This is because the symbol b has two owner scopes, which makes rolldown consider it conflicted. So the symbol b was wrongly appiled the renaming logic and became b$1.

For input

// entry.js
(() => {
	function a() {
		b();
	}
	{
		var b = () => {
		};
	}
	a();
})();

The correct output should be

// entry.js
(() => {
	function a() {
		b();
	}
	{
		var b = () => {
		};
	}
	a();
})();

instead of https://github.com/rolldown-rs/rolldown/blob/b3c5e0178aec3381b54ed9bde3ee94bfa0fc0cc2/crates/rolldown/tests/esbuild/default/nested_scope_bug/artifacts.snap.

Related issues:

• [bug][scope analysis] A symbol has two owner scopes in the same time oxc-project/oxc#2205