generic arrow functions are incorrectly identified as JSX elements

[mutsys]

TypeScript Version: 2.3.2

Code

this statement causes an error

const foo = <P>(bar: P): void => {
    console.log(bar);
};

while the equivalent statement written with the function keyword does not:

function foo<P>(bar: P): void {
    console.log(bar);
}

it seems that as long as there is some other statement that precedes the generic declaration, the statement is recognized as valid. this next example is also recognized as valid:

const foo = (): <P>(bar: P) => void => {
    return function<P>(bar: P): void {
        console.log(bar);
    };
}

however, changing the inner function to an arrow function also results in the same error.

Expected behavior:
the expression is evaluated and recognized as valid

Actual behavior:
an error is produced:

[ts] cannot find name 'P'.
[ts] JSX element 'P' has no corresponding closing tag.

[mhegazy]

looks like a duplicate of #15713