file-level doctests have wrong file/line mapping when module has use-level doctest

[Swatinem]

I have a module in an external file.
When I add doctests to both the pub mod X; item, and the X.rs file, the file-level doctest has the wrong filename/line information.

Consider the following example:

--- lib.rs ---
//! crate-level doctest
//!
//! ```
//! // lib.rs line 3
//! assert_eq!(1, 1);
//! ```

pub mod mod_with_file_doctest;

/// mod reference-level doctest
///
/// ```
/// // lib.rs line 12
/// assert_eq!(1, 1);
/// ```
pub mod mod_with_ref_doctest;

/// mod reference-level doctest
///
/// ```
/// // lib.rs line 20
/// assert_eq!(1, 1);
/// ```
pub mod mod_with_both_doctests;

--- mod_with_file_doctest.rs ---

//! mod file-level doctest
//!
//! ```
//! // mod_with_file_doctest.rs line 3
//! assert_eq!(1, 1);
//! ```

--- mod_with_both_doctests.rs ---

//! mod file-level doctest
//!
//! ```
//! // mod_with_both_doctests.rs line 3
//! assert_eq!(1, 1);
//! ```

Running cargo test, I get the following output:

running 5 tests
test src\lib.rs - mod_with_both_doctests (line 20) ... ok
test src\lib.rs - mod_with_both_doctests (line 26) ... ok
test src\lib.rs - (line 3) ... ok
test src\mod_with_file_doctest.rs - mod_with_file_doctest (line 3) ... ok
test src\lib.rs - mod_with_ref_doctest (line 12) ... ok

The line test src\lib.rs - mod_with_both_doctests (line 26) should actually be test src\mod_with_file_doctest.rs - mod_with_file_doctest (line 3)

Looks like that the line 26 is somehow relative to the pub mod line.

I will look into this and try to get a PR together that fixes this.