I have the same sample program as over in #424:

use structopt::StructOpt;

macro_rules! Command {
  ( $name:ident, [
    #[$meta:meta] $var:ident($inner:ty)
  ] ) => {
    #[derive(Debug, PartialEq, structopt::StructOpt)]
    enum $name {
      #[$meta] $var($inner),
    }
  };
}

Command! {GitCmd, [
  #[structopt(external_subcommand)]
  Ext(Vec<String>)
]}

fn main() {
  assert_eq!(
    GitCmd::from_iter(&["test", "git", "status"]),
    GitCmd::Ext(vec!["git".to_string(), "status".to_string()]),
  );
}

Now it fails to compile with:

error[E0425]: cannot find value `other` in this scope
  --> src/main.rs:16:11
   |
16 |   Ext(Vec<String>)
   |           ^^^^^^ not found in this scope

Seems to be yet another span issue. Also related is 0852b91, which changes the error from something along the lines of

error: The type must be either `Vec<String>` or `Vec<OsString>` to be used with `external_subcommand`.
   --> main.rs:25:18
    |
25  |             $var$(($inner))?,
    |                    ^^^^^^
    |

to the above. I am using Rust 1.48. I am absolutely positive it worked with earlier Rust versions at some point (in fact, I still have the logs of a successful CI run with 1.42.0), but I can't try with all other Rust versions right now. I experimented with structopt 0.3.17 to 0.3.20, all exhibit either of the issues mentioned above (so the combination of structopt 0.3.17 with structopt-derive 0.4.10 and Rust 1.42.0 is/was known good)