Optional type as required if used in one branch of nested promises

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

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.