Unhelpful error message in macros which invoke other macros

[tiffany352]

The problematic code:

macro_rules! x {
    ($a:expr, $b:expr) => {}
}

macro_rules! y {
    ($a:expr, $b:expr) => {
        x!($a, $b)
    }
}

// much later

fn foo() {
    macro_rules! x {
        ($a:expr) => {}
    }

    // later still

    y!(1, 2)
}

Rustc output:

error: no rules expected the token `,`
 --> <anon>:8:14
8 |>         x!($a, $b)
  |>              ^

Playpen link

This error points out that the y! macro performed an incorrect invocation of the x! macro, but fails to point out which x! macro in particular it is trying to invoke, or the location where the y! macro was invoked. In addition, it doesn't point out tokens which the macro would accept (in this case, the end of the invocation).

[eddyb]

cc @jonathandturner

[estebank]

Current output still doesn't point at the called macro's definition (like we do for functions):

error: no rules expected the token `,`
  --> src/main.rs:8:14
   |
8  |         x!($a, $b)
   |              ^
...
21 |     y!(1, 2)
   |     -------- in this macro invocation