32.33 kB	32.83 kB

Generated by 🚫 dangerJS against deb8aa9

[sebmarkbage]

This is the duplication that I was aiming to get rid of. Normally I'd probably be ok duplicating this code but it's quite important that these don't go out of sync as we add new types.

[acdlite]

Clever! (But not too clever, I think!)