Control flow analysis could affect the scope of a type guard

[chuckjaz]

Consider,

function isString(obj: any): obj is string {
    return typeof typeof obj === "string"; 
}

function foo(value: (string|number)): number {
    if (isString(value)) {
        return value.indexOf('foo')
    } else
        return value;
}

function bar(value: (string|number)): number {
    if (isString(value)) {
        return value.indexOf('foo')
    }
    return value;
}

Expected: Both foo and bar type-check correctly.
Received: bar reports that value is not assignable to number.

Flow analysis could be used here to determine value can only be number in all the code paths that arrive at the final return.

[mhegazy]

looks like a duplicate of #2388

[chuckjaz]

Search fail. Sorry about that.