`format!` error messages point to wrong characters when using macro-generated literals

[Nemo157]

I tried this code:

fn main() {
    format!(concat!("{", "  f"));
}

I expected to see this happen:

error: invalid format string: expected `'}'`, found `'f'`
 --> src/main.rs:2:17
  |
2 |     format!(concat!("{", "  f"));
  |                      -      ^ expected `}` in format string
  |                      |
  |                      because of this opening brace
  |
  = note: if you intended to print `{`, you can escape it using `{{`

Instead, this happened:

error: invalid format string: expected `'}'`, found `'f'`
 --> src/main.rs:2:17
  |
2 |     format!(concat!("{", "  f"));
  |              -  ^ expected `}` in format string
  |              |
  |              because of this opening brace
  |
  = note: if you intended to print `{`, you can escape it using `{{`

Another more complicated example, is using include_str! (with a self-include to make playground testing easier):

fn main() {
    format!(include_str!("main.rs"));
}

Similar to #81070 it'd be very nice if this was able to point to the location in the included file, but if it can't it should probably have a simpler error message like "in external string included here".

Meta

Tested on stable 1.51.0 and 1.53.0-nightly (2021-04-27 727d101561f9b1e81c62)

[Nemo157]

Current output:

error: invalid format string: expected `'}'`, found `'f'`
 --> src/main.rs:2:13
  |
2 |     format!(concat!("{", "  f"));
  |             ^^^^^^^^^^^^^^^^^^^ expected `}` in format string
  |
  = note: if you intended to print `{`, you can escape it using `{{`
  = note: this error originates in the macro `concat` (in Nightly builds, run with -Z macro-backtrace for more info)

2 |     format!(include_str!("main.rs"));
  |             ^^^^^^^^^^^^^^^^^^^^^^^ expected `}` in format string

Not perfect as it could be possible to track the spans back to the actual source instead of just highlighting the whole macro, but seems good enough to consider this bug fixed.