Mismatched types do not have line number

[patientplatypus]

error[E0308]: mismatched types
  |
  = note: expected type `()`
             found type `std::vec::Vec<u8>`

^ That is incredibly frustrating.

EDIT:

Turns out that for macros this is an issue apparently (I asked on freenode).

#[wasm_bindgen]
pub extern fn handle_mouse_down_stroke(stroke_type: String, stroke_size: u32, stroke_rgba: Vec<u8>, canvas_width: u32, canvas_height: u32, x: u32, y: u32)
-> Vec<u8>

vs

#[wasm_bindgen]
pub extern fn handle_mouse_down_stroke(stroke_type: String, stroke_size: u32, stroke_rgba: Vec<u8>, canvas_width: u32, canvas_height: u32, x: u32, y: u32)
// -> Vec<u8>

This gives an error. This narrows down the field of bad error messages, but it is still an open issue.

[Mark-Simulacrum]

I suspect this is fixed now on nightly -- the extern fn syntax previously caused macro expansion to lose spans, but should no longer do so I believe (I don't have time to hunt down the PR).

Can you check on nightly?

[Mark-Simulacrum]

Ah, I did not remember correctly. This is tracked in #64561.