Static `this` is undefined during recursive call

While using this in a static class method to recursively call itself works in the browser, it does not work with compiled code:

static buildTagCache(node, idCache) {
	if (!node || (node.nodeType !== 1)) return; // not an element node
	var nn = node.nodeName;
	if (nn === 'point' || nn === 'link') {
		// do some stuff
	}
	// search down
	util.do4children(node, n => {
		this.buildTagCache(n, idCache);
	});
}

has an undefined this at the child call.

_Originally posted by @ray007 in https://github.com/google/closure-compiler/issues/3553#issuecomment-590834733_

[ray007]

If it fixes the bug I’d probably use the flag. But it feels funny to require a flag to avoid a class of bugs…

[nreid260]

Thanks for point this out! This is a compiler option that would solve this, as @brad4d mentioned in the other thread, but it hasn’t be exposed as a flag yet. There’s a field in CompilerOptions called assumeStaticInheritanceRequired that just needs to be set true.

This option hasn’t been exposed mostly because it can really hurt RemoveUnusedCode, and also to try to reduce the number of compiler flags. However, issues like this may prioritize creating the flag.

Would you use such a flag?