I'm testing against 2.0.0-rc.1.

The derive macros cause syntax errors when given a struct with a default generic argument, such as:

#[derive(Encode)]
struct Foo<Bar=Baz> {}

This produces the following error:

error: Invalid rust syntax, expected ', > or an ident, got Some(Punct { ch: '=', spacing: Alone, span: #0 bytes(104880..104881) })
  --> src/xxx.rs:87:15
   |
87 | struct Foo<Bar=Baz> {}

(I tested this in some project, so there is an unhelpful line number.)