error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL | / macro_rules! pong {
LL | |     () => { syntax error };
   | |                    ^^^^^ expected one of 8 possible tokens
LL | | }
   | |_- in this expansion of `pong!`
...
LL |       pong!();
   |       ------- in this macro invocation

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL | /  macro_rules! pong {
LL | |      () => { syntax error };
   | |                     ^^^^^ expected one of 8 possible tokens
LL | |  }
   | |__- in this expansion of `pong!` (#2)
...
LL |        ping!();
   |        ------- in this macro invocation (#1)
   |
  ::: $DIR/auxiliary/ping.rs:5:1
   |
LL |  / macro_rules! ping {
LL |  |     () => {
LL |  |         pong!();
   |  |         ------- in this macro invocation (#2)
LL |  |     }
LL |  | }
   |  |_- in this expansion of `ping!` (#1)

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL | /  macro_rules! pong {
LL | |      () => { syntax error };
   | |                     ^^^^^ expected one of 8 possible tokens
LL | |  }
   | |__- in this expansion of `pong!` (#5)
...
LL |        deep!();
   |        ------- in this macro invocation (#1)
   |
  ::: $DIR/auxiliary/ping.rs:5:1
   |
LL |  / macro_rules! ping {
LL |  |     () => {
LL |  |         pong!();
   |  |         ------- in this macro invocation (#5)
LL |  |     }
LL |  | }
   |  |_- in this expansion of `ping!` (#4)
...
LL | /  macro_rules! deep {
LL | |      () => {
LL | |          foo!();
   | |          ------ in this macro invocation (#2)
LL | |      }
LL | |  }
   | |__- in this expansion of `deep!` (#1)
...
LL | /  macro_rules! foo {
LL | |      () => {
LL | |          bar!();
   | |          ------ in this macro invocation (#3)
LL | |      }
LL | |  }
   | |__- in this expansion of `foo!` (#2)
...
LL | /  macro_rules! bar {
LL | |      () => {
LL | |          ping!();
   | |          ------- in this macro invocation (#4)
LL | |      }
LL | |  }
   | |__- in this expansion of `bar!` (#3)

error: aborting due to 3 previous errors