Incomplete infer for generic types

TypeScript Version: 4.0.5

Search Terms:
typescript, infer, incomplete, unknown, generic

Expected behavior:
The compiler should be able to extract information of the generic Item type from the function definition and infer string.

Actual behavior:
The compiler is able to infer the Names type as { id: string } but the Item type is unknown.

Related Issues:

Code

interface LoaderConfig<Key, Item> {
  loadItems: (keys: readonly Key[]) => Promise<readonly Item[]>;
  getKey: (item: Item) => Key;
  makeCacheKey: (key: Key) => string;
}

type LoaderConfigByName<Names, Item> = {
  [name in keyof Names]: LoaderConfig<Names[name], Item>;
};

function makeLoader<Names, Item>(
  configs: LoaderConfigByName<Names, Item>
): void {
  console.log(configs);
}

makeLoader({
  id: {
    loadItems: async (keys: readonly string[]): Promise<readonly string[]> => {
      return await Promise.resolve(keys);
    },
    getKey: (item: string): string => item,
    makeCacheKey: (key: string): string => {
      return key;
    }
  }
});

"use strict";
function makeLoader(configs) {
    console.log(configs);
}
makeLoader({
    id: {
        loadItems: async (keys) => {
            return await Promise.resolve(keys);
        },
        getKey: (item) => item,
        makeCacheKey: (key) => {
            return key;
        }
    }
});

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "alwaysStrict": true,
    "esModuleInterop": true,
    "declaration": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "moduleResolution": 2,
    "target": "ES2017",
    "jsx": "React",
    "module": "ESNext"
  }
}

Playground Link: Provided

Commencez par le lien Playground fourni et l’exemple générique makeLoader utilisant TypeScript 4.0.5. Reproduisez le résultat de l’inférence et suivez le traitement du type générique Item par le compilateur. La tâche est terminée lorsque l’exemple infère Item comme étant string tout en préservant le type Names inféré.