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Reduce regenerator helper size - #17268
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Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/59264 |
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Wow |
We run test262 tests, and now SpiderMonkey auto-syncs their tests to test262. We just need to make sure we are running |
nicolo-ribaudo
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PR: Output optimization 🔬
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| keep_fnames: mangleFns | ||
| ? noMangleFns.length | ||
| ? new RegExp(noMangleFns.join("|")) | ||
| ? new RegExp("^" + noMangleFns.join("|") + "$") |
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This should be with parentheses, otherwise ^/$ will only apply to the first/last of the options
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| return function invoke(method: "next" | "throw" | "return", arg: any) { | ||
| function invoke( | ||
| _methodName: "next" | "throw" | "return", |
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Do we need to keep the _methodName parameter here?
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It's not used, but we still keep the first argument as a string name for the sake of the shared defineIteratorMethods .
| method = _method; | ||
| arg = _arg; | ||
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| while (!done || (_ = undefined)) { |
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Does moving _ = undefined after the while make the code bigger? It seems like an optimization Terser should be able to make by itself.
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If we move it to after the while, it needs to be if (done) _ = undefined because we have a break inside the loop.
| // Call delegate.iterator[context.method](context.arg) and handle the result | ||
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| if ( | ||
| (_ = delegateIterator[FunctionNameStrings[method as 0 | 1 | 2]]) |
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We can use _methodName here and in a bunch of other places in this function.
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I tried that and it results in an error, I'll look into it again. :)
| if ( | ||
| (_ = delegateIterator[FunctionNameStrings[method as 0 | 1 | 2]]) | ||
| ) { | ||
| if ((_ = _.call(delegateIterator, arg))) { |
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Is it possible that this call re-calls one of the iterator method, causing method to be set to something different, and thus the various method checks further down break?
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Something like this maybe:
const innerIterable = {
[Symbol.iterator]() {
let i = 0;
return {
return() {
it.throw();
return this.next();
},
next() {
if (i++ < 2) return { done: false, value: "Hi 1" };
return { done: true, value: "Hi 2" };
}
};
}
};
function* gen() {
yield* innerIterable;
yield 1;
yield 2;
}
var it = gen();
console.log(it.next());
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It seems like this will throw Generator is already running. :)
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I don't get that error if I copy-paste this code in the repl for this PR and then run it: https://babeljs.io/repl/build/59215#?browsers=chrome%2058&build=&builtIns=false&corejs=false&spec=false&loose=false&code_lz=MYewdgzgLgBAlmMBTATgSSqghgIwDZIwC8MA3gFAwwDaAygJ4C2OIeAdHJillCCgLoAKAJRlKVGAVhxiMAAwBucVRRIoAVxRgxEiao1aRO3RM5soACxQgA7iKUm9azdstwIbZAA8o95RIBfABp_Km9fUQpHKjgAMxhBOABqJJgAHhgAJlF9FzIYABNwJAAuGFisPAgkIJgAN0r1UpgAIgAJGQBGFpgAh2jcrXyi5DKoFCbahrwmsvaZTJ6-0N7_ZaoA8mXyWPUwYCg4cAAqGABzJDAjKJh6OCQ8AtOEZHQuXAJ-u4eCmE6v-6PLJKTbkBooeCwEgXK7CJSgSCsJBsPAgM6JKCeJA-ERw8gIiBIlFojFsQawuFAA&forceAllTransforms=true&modules=false&shippedProposals=false&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=false&presets=env%2Cstage-2%2Cstage-3%2Ctypescript&prettier=false&targets=&version=7.27.0%2Bpr.17268&externalPlugins=&assumptions=%7B%7D
It logs twice.
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Oh, thanks! I haven't tried transformed code before.
This seems to be an existing bug, but I will try to fix it anyway.
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Oh then I would be fine with it happening in a separate PR. This PR looks good otherwise.
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We haven't run the test262 tests in I'm not sure if we should include more tests (perhaps v8) to increase confidence in this PR. |
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V8 has some in this folder: https://github.com/v8/v8/tree/main/test/mjsunit/harmony (search for "generator") |
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@liuxingbaoyu You need to rebase for CI to pass, but it seems like all the new tests are passing :) |
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One day we should figure out why on old Node.js version whenever there is a test failure then there is also that unrelated false error about |
commented
May 1, 2025
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jestjs/jest#10451 |
| toStringTagSymbol, | ||
| "GeneratorFunction", | ||
| ); | ||
| GeneratorFunction.displayName = "GeneratorFunction"; |
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Let's add an exec test for the displayName here?
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4 participants
Fixes #1, Fixes #2This looks like it would be hard to review, maybe we can use meta/regenerator#21 to reduce the risk of regression.
Although the existing tests look great.
Unfortunately after this our helpers are still much larger than TS's (2700 bytes vs 1083 bytes), but most of them are prototype definitions, which cannot be optimized away unless we decide to remove them in Babel 8.
Special thanks to TS for this PR, without their implementation I didn't even know the generator helper could be so small.
This PR still has some issues with Babel 7 compatibility, I'll fix them later.