doctests are not run when specifying a target

[tyilo]

Steps to reproduce:

cd /tmp
cargo new --lib doctest-test
cd doctest-test

Add a doctest to src/lib.rs to:

/// ```
/// use doctest_test::add;
///
/// assert_eq!(add(1, 2), 3);
/// ```
pub fn add(left: u64, right: u64) -> u64 {
    left + right
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);
    }
}

Run the tests with different targets:

$ cargo test
cargo test
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.01s
     Running unittests src/lib.rs (target/debug/deps/doctest_test-80cbe61ba5d23d25)

running 1 test
test tests::it_works ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

   Doc-tests doctest_test

running 1 test
test src/lib.rs - add (line 1) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

$ cargo test --target x86_64-unknown-linux-musl
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running unittests src/lib.rs (target/x86_64-unknown-linux-musl/debug/deps/doctest_test-414700a1c2498589)

running 1 test
test tests::it_works ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

$ cargo test --target i686-unknown-linux-gnu
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running unittests src/lib.rs (target/i686-unknown-linux-gnu/debug/deps/doctest_test-00139adbea66aca7)

running 1 test
test tests::it_works ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

As you can see only the normal test is run, but not the doctest.

Meta

This happens in both the current stable and nightly version.

rustc --version --verbose:

rustc 1.86.0 (05f9846f8 2025-03-31)
binary: rustc
commit-hash: 05f9846f893b09a1be1fc8560e33fc3c815cfecb
commit-date: 2025-03-31
host: x86_64-unknown-linux-gnu
release: 1.86.0
LLVM version: 19.1.7

rustc +nightly --version --verbose:

rustc 1.89.0-nightly (414482f6a 2025-05-13)
binary: rustc
commit-hash: 414482f6a0d4e7290f614300581a0b55442552a3
commit-date: 2025-05-13
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4

[ehuss]

Thanks for the report! This is a known issue, which hopefully will get resolved soon via rust-lang/cargo#15462. Closing as a duplicate of rust-lang/cargo#7040.