error[E0283]: type annotations needed: cannot satisfy `T: FnMut<(&'a (),)>`
  --> $DIR/issue-85735.rs:7:8
   |
LL |     T: FnMut(&'a ()),
   |        ^^^^^^^^^^^^^
   |
note: multiple `impl`s or `where` clauses satisfying `T: FnMut<(&'a (),)>` found
  --> $DIR/issue-85735.rs:7:8
   |
LL |     T: FnMut(&'a ()),
   |        ^^^^^^^^^^^^^
LL |
LL |     T: FnMut(&'b ()),
   |        ^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0283`.