Adding generic parameter to a lambda function removes typing from the function argument

TypeScript Version: 3.2.2

Search Terms: generic removes parameter type

Code

// OKAY
// declare const labmda function with typings, then implement with minimal type annotations.
// "input" has type of "string".
export const foo: (input: string) => string
    = (input) => (input);

// OKAY
// declare const lambda generic function without typings, then implement with full inline type annotations.
// "input" has type of "string".
export const bar
    = <TResult>(input: string) => ({ } as Partial<TResult>);

// ERROR
// declare const labmda generic function with typings, then implement with minimal type annotations.
// "input" has type of "any".
export const baz: <TResult>(input: string) => Partial<TResult>
    = <TResult>(input) => ({ [input]: input } as Partial<TResult>);

Expected behavior:
input is typed as string.

Actual behavior:
input is typed as any.

Playground Link: https://www.typescriptlang.org/play/index.html#src=%2F%2F%20OKAY%0D%0A%2F%2F%20declare%20const%20labmda%20function%20with%20typings%2C%20then%20implement%20with%20minimal%20type%20annotations.%0D%0A%2F%2F%20%22input%22%20has%20type%20of%20%22string%22.%0D%0Aexport%20const%20foo%3A%20(input%3A%20string)%20%3D%3E%20string%0D%0A%20%20%20%20%3D%20(input)%20%3D%3E%20(input)%3B%0D%0A%0D%0A%2F%2F%20OKAY%0D%0A%2F%2F%20declare%20const%20lambda%20generic%20function%20without%20typings%2C%20then%20implement%20with%20full%20inline%20type%20annotations.%0D%0A%2F%2F%20%22input%22%20has%20type%20of%20%22string%22.%0D%0Aexport%20const%20bar%0D%0A%20%20%20%20%3D%20%3CTResult%3E(input%3A%20string)%20%3D%3E%20(%7B%20%7D%20as%20Partial%3CTResult%3E)%3B%0D%0A%0D%0A%2F%2F%20ERROR%0D%0A%2F%2F%20declare%20const%20labmda%20generic%20function%20with%20typings%2C%20then%20implement%20with%20minimal%20type%20annotations.%0D%0A%2F%2F%20%22input%22%20has%20type%20of%20%22any%22.%0D%0Aexport%20const%20baz%3A%20%3CTResult%3E(input%3A%20string)%20%3D%3E%20Partial%3CTResult%3E%0D%0A%20%20%20%20%3D%20%3CTResult%3E(input)%20%3D%3E%20(%7B%20%5Binput%5D%3A%20input%20%7D%20as%20Partial%3CTResult%3E)%3B

(NOTE: options -> noImplicitAny to have the issue highlighted as an error.)

Related Issues:

https://github.com/Microsoft/TypeScript/issues/18606
I think this issue might be related, but I don't understand it enough to judge.
If this is the same issue then the answer is "this is correct, and a limitation of the type system", which is fair enough.

Beginne damit, das Beispiel im verlinkten TypeScript Playground mit aktiviertem noImplicitAny zu reproduzieren, und vergleiche anschließend die drei Lambda-Deklarationen sowie das zugehörige Issue #18606. Verfolge, wie die kontextbezogene Typisierung auf die Zuweisung der generischen Lambda angewendet wird. Als abgeschlossen gilt die Aufgabe, wenn festgestellt wurde, ob das Argument als string inferiert werden sollte, und bei bestätigtem Bug ein Regressionstest hinzugefügt wurde.