Currently, nextest doesn't support Rust doctests. This is because doctests are not exposed in stable Rust the way regular test binaries are, and are instead treated as special by cargo test.

One nightly-only fix that might work is to collect doctest executables through -Z unstable-options --persist-doctests. However, this isn't a stable approach so it must be used with care.

Note: You can run cargo test --doc as a separate step from cargo nextest run. This will not incur a performance penalty: cargo nextest run && cargo test --doc will not cause any more builds than a plain cargo test that runs doctests.