getBindingIdentifiers should return params for private methods

[JLHwung]

Q	A
Fixed Issues?	t.getBindingIdentifiers does not return parameter bindings for private class methods
Patch: Bug Fix?	Y
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Also include minor tweaks around scope tracking.

Performant issue

The getBindingIdentifiers is generally slow due to heavy dynamics: it even allows monkey-patching its visitor keys: getBindingIdentifiers.keys can be modified by external plugins. In my local perf test, dropping getBindingIdentifiers.keys can achieves 10x performance boost:

baseline 16 binding identifiers in patterns: 61_364 ops/sec ±0.78% (0.016ms)
baseline 32 binding identifiers in patterns: 27_504 ops/sec ±1.76% (0.036ms)
baseline 64 binding identifiers in patterns: 11_901 ops/sec ±0.75% (0.084ms)
baseline 128 binding identifiers in patterns: 4_260 ops/sec ±1.49% (0.235ms)
current 16 binding identifiers in patterns: 422_790 ops/sec ±1.03% (0.002ms)
current 32 binding identifiers in patterns: 193_291 ops/sec ±1.5% (0.005ms)
current 64 binding identifiers in patterns: 75_164 ops/sec ±1.45% (0.013ms)
current 128 binding identifiers in patterns: 27_211 ops/sec ±1.04% (0.037ms)
current2 16 binding identifiers in patterns: 432_890 ops/sec ±1.55% (0.002ms)
current2 32 binding identifiers in patterns: 250_765 ops/sec ±0.94% (0.004ms)
current2 64 binding identifiers in patterns: 118_529 ops/sec ±1.45% (0.008ms)
current2 128 binding identifiers in patterns: 58_682 ops/sec ±1.88% (0.017ms)

current is new implementation inlining visitor keys, current2 is a new implementation based on current which returns bindings in tail-first order: so we can avoid unnecessary memcpy introduced by array.shift in

babel/packages/babel-types/src/retrievers/getBindingIdentifiers.ts

Line 43 in 804a94f

const id = search.shift();

we should reconsider whether we are going to support getBindingIdentifiers.keys in Babel 8.

[babel-bot]

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[hzoo]

nice refactor here!

[JLHwung]

The FOR_INIT_KEYS is only used here. After this PR we may even remove it in Babel 8 if nobody else is using.

[nicolo-ribaudo]

👍