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Partial application moves its arguments into the generated closure

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@cknitt 已經在處理了。

開始於 2026年10月20日。

  • #8936 來自 @cknitt —— 未關閉

評估

難度
4/5
預估耗時
3-5 天
新手友好度
25/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
停滯
技術堆疊
javascript
領域
compilers

研究方向

Start in compiler/ml/translcore.ml at transl_apply's uncurried_partial_application branch, then compare its argument handling with build_apply's protect path. Check the compiler tests for partial application, including cases with await, side effects, and yield. Done means arguments are evaluated once at the partial application site and remain valid outside the generated closure.

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描述

Partial application with ... puts the supplied arguments inside the closure it creates, instead of evaluating them first.

let add = (a, b, c) => a + b + c

let f = async p => {
  let h = add(await p, ...)
  h(1, 2) + h(3, 4)
}

compiles to

async function f(p) {
  let h = (extra, extra$1) => add(await p, extra, extra$1);
  return h(1, 2) + h(3, 4) | 0;
}

await inside a non-async arrow is a JavaScript syntax error, so the module fails to load.

The same placement also re-evaluates the argument on every call:

let g = () => {
  let h = add(next(), ...)
  h(1, 2) + h(1, 2)
}

function g() {
  let h = (extra, extra$1) => add(next(), extra, extra$1);
  return h(1, 2) + h(1, 2) | 0;
}

Here next() runs twice, once for each call of h.

When h is used only once, the optimizer inlines it and both problems disappear, which may be why this hasn't been noticed.

Expected: the arguments are evaluated once, where the partial application happens:

let arg = await p;
let h = (extra, extra$1) => add(arg, extra, extra$1);

Cause: in compiler/ml/translcore.ml, transl_apply's uncurried_partial_application branch puts the translated arguments directly into the body of the new function. The optional-argument path (build_apply) already let-binds non-trivial arguments outside the closure (protect); the ... path should do the same.

This also blocks generator functions, since a yield would be moved into the closure the same way.

Reproduced on master (8556f0ad72).

主要語言
ReScript
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