cannot find macro compile_error in this scope

[smoelius]

A custom inner attribute (specifically, this one) applied at the crate root produces an error message like this:

error: cannot find macro `compile_error` in this scope
 --> src/main.rs:2:1
  |
2 | / #![feature(custom_inner_attributes, proc_macro_hygiene)]
3 | |
4 | | #![cast_checks::enable]
5 | |
6 | |
7 | | fn main() {
8 | | }
  | |_^
  |
  = help: consider importing one of these items:
          std::compile_error
          core::compile_error

I think the reason for the error message is that compile_error! is not qualified here:

syn/src/error.rs

Line 283 in e19a0fb

TokenTree::Ident(Ident::new("compile_error", start)),

In other words, I think it should be std::compile_error!.

To be clear, I don't think that making this error go away will make the crate-level, custom inner attribute work---I think there are other problems.

But making this error go away would help to expose those other problems and make them easier to diagnose.

Would you agree?

I could submit a PR, but I would need a pointer or two on how to change the referenced code. My attempts to add std:: thus far have been unsuccessful.