Line numbers in diagnostics for doctests are off by number of preceding hidden lines that aren't use core;

[zopsicle]

Code

/// ```
/// # use playground::f;
/// x
/// ```
pub fn f()
{
    todo!()
}

Note that the expression x occurs on line 3 in the source code.

Current output

error[E0425]: cannot find value `x` in this scope
 --> src/lib.rs:4:1
  |
6 | x
  | ^ help: a function with a similar name exists: `f`
  |
 ::: /playground/src/lib.rs:5:1
  |
5 | pub fn f()
  | ---------- similarly named function `f` defined here

Note that the diagnostic refers to line 4.

Desired output

error[E0425]: cannot find value `x` in this scope
 --> src/lib.rs:3:1
  |
6 | x
  | ^ help: a function with a similar name exists: `f`
  |
 ::: /playground/src/lib.rs:5:1
  |
5 | pub fn f()
  | ---------- similarly named function `f` defined here

Rationale and extra context

No response

Other cases

No response

Rust Version

$ rustc --version --verbose
rustc 1.77.0 (aedd173a2 2024-03-17)
binary: rustc
commit-hash: aedd173a2c086e558c2b66d3743b344f977621a7
commit-date: 2024-03-17
host: x86_64-unknown-linux-gnu
release: 1.77.0
LLVM version: 17.0.6

Anything else?

This doesn't always seem to happen, for example in the following example it does not:

/// ```
/// # use core;
/// x
/// ```
pub fn f()
{
}

error[E0425]: cannot find value `x` in this scope
 --> src/lib.rs:3:1
  |
4 | x
  | ^ not found in this scope

I'm not sure what makes the difference. The only difference in the code is that one imports playground::f and the other imports core.

[GuillaumeGomez]

The problem is actually a bit more complicated than just an offset. For example:

// blabla

///
///
/// ```
/// # use playground::f;
/// x
/// ```
pub fn f()
{
    todo!()
}

It will give:

$ rustdoc --test foo2.rs 

running 1 test
test foo2.rs - f (line 5) ... FAILED

failures:

---- foo2.rs - f (line 5) stdout ----
error[E0432]: unresolved import `playground`
 --> foo2.rs:6:5
  |
3 | use playground::f;
  |     ^^^^^^^^^^ maybe a missing crate `playground`?
  |
  = help: consider adding `extern crate playground` to use the `playground` crate

error[E0425]: cannot find value `x` in this scope
 --> foo2.rs:7:1
  |
4 | x
  | ^ not found in this scope

error: aborting due to 2 previous errors

As you can see, even though I added a lot of lines before, the lines didn't change for the error messages. It's because we generate tests outside of this code and rustc only has information about this. I plan to rework doctests in the near future to improve such issues.