Incorrect span columns for `<` open angle bracket symbol

[chinedufn]

This might be an issue for other tokens as well, I just ran into it for < open angle bracket.

The spans for the < token have incorrect columns. They appear to be one less than what the real value should be.

I've reproduced the issue in a minimal repository on GitHub.

git clone https://github.com/chinedufn/rustc-span-error
cd rustc-span-error
cargo test # You'll see a failing test with the incorrect span column

I'll paste the code below since it's short:

src/lib.rs

#![feature(proc_macro_hygiene)]

use proc_macro_example::example;

fn foo () {
    example! {
ABC<
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn foo () {
        
    }
}

proc macro

#![feature(proc_macro_span)]

extern crate proc_macro;

use proc_macro::TokenStream;
use quote::quote;

#[proc_macro]
pub fn example (input: TokenStream) -> TokenStream {
    let mut tokens = input.into_iter();

    // Assert ABC span start and end columns

    let abc = tokens.next().unwrap();
    assert_eq!(&abc.to_string(), "ABC");

    assert_eq!(abc.span().start().column, 0);
    assert_eq!(abc.span().end().column, 2);

    // Assert `<` span start and end columns.
    // This will fail
    let bracket = tokens.next().unwrap();
    assert_eq!(&bracket.to_string(), "<");

    assert_eq!(bracket.span().end().column, 3);

    let empty = quote! {
    };

    empty.into()
}

[dtolnay]

I think the compiler is correct here. In your standalone repo, the assertion that is failing is the following one (not the one you commented):

assert_eq!(abc.span().end().column, 2);

because the end of ABC is in column 3.

 A B C <
↑ ↑ ↑ ↑ ↑
0 1 2 3 4

ABC goes from 0 to 3, < goes from 3 to 4.

In dtolnay/proc-macro2#166 (comment):

 T  a  g     <  /
↑  ↑  ↑  ↑  ↑  ↑  ↑
33 34 35 36 37 38 39

Tag goes from 33 to 36, < goes from 37 to 38.

FYI @alexcrichton

[chinedufn]

Ahhh sorry I misunderstood how columns worked. Thanks so much!