BigInt should not be a subtype of an object type

[Vbitz]

TypeScript Version: 3.8.0-dev.20200111

Search Terms: "BigInt"

Code

declare function test<A, B extends A>(): void;

test<{t?: string}, object>();
test<{t?: string}, bigint>();
test<{t?: string}, number>();

Expected behavior: bigint should behave like number.

Actual behavior: BigInt instead behaves like a object.

Playground Link: https://www.typescriptlang.org/play/?target=99&ts=3.8.0-dev.20200111#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXwxAGcMAeAQQBp4AheEAD0NWCPnID4AKASgC54ANxxZgAbgBQEwiVIBvDAH4BJGFlQBzAL7UcAIwBW4DNx6SZZBcvir126nqwb1J3ueKWlKjGs074qMgAtnogMKZiQA

Related Issues:

Main BigInt Issue: #33871

[AnyhowStep]

Weird. I would have expected object to also fail.
Because B["t"] could be numberinside the function body.

(I'm on mobile, so the below might not compile, I'll fix it when I get on a computer)

function foo<A, B extends A>(a : A, b : B, k : keyof A): A {
  a[k] = b[k];
  return a;
}
foo<{t?:string}, object>(
  {},
  {t : 999},
  "t"
).t; //Expected: undefined|string, Actual: 999

---

But I guess the problem is that object is {} & not primitive, and {} should extend {t?:string}, according to TS.

And we don't have negative field types...

[sandersn]

Notably, number fails the common-property check. It doesn't give the expected "Type 'number' does not satisfy the constraint '{ t?: number }'." either.

This has been a bug since bigint was introduced as far as I can tell. Moving to 3.9.

[sandersn]

Now that I'm trying to fix this for 3.9, I can't repro either example. bigint and number behave the same in all versions of Typescript that I tested locally -- 3.2 through 3.8. @AnyhowStep's foo example correctly returns string | undefined. And the playground link in the OP only fails because bigint isn't found at all in that dev playground.

I'm going to close this for now, although it's possible that I'm missing something.

[Vbitz]

I can confirm the original Playground link I posted now doesn't find the BigInt declaration.

Here is a new playground link switched to the nightly version reproducing the same case with the same code.

TypeScript Version: Nightly

Code

declare function test<A, B extends A>(): void;

test<{t?: string}, object>();
test<{t?: string}, bigint>();
test<{t?: string}, number>();

Output

"use strict";
test();
test();
test();

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided