false positive for no-string-based-set-interval rule only when type checking is enabled

[ChrisMBarr]

typescript version 2.2.2
ts-lint version 5.2.0
running via gulp-tslint 8.0.0

---

When type checlking is enabled the following code fails with ERROR: 84:32 no-string-based-set-interval Forbidden setInterval string parameter: process.

const process = () => {
    for (let i = 0; i < queue.length; i++) {
        const qi = queue.splice(0, 1)[0];
        if (qi) {
            sendRequest(qi);
        } else {
            break;
        }
    }
};

const intervalLoop = window.setInterval(process, 100);  // <-- failure reported here

This only fails when rule type checking is enabled though, even though this rule says it does not require type checking! No failures here are produced when type checking is not enabled.

However, writing it like this does not produce a failure:

const intervalLoop = window.setInterval(() => {
    for (let i = 0; i < queue.length; i++) {
        const qi = queue.splice(0, 1)[0];
        if (qi) {
            sendRequest(qi);
        } else {
            break;
        }
    }
}, 100);

I'm not sure why... I ended up keeping the re-written version since it's simpler, but this feels like a bug.

[JoshuaKGoldberg]

The rule doesn't require type checking, but it will take advantage of a TypeScript program if provided one. This must be a bug specifically in that optional logic.

Scanning through the code, noStringBasedSetIntervalRule.ts uses a NoStringParameterToFunctionCallWalker, which uses its isExpressionEvaluatingToFunction. I'd check there for logic that requires this.typeChecker.

[JoshuaKGoldberg]

💀 It's time! 💀

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