#[derive(StructPath)]Expand description
#[derive(StructPath)] records a struct’s declared field names as
#[doc(hidden)] associated consts, so paths!(Type::*) can return them
without the caller listing every field by hand. Supports only a struct
with named fields and, at most, lifetime generic parameters; anything
else is a compile_error! on the offending item, spanned at the
specific token that disqualifies it.