Type annotations cause contextual this in object literal returned from an async function to be inferred as Promise<This> | This #64954

🔎 Search Terms

"this" "Promise" "async" "function" "inferred" "inference" "type" "annotations" "return" "object" "literal" "method"

🕗 Version & Regression Information

This bug exists down to typescript 3.3.3333, which is the earliest version available in the playground.
(I think the playground wrongly displays 3.3.3 version as 3.3.3333)

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.3#code/MYewdgzgLgBFCm0CMMC8MCGECeZgwAoBKNAPhgG8AoGGAJ3igFc6xKbaYA3DAGyfgAuGAFYANB1oBbRgAsQAE2LtOnKLICWEGBAxQtAMw2JK3PgOFgmUgEbw6YmDPWLiwriA0KYAXwDcMJK+ErT+VD5UVKCQsAjQAEzCyqjkAAp0IFJa8AA81Ko8-EIwVrb2fkHO8kpE7p4KFT7k6Fi4+Mnk+fSMLGxdtIUWoiGcVa4k-ZwA9FMwAAJQEAC08AAeAA7wwFArdBl0wgAq2JswAOQUZkWW1nZ0AWM1dV4BPjAAPjDpmdkAMhoAa1yl0GxVKdwecnGzwavlIZxgChAJjAIFgun0EAM2DgsngMDWm228G8UBO+IuVyG4PKTihT249VeZwAdEFaOotDo9IZjNoQeYwbd7I5Hm5GV5fAEgj4RmEIkA

💻 Code

const test1 = async () => {
  return {
    value: 5,
    method() {
      this satisfies { value: number, method(): void }; 
    },
  };
}

const test2: () => Promise<{
    value: number;
    method(): void;
}> = async () => {
  return {
    value: 5,
    method() {
      // @ts-expect-error: Type '{ value: number; method(): void; } | PromiseLike<{ value: number; method(): void; }>' does not satisfy the expected type '{ value: number; method(): void; }'.
      this satisfies { value: number, method(): void }; 
    },
  };
}

🙁 Actual behavior

Actual this type: { value: number; method(): void; } | PromiseLike<{ value: number; method(): void; }>

🙂 Expected behavior

Expected this type: { value: number; method(): void }

Additional information about the issue

This probably a duplicate as it is a very old bug, but I couldn't find an existing issue.

Typescript lsp shows that type of a test1 is:

const test1: () => Promise<{
    value: number;
    method(): void;
}>

So types of test1 and test2 are exactly the same, but the contextual type information causes the incorrect type to be inferred.

in the real code this happens more often in async callbacks.

satisfies in the example is to just throw an error, so that ts-expect-error can be used.