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 {
   |   ----------------- in this expansion of `ping!` (#1)
LL |       () => {
LL |           pong!();
   |           ------- in this macro invocation (#2)

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 {
   |   ----------------- in this expansion of `ping!` (#4)
LL |       () => {
LL |           pong!();
   |           ------- in this macro invocation (#5)
...
LL |   macro_rules! deep {
   |   ----------------- in this expansion of `deep!` (#1)
LL |       () => {
LL |           foo!();
   |           ------ in this macro invocation (#2)
...
LL |   macro_rules! foo {
   |   ---------------- in this expansion of `foo!` (#2)
LL |       () => {
LL |           bar!();
   |           ------ in this macro invocation (#3)
...
LL |   macro_rules! bar {
   |   ---------------- in this expansion of `bar!` (#3)
LL |       () => {
LL |           ping!();
   |           ------- in this macro invocation (#4)

error: aborting due to 3 previous errors