Doc-test reports “expected item, found keyword let” when the actual problem is a missing semicolon elsewhere

To reproduce

/// # Example
///
/// ```
/// use test_lib::add;
///
/// let p = add(3, 2);
///
/// assert_eq!(p, 5);
/// // missing a semicolon next line
/// assert_eq!(add(2, 2), 4)
/// assert_eq!(add(5, 0), 5);
/// ```
pub fn add(left: u64, right: u64) -> u64 {
    left + right
}

1. Put the above code in src/lib.rs of a new cargo project named test_lib.

2. Run:

   cargo test --doc
   

Actual output

   Doc-tests test_lib

running 1 test
test src\lib.rs - add (line 3) ... FAILED

failures:

---- src\lib.rs - add (line 3) stdout ----
error: expected item, found keyword `let`
 --> src\lib.rs:6:1
  |
3 | let p = add(3, 2);
  | ^^^
  | `let` cannot be used for global variables
  | help: consider using `static` or `const` instead of `let`
  |
  = note: for a full list of items that can appear in modules, see https://doc.rust-lang.org/reference/items.html

error: aborting due to 1 previous error

Couldn't compile the test.

Expected output

I would expect the error message to be around the actual problematic line, or with an additional hint saying the error is possibly due to a missing semicolon somewhere.

Meta

rustc --version --verbose:

binary: rustc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-pc-windows-gnu
release: 1.87.0
LLVM version: 20.1.1

rustdoc --version --verbose:

rustdoc 1.87.0 (17067e9ac 2025-05-09)
binary: rustdoc
commit-hash: 17067e9ac6d7ecb70e50f92c1944e545188d2359
commit-date: 2025-05-09
host: x86_64-pc-windows-gnu
release: 1.87.0
LLVM version: 20.1.1

Also reproducible on nightly.

rustc --version --verbose:

rustc 1.89.0-nightly (573a01569 2025-06-12)
binary: rustc
commit-hash: 573a01569000d395498a5f98f916d6e5305ac81a
commit-date: 2025-06-12
host: x86_64-pc-windows-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

rustdoc --version --verbose:

rustdoc 1.89.0-nightly (573a01569 2025-06-12)
binary: rustdoc
commit-hash: 573a01569000d395498a5f98f916d6e5305ac81a
commit-date: 2025-06-12
host: x86_64-pc-windows-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

Reproduce the report by placing the example in src/lib.rs of a new Cargo project and running cargo test --doc with the shown rustc and rustdoc versions. Start by tracing how rustdoc compiles doctests and reports the missing-semicolon case. Done means the diagnostic points near the actual problematic line or adds a useful missing-semicolon hint, with the reproduction covered by a test.