Consider the code below:
function f(x : number) {
if (x === 1) {
if (x === 2) {} // error
}
else {
if (x === 1) {} // OK
}
}
The compiler flags an error on x === 2.
This is because if the code reaches this block, x must be 1 since x === 1 passed.
And as 1 and 2 are distinct, it's impossible for x to be both.
Surprisingly, the compiler allows the second x === 1 within the else statement.
This seems illogical because x already failed the check for x === 1 in the initial if.
Since x cannot simultaneously satisfy x === 1 and !(x === 1), the second if should generate the same error as x === 2.
How can this happen? Is it an unimplemented feature of complex flow analysis? Is it a bug? Or could there be some hidden logic that ultimately makes sense in this scenario?
Thank you.