error: recursion limit reached while expanding the macro `prob1`
  --> $DIR/issue-16098.rs:7:18
   |
LL |             $n + prob1!($n - 1);
   |                  ^^^^^^^^^^^^^^
...
LL |     println!("Problem 1: {}", prob1!(1000));
   |                               ------------ in this macro invocation
   |
   = help: consider adding a `#![recursion_limit="128"]` attribute to your crate

error: aborting due to previous error