but we're not actually responsible for serializing it but rowan is.

That is wrong, rowan is not a rust-specific library and that behavior is tied to rust. So if \0 has to be turned into \u{0} for correctness purposes we have to do that here as well. Though I am not sure if this escape_default-ing is actually observable by rust code

Ah ok, thanks for the correction!

As for the correctness, there are several characters that we need to escape, see rust-lang/rust#50391 (comment), but we're already escaping them when we convert strings to TokenTrees here with str::escape_debug(), so we should already be correct. I've pushed a commit that replaces escape_debug() with escape_default() and that should output string literals expanded from macro in the same manner as rustc. How does this look now?

Thanks!
@bors r+

📌 Commit 4d5873e has been approved by Veykril

It is now in the queue for this repository.

⌛ Testing commit 4d5873e with merge b569bbb...

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing b569bbb to master...