error[E0308]: arguments to this function are incorrect
  --> tests/compile/derive-invalid-default-strategy.rs:7:20
   |
7  |   #[merge(strategy = my_custom_merge_strategy)]
   |  ____________________-^^^^^^^^^^^^^^^^^^^^^^^
8  | | struct S {
9  | |     field1: u16,
   | |          -
   | |          |
   | |__________expected `&mut u8`, found `&mut u16`
   |            expected `u8`, found `u16`
   |
   = note: expected mutable reference `&mut u8`
              found mutable reference `&mut u16`
note: function defined here
  --> tests/compile/derive-invalid-default-strategy.rs:12:4
   |
12 | fn my_custom_merge_strategy(left: &mut u8, right: u8) {
   |    ^^^^^^^^^^^^^^^^^^^^^^^^ -------------  ---------
help: you can convert a `u16` to a `u8` and panic if the converted value doesn't fit
   |
9  |     field1.try_into().unwrap(): u16,
   |           ++++++++++++++++++++