bincode_derive does not like generic parameters with defaults

[udoprog]

I'm trying to add bincode to musli benchmarks, and I want to derive Decode on something like the following:

use bincode::Decode;

#[derive(Decode)]
pub struct Mesh<V: AsRef<[Triangle]> = Vec<Triangle>> {
    pub triangles: V,
}

#[derive(Decode)]
struct Triangle {
    x: u32,
    y: u32,
    z: u32,
}

I see this:

Compile errors

error: generic parameters with a default must be trailing
 --> tests/examples/bincode-derive.rs:4:17
  |
4 | pub struct Mesh<V: AsRef<[Triangle]> = Vec<Triangle>> {
  |                 ^

error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
 --> tests/examples/bincode-derive.rs:4:17
  |
4 | pub struct Mesh<V: AsRef<[Triangle]> = Vec<Triangle>> {
  |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #36887 <https://github.com/rust-lang/rust/issues/36887>
  = note: `#[deny(invalid_type_param_default)]` on by default

error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
 --> tests/examples/bincode-derive.rs:4:17
  |
4 | pub struct Mesh<V: AsRef<[Triangle]> = Vec<Triangle>> {
  |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #36887 <https://github.com/rust-lang/rust/issues/36887>

error: could not compile `tests` (example "bincode-derive") due to 5 previous errors

In my mind, it should be possible to derive this, all though ultimately the Decode implementation would have to be conditional on implementing Decode, either implicitly or explicitly with bounds parameters.

Reference: udoprog/musli#266

[VictorKoenders]

Definitely a bug, thanks for reporting!

[VictorKoenders]

Related (but not duplicate) to #769