Don't latebind global JS property assignments

[sandersn]

Late binding assumes a parent symbol. Currently, the binder does not check whether an assignment declaration has a parent symbol exists before creating a symbol for late binding. The easiest place to encounter this is with window assignments, because global (script) files have no symbol, unlike module files:

const X = "X"
window[X] = () => 1

It is possible to special-case window for late binding similar to the way that it's done for normal binding, or even any top-level assignment declaration in a global file. But I don't think there's enough value. For now, this PR prevents binding entirely for a dynamic name when there is no parent symbol.

Fixes #61583

[Copilot]

Pull Request Overview

This PR fixes an issue with latebound global JavaScript property assignments by preventing binding for dynamic names when no parent symbol is present.

• Added an early return in the binder when parentSymbol is undefined in dynamic name assignments
• Updated the test case to verify that global assignments to window properties using dynamic names are not latebound

Reviewed Changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/cases/conformance/salsa/lateboundWindowToplevelAssignment.ts	Added a test to verify that global dynamic assignments (e.g. window[...] = …) do not create a symbol
src/compiler/binder.ts	Added a check for a missing parent symbol before binding dynamic names to prevent late binding in global files

Files not reviewed (2)

• tests/baselines/reference/lateboundWindowToplevelAssignment.symbols: Language not supported
• tests/baselines/reference/lateboundWindowToplevelAssignment.types: Language not supported

[Copilot]

The added check prevents binding for dynamic property assignments when no parent symbol is present, avoiding unintended symbol creation in global files. Consider adding an inline comment here to clarify why binding is skipped in this scenario for future maintainability.

Suggested change

	else if (hasDynamicName(node)) {
	if (!parentSymbol) {
	return;
	}
	else if (hasDynamicName(node)) {
	// Skip binding for dynamic property assignments when no parent symbol is present.
	// This prevents unintended symbol creation in global files, ensuring correctness.
	if (!parentSymbol) {
	return;
	}

[sandersn]

I don't really agree, but I would change my mind if a human spoke up saying that they do.

[sandersn]

Having type error shows that binding didn't happen.