TS errors for draft objects with properties that are indexed using well-known symbols

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難度
3/5
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1-2 天
新手友好度
48/100
Issue 類型
缺陷
描述清晰度
基本清楚
活躍度
停滯
技術堆疊
javascript, typescript
領域
developer-experience, tooling

研究方向

先找出 Draft 和 WritableDraft 的型別定義，並比較它們如何處理知名符號屬性。使用 issue 中的 TypeScript repro 檢查屬性存取，以及將 draft 傳遞給 withFoo；完成的標準是 repro 在不變更預期 mutation 行為的情況下不產生 TS 錯誤。

由索引模型根據 Issue 內容生成。

描述

typescript

🐛 Bug Report

Draft<T> objects (at least according to TS) don't bring along any symbol-indexed properties from the original object. Is this expected? I'm not sure if this is only an issue in the TS types, or is the underlying JS draft object also missing its symbol-indexed properties?

Although well-known symbols are usually used with classes, I was able to repro the problem with a plain object too.

I'm using TS 4.1, if it matters.

FWIW, I ran into this because I was trying to call produce() with a deeply-nested object which had a Uint8Array-valued property far down in the tree. When I tried to pass the draft object to another method that expected the original type, TS complained that [Symbol.iterator] and [Symbol.toStringTag] properties that were required on Uint8Array but missing on the Draft<T> object. I'm not trying to mutate the array (that'd be #696); I'm just expecting a deep clone but (at least from TS's perspective) the symbol properties are missing.

Link to repro

import produce, { Draft } from 'immer';

const foo = {
  a() { return 42; },
  get [Symbol.toStringTag]() { return 'foo'; }
}

type Foo = typeof foo;

function withFoo(f: Foo) {
  return f[Symbol.toStringTag];
}

const ok = foo[Symbol.toStringTag];  // no error
const ok2 = withFoo(foo);  // no error

const producer = produce((draft: Draft<Foo>) => {
  draft.a();  // no error
  withFoo(draft);
  /*      ^^^^^
    Argument of type 'WritableDraft<{ a(): number; readonly [Symbol.toStringTag]: string; }>' 
    is not assignable to parameter of type '{ a(): number; readonly [Symbol.toStringTag]: string; }'.
    Property '[Symbol.toStringTag]' is missing in type 'WritableDraft<{ a(): number; 
    readonly [Symbol.toStringTag]: string; }>' but required in type 
    '{ a(): number; readonly [Symbol.toStringTag]: string; }'. (2345)
  */

  const fail = draft[Symbol.toStringTag];
  /*           ^^^^^^^^^^^^^^^^^^^^^^^^^
     Element implicitly has an 'any' type because expression of type 'symbol' can't be used
     to index type 'WritableDraft<{ a(): number; readonly [Symbol.toStringTag]: string; }>'.(7053)
  */
});

https://www.typescriptlang.org/play?#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-LaGK4nQAFJCpWCGhhpzZjPMW4IOl1wEAur1+Z1aMWMKX1P0K2nK2Sxs7xqAGJ06vV8A1G4Y1s1Z-a5m2Ge1wByoeCqACOqGAqmQHZyUcdrIYMYUcccCcnKdnJozdezy92BdccDkugAzNoAKwKExGSObgZD+BYyBIYBnGyXEKGrU1M0mfYuBkJlWXQmROSw7CcNwp04AAUXlIV4FAMBnGAdB6hnBoPVkLQGBIPhbAdLtNXQEhUAENJMAAD0QTBPSqLR8mPVJGAEOdnAdDi+AYeBNTgLjMGQfCPA7ZA+LE8UexlOV+0RQdVRHa8x0TZNp1TY101rc1nzga1X1XQs5AAdgABl-L8AJkICEnpIA

LMK if you want me to turn the TS playground code above into a CodeSandbox example; happy to do so.

To Reproduce

Steps to reproduce the behavior:

  1. Create a producer that accepts a TS type that has a well-known symbol property
  2. Try to read that property or call a function that accepts a parameter of T from Draft<T>. Note that mutation is not required-- this problem affects read-only access.

Observed behavior

TS errors as noted above.

Expected behavior

No TS errors.

Environment

We only accept bug reports against the latest Immer version.

  • Immer version:
  • I filed this report against the latest version of Immer
  • [n/a (TS only)] Occurs with setUseProxies(true)
  • [n/a (TS only)] Occurs with setUseProxies(false) (ES5 only)
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從這裡開始

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  3. Fork 儲存庫，在一個分支上完成修改。
  4. 送出 Pull Request，並在描述裡引用這個 Issue 編號。

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