type MyInt = i32;

const MY_CONST: MyInt = 10;

cbindgen will produce a "Unhandled const definition" error on MY_CONST because MyInt is not a "can_handle" type
https://github.com/eqrion/cbindgen/blob/1fc4cb072422e722f8bcb3af5766f84587a180c6/src/bindgen/ir/constant.rs#L393-L395
https://github.com/eqrion/cbindgen/blob/1fc4cb072422e722f8bcb3af5766f84587a180c6/src/bindgen/ir/constant.rs#L366-L374

The "can_handle" restriction looks artificial and unnecessary, if it is commented out, then the correct constant definition is generated.

// C++
static const MyInt MY_CONST = 10;

// C
#define MY_CONST 10

In both cases it doesn't matter what MyInt actually is, cbindgen just can put it into the constant definition textually and it will work in most cases if the right hand side can be converted to C/C++.