[Bug] Result of object rest isn't assignable to symbol index signature

[sounisi5011]

Bug Report

🔎 Search Terms

• PropertyDescriptorMap
• PropertyDescriptor
• Spread

🕗 Version & Regression Information

• This has changed since version 4.6

⏯ Playground Link

Playground link with relevant code:

• Nightly (fail)
• 4.7.0-beta (fail)
• 4.6.4 (fail)
• 4.5.5 (passed)

💻 Code

declare const properties1: { [x: string]: PropertyDescriptor };

// This will pass. This is because the type '{ [x: string]: PropertyDescriptor }' can be assigned to the type 'PropertyDescriptorMap'.
Object.defineProperties({}, properties1);

// But when it passes the spread syntax, it fails even though the types are the same.
const { ...properties2 } = properties1;
Object.defineProperties({}, properties2);

🙁 Actual behavior

I get the following error:

Argument of type '{ [x: string]: PropertyDescriptor; }' is not assignable to parameter of type 'PropertyDescriptorMap & ThisType<any>'.
  Type '{ [x: string]: PropertyDescriptor; }' is not assignable to type 'PropertyDescriptorMap'.
    Index signature for type 'symbol' is missing in type '{ [x: string]: PropertyDescriptor; }'.

But, type { [x: string]: PropertyDescriptor; } is assignable to type PropertyDescriptorMap. Objects copied with spread syntax cannot be assigned even though they have the same type.

🙂 Expected behavior

This type error does not occur. For the same type, it should be consistently assignable / non-assignable anywhere.

[MartinJohns]

I don't know if this is intentional, but a quick workaround is to write { [x: string | symbol]: PropertyDescriptor }.

[sounisi5011]

Yes. But in the actual code, we may use the spread syntax when we want to exclude some properties.

https://github.com/sounisi5011/npm-packages/blob/fdf42d3f512f5ed3cb24ee7c5056f96eeafbd014/packages/check-pid-file/src/index.ts#L15

The same error occurs in this case as well. Such code would require a type hack like the one below to set the proper type:

const oldErrorProperties = Object.getOwnPropertyDescriptors(oldError);
const { message: _1, stack: _2, ...newErrorProperties } =
    oldErrorProperties as (
        & typeof oldErrorProperties
        & { [x: symbol]: PropertyDescriptor }
    );
Object.defineProperties(newError, newErrorProperties);

Playground

[RyanCavanaugh]

Shorter repro:

const { ...properties2 } = {};
// Fails, should pass
const t1: { [x: symbol]: unknown } = properties2;
// OK
const t2: { [x: symbol]: unknown } = {};