Attributes used with derive have incorrect span information

[sgrif]

Given the following struct:

#[derive(AsChangeset)]
#[table_name = "users"]
struct UserForm {
    id: i32,
    name: String,
}

the input to the custom derive will have incorrect span information for every token in the table_name attribute except for the pound. Every other token will have the span Span { lo: BytePos(0), hi: BytePos(0), ctxt: #0 }.

[dtolnay]

I was able to reproduce this with the following macro on rustc 1.25.0-nightly (56733bc 2018-02-01). The four tokens in the attribute, [...], table_name, =, "users", all have span Span { lo: BytePos(0), hi: BytePos(0), ctxt: #0 }.

src/main.rs

#![feature(proc_macro)]

extern crate repro;
use repro::AsChangeset;

#[derive(AsChangeset)]
#[table_name = "users"]
struct UserForm {
    id: i32,
    name: String,
}

fn main() {}

src/lib.rs

#![feature(proc_macro)]

extern crate proc_macro;
use proc_macro::TokenStream;

#[proc_macro_derive(AsChangeset, attributes(table_name))]
pub fn derive(input: TokenStream) -> TokenStream {
    for tt in input {
        println!("{:#?}", tt);
    }
    TokenStream::empty()
}

[sgrif]

The span of the pound token is wrong as well. An error on that span shows the right source code, but has the wrong file/line numbers displayed.

error: `treat_none_as_null` must be in the form `treat_none_as_null = "true"`
 --> <macro expansion>:1:1
  |
1 | #[changeset_options(treat_none_as_null("true"))]
  | ^