Compilation failure with Generic, Promis and ReturnType

[ilchenkoArtem]

TypeScript Version: 3.7.x-dev.201xxxxx

Search Terms:
Promise, ReturnType, Generic
Code

interface IBusinessUnitModel {
  parentId?: number,
  environmentId?: number
}

interface IEnvironmentModel {
  guid?: string,
  readonly inheritance?: string,
  userDomainId?: number,
  friendlyName?: string
}

interface IDictionaries {
  environment: IEnvironmentModel[];
  businessUnit: IBusinessUnitModel[];
}

type DictionaryMethodsType = {
  [key in keyof IDictionaries]: () => Promise<IDictionaries[key]>
};

async function loadDictionary<T>(url:string): Promise<T[]> {
  const response = await fetch(`/api/${url}`);
  return await response.json()
}

const loadDictionaryMethods:DictionaryMethodsType = {
  environment: () => loadDictionary<IEnvironmentModel>('environments'),
  businessUnit: () => loadDictionary<IBusinessUnitModel>('businessUnit'),
}

export const loadDictionaryByName =
  <N extends keyof DictionaryMethodsType>(name: N):Promise<ReturnType<DictionaryMethodsType[N]>> => loadDictionaryMethods[name]()

Expected behavior:
Compilation successful

Actual behavior:
Compilation failure with error:

Type 'Promise<IEnvironmentModel[]> | Promise<IBusinessUnitModel[]>' is not assignable to type 'Promise<ReturnType<DictionaryMethodsType[N]>>'. Type 'Promise<IEnvironmentModel[]>' is not assignable to type 'Promise<ReturnType<DictionaryMethodsType[N]>>'. Type 'IEnvironmentModel[]' is not assignable to type 'ReturnType<DictionaryMethodsType[N]>'.

Playground Link:
https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgJICECuBnUFvYCqIwYAsgPYAmEANsgN4BQyyADnFBOKlQPwAuZCEwBbAEbQANC2TcAbsCgUQo7mF6DhYyVCYBfJk1CRYiFKgCiIRctXrKNes1YBzTMH5DsYKKFcyrFxwVCq0AJ7IoAAW0KRwIEhaPn4gAbI40AAiFKJwoJpCIhLSsjB+3FQRAHJwasm+-gZGJtDwSGhZwAhgwCqcwPiMsgpKKmrgQlY2Y-bgjnQA2gC6ANyy4jh4BMSkU1i4IPhEJOTUS2vNTGDhbChdPX0gnOFkEGDR1NgAKrcoALzDViLADWEEioGQYPCFBgnW6vX6FWwyyEAAoAJTIf4APmQAAVlKJgNgIAAeVAPRHPZGg8HLHEGdZMODYcKJZAwTCJanIWgUEJUp4vMnfHFozBQWgCFL+DFCQm5Enk74rPEuZAIFQ+ZBcbBsbUA5BwADu+TAnPeCGiaIABgB6OBsYD2gAkDEltH0tox6yC70lIGNZtIuvwBpApIAdAArbAqTFXLWRi38wUI4VQV7vT5UbACIVI7MfL6-O7YoFyGZ2CZgdFY3F8gVUQs08IU6y2cYOc60cUAclGNfU2H7GMCyE2h2OuzryEx2LxaZbGaLFIO2xOpAWfbR-anm9nY5khiYyZ1y9bL3Q4VqamxsjJ1TkAA9ICA81DwbDkFes28SzzMsIHFZ41CEap5UVYlSTJAAlAMoBAYCyT-Ytcx+P5FmqBk8UbS9VzbACMMWMCIGWRMgA

Related Issues:

[MartinJohns]

Simplified example code:

type Methods = { a: () => 'a', b: () => 'b' }
declare const methods: Methods;
const load = <K extends keyof Methods>(key: K): ReturnType<Methods[K]> => methods[key]();

Looks like a duplicate of #31811 to me.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.