Better macro errors for get_struct_fields

[ecoskey]

Objective

• Currently, the error span for get_struct_field when encountering an enum or union points to the macro invocation, rather than the enum or union token. It also doesn't mention which macro reported the error.

Solution

• Report the correct error span
• Add parameter for passing in the name of the macro invocation

Testing

Bevy compiles fine with this change

Migration Guide

// before
let fields = get_struct_fields(&ast.data);

// after
let fields = get_struct_fields(&ast.data, "derive(Bundle)");