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** ```ts // 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…