Repository: TypeScript
Issue: Optional type as required if used in one branch of nested promises
Labels: Needs Investigation,Rescheduled

# Bug Report

The system falsely reports an optional property as required if one branch returns the one optional property, but a second branch skips it and returns another optional property.

### 🔎 Search Terms

promise, catch, optional property

### 🕗 Version & Regression Information

* 3.1.4
* nightly (4.2.0-dev.20210112)

### ⏯ Playground Link

This playground shows 3 examples of the code posted below, where I commented out specific parts of the code. If you remove the comments in a variant, it will show the error:

https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmYcAiBDGG4F44AKUEAtgJYDOwAPAN4BQcTcUwAjgK5msAmREKWIgBccAHYcSAI2BQA3I2YCYZCGIwAbfoKQBGAPyiJ02QuZxlq9VuI7EAJkPjJM+fQC+APjNx6AYzUKeAA3DCgyDCkNYFFMbDxCYnIqADpWCggNYOAACnsASnoUmAALYDEcnLBiACtgPxh8vE84BiYyADM4HIBCaog6hqa25lYYDigxVsVzVk5uYD5bWSRRAAYAGhmlMBU1TW0VxF1Re03t9x93OGANKmnzAHpHsYmp-mTgNOAMrNyAbQAuvlimUKjkmrgWiNZsBxpMHuZRuwuLxDkJ1lskTs9tZ0Uh7KJdOdsZdts93Pkrh5Cik-Fg-CVKpCWjkRpZ9jYBEcTnBiViWCiFktuRi4OdKVT6P5AiEwhEosBCegsDh8B9KF90plsnlaaVypV+oNGs1EZ1un1avVTTDBfCpnamHNUYt8SJxQKno8OXjlkJeWcvXAyUxrrd7nbXgiNaltX8ckCQQbwSzEbCHemkS7he7MdtzL6Dv6CUSSUjQ8xKdTKUV6TBGcyzWzFEWuXZefzFDm0SWPRL8lKZWIgnBQuFItEAMyxVUJWNan463IFIopo3WoZmkYW3rGm3DbbRx0FwXzXui1ae09t92B8thq43O6oKNwt6JUia76-XVJ0GGhC26nseWawuebp9vm2JMLefbKl2pI+GGUphjS9DPHSDJMkBULdAwzywbsVjFpexxllshFnq6Ip2PmFKDgow6-F8GgQAA5jk44KtEGxjvKk5Knx3GCVOhRAA

### 💻 Code

```ts
export type Data = Promise<{
    requiredProperty: number;
    optionalProperty1?: number;
    optionalProperty2?: number;
}>;
  
const variable: Data = Promise.resolve(2)
.then((project) => {
  if (!project) {
    return {
      requiredProperty: 0,
      optionalProperty1: 20,
    };
  } else {
    return Promise.resolve([]).then(() => {
      return {
        requiredProperty: 0,
        optionalProperty2: 10,
      };
    });
  }
})
.catch(() => ({
  optionalProperty1: 10,
  requiredProperty: 0,
}));
```

### 🙁 Actual behavior

```
⠏ (3/3) Building...
test.ts:7:7 - error TS2322: Type 'Promise<number | { optionalProperty1: number; requiredProperty: number; }>' is not assignable to type 'Data'.
  Type 'number | { optionalProperty1: number; requiredProperty: number; }' is not assignable to type '{ requiredProperty: number; optionalProperty1?: number | undefined; optionalProperty2?: number | undefined; }'.
    Type 'number' is not assignable to type '{ requiredProperty: number; optionalProperty1?: number | undefined; optionalProperty2?: number | undefined; }'.

7 const variable: Data = Promise.resolve(2)
        ~~~~~~~~


test.ts:8:7 - error TS2345: Argument of type '(project: number) => Promise<{ requiredProperty: number; optionalProperty2: number; }> | { requiredProperty: number; optionalProperty1: number; }' is not assignable to parameter of type '(value: number) => { requiredProperty: number; optionalProperty2: number; } | PromiseLike<{ requiredProperty: number; optionalProperty2: number; }>'.
  Type 'Promise<{ requiredProperty: number; optionalProperty2: number; }> | { requiredProperty: number; optionalProperty1: number; }' is not assignable to type '{ requiredProperty: number; optionalProperty2: number; } | PromiseLike<{ requiredProperty: number; optionalProperty2: number; }>'.
    Type '{ requiredProperty: number; optionalProperty1: number; }' is not assignable to type '{ requiredProperty: number; optionalProperty2: number; } | PromiseLike<{ requiredProperty: number; optionalProperty2: number; }>'.
      Property 'optionalProperty2' is missing in type '{ requiredProperty: number; optionalProperty1: number; }' but required in type '{ requiredProperty: number; optionalProperty2: number; }'.

8 .then((project) => {
        ~~~~~~~~~~~~~~

  test.ts:18:9
    18         optionalProperty2: 10,
               ~~~~~~~~~~~~~~~~~~~~~
    'optionalProperty2' is declared here.

ℹ (3/3) Building...found 2 errors
```

### 🙂 Expected behavior

Should work without reporting any errors.

Please explain if this was intended in any way.