possible bug in procedural macro implementation?

[db48x]

I wrote a procedural macro which emits code containing a reference to std::foo::bar, and got this error:

error[E0433]: failed to resolve. Could not find `std` in `{{root}}`
 --> src/lib.rs:4:1
  |
4 | #[lisp_fn]
  | ^^^^^^^^^^ Could not find `std` in `{{root}}`

I've made a simplified testcase and put it online at https://github.com/db48x/legendary-octo-bassoon; if you check it out and run cargo test, you'll see the same error message. Obviously the testcase itself could be at fault, but it doesn't seem likely.

[pietroalbini]

Duplicate of #47314.