error: lifetime parameter `'a` only used once
  --> $DIR/issue-104440.rs:63:8
   |
LL |     m!('a);
   |        ^^
   |        |
   |        this lifetime...
   |        ...is used only here
   |
note: the lint level is defined here
  --> $DIR/issue-104440.rs:2:9
   |
LL | #![deny(single_use_lifetimes)]
   |         ^^^^^^^^^^^^^^^^^^^^

error: lifetime parameter `'a` only used once
  --> $DIR/issue-104440.rs:38:30
   |
LL |         fn f<'b, 'c, $a: 'b, 'a: 'c>(t1: &$a(), t2: &'a ()) -> (&'b (), &'c ()) {
   |                              ^^ this lifetime...     -- ...is used only here
...
LL |     m!('a);
   |     ------ in this macro invocation
   |
   = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 2 previous errors