Idea: Can we cache the result of `typeToTypeNode`?

[amcasey]

A large percentage of declaration emit time (and a small percentage of check time) is spent in typeToTypeNode and tracing indicates that it is called on some types many times (hundreds or thousands in a sufficiently large project). I suspect, but have been able to demonstrate, that those requiring a import() qualification are particularly expensive. Could we cache the result? Two clear obstacles:

1. Nodes are mutated during emit, so we'd need to clone anything retrieved from the cache. I'm reasonably confident that cloning will be cheaper than recomputing.
2. typeToTypeNode takes a complex context argument. Possible workarounds include including the context hash in the cache key and storing the cached value on the context.

[amcasey]

Fixed by #43973?

[DanielRosenwasser]

Would we consider this fixed @weswigham?

[weswigham]

Maybe? The caching isn't probably as general as the OP was thinking about, but it's probably what we can get without some fairly complex (and potentially expensive) cache key manufacturing and tracking.