Syntax errors in assembly included from another file produce confusing output

[ketsuban]

The following is a sufficiently supported pattern in Rust to get a mention in the unstable book.

#![feature(global_asm)]
global_asm!(include_str!("something_neato.s"));

However, if the included assembly contains a syntax error (such as the ARM instruction push {r2, r3, r12, lr} - the solution* is to double the curly brackets to prevent the compiler from interpreting them as a template string) the error you get is somewhat confusing since it blames a seemingly arbitrary point potentially in a completely different source file from the actual error.

error: invalid asm template string: expected `'}'`, found `','`
  --> src\bit_utils.rs:36:18
   |
36 |   let mask = (((1_u64 << (H - L + 1)) - 1) << L) as u16;
   |               -  ^ expected `}` in asm template string
   |               |
   |               because of this opening brace
   |
  ::: src\lib.rs:6:13
   |
6  | global_asm!(include_str!("rt0.S"));
   |             --------------------- in this macro invocation
   |
   = note: if you intended to print `{`, you can escape it using `{{`

The correct error here would presumably look something like this.

error: invalid asm template string: expected `'}'`, found `','`
  --> src\rt0.S:98:12
   |
98 |   push  {r2, r3, r12, lr}
   |         -  ^ expected `}` in asm template string
   |         |
   |         because of this opening brace
   |
  ::: src\lib.rs:6:13
   |
6  | global_asm!(include_str!("rt0.S"));
   |             --------------------- in this macro invocation
   |
   = note: if you intended to print `{`, you can escape it using `{{`

This may be related to #81751 - I'm not familiar enough with compiler internals to say, so I erred on the side of posting a new issue.

*or at least a solution - another would be to special-case this pattern as unable to use template strings