Description
🐛 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)
*/
});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:
- Create a producer that accepts a TS type that has a well-known symbol property
- Try to read that property or call a function that accepts a parameter of
TfromDraft<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)