Could you let the comment also explain when this happens? I'm not sure why we need to support this. Is it used only for Rust-level unit tests?

Sure. It's used in HIR dump, graphviz output, and iongraph output.

🤔

My question was on this "empty string if iseq is not available" line, and I meant to ask "Is empty string used only for Rust-level unit tests?". Are you sure you print an empty string here on HIR dump?

Oh I thought you meant the return value of this function in general.

Insn can also be printed in panic/debug messages too, like in disasm.rs we have:

    // For each instruction in this block
    for insn in insns.as_ref() {
        // ...
        writeln!(&mut out, "  {}", format!("{insn}").trim()).unwrap();
    }

In these cases, I think the fmt implementation for Display trait would be called, which can't access iseq:

impl std::fmt::Display for Insn {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.print(&PtrPrintMap::identity(), None).fmt(f)
    }
}

So the empty string is for those cases.

ok, that's probably useful to support then (as I asked above, please consider leaving the context in this line 🙏)

Added a comment 👍

nit: does not return empty anymore if iseq is not available--returns none. pls fix comment