pola-rs/polars · error

CARGO_MANIFEST_DIR not set

Error message

CARGO_MANIFEST_DIR not set

What it means

The test helper get_file_path panics via expect() because the CARGO_MANIFEST_DIR environment variable is not set. This variable is set by cargo during `cargo test` but is absent when tests run through other harnesses or environments. It is used to locate the sample foods1.ipc file relative to the crate.

Solutions

1. Run the tests via `cargo test -p polars-arrow` so cargo sets CARGO_MANIFEST_DIR automatically.
2. If invoking the binary directly, export CARGO_MANIFEST_DIR=<path to crates/polars-arrow> before running.
3. Replace the env lookup in the test with a compile-time path such as env!("CARGO_MANIFEST_DIR") or an absolute path fixture.

Example fix

// before
let polars_arrow = std::env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set");
// after
let polars_arrow = env!("CARGO_MANIFEST_DIR");

if std::env::var("CARGO_MANIFEST_DIR").is_err() {
    panic!("Run tests via `cargo test` or set CARGO_MANIFEST_DIR to the polars-arrow crate path");
}

When it happens

Trigger: Running the polars-arrow IPC tests (test_file_flight_simple, test_file_flight_amortized) outside of a cargo-managed invocation, e.g. via a custom test runner, IDE debugger, or a stripped environment where std::env::var("CARGO_MANIFEST_DIR") returns Err.

Common situations: Running tests through tools that sanitize env vars (docker with minimal env, `env -i`), executing the compiled test binary directly instead of `cargo test`, or CI systems that invoke the test executable without cargo.

Understand the failure class

Background: "environment variable is not set" and "Missing keys in environment" errors: what missing required env var messages mean and how to fix them — this error's family across 28 libraries.

Related errors

• {}
• {0}
• activate dtype
• activate 'dtype-array'
• activate dtype-categorical to convert dictionary arrays

AI-assisted analysis of pola-rs/polars@fe841f959e (2026-09-18). Data as JSON: /api/errors/9c181163af06bfdf. Report an issue: GitHub.

Appendix: source

Thrown at crates/polars-arrow/src/io/ipc/read/flight.rs:417

            if option_recordbatch.is_some() {
                return Ok(option_recordbatch);
            }
        }
        Ok(None)
    }
}

#[cfg(test)]
mod test {
    use std::path::{Path, PathBuf};

    use tokio::fs::File;

    use super::*;
    use crate::record_batch::RecordBatch;

    fn get_file_path() -> PathBuf {
        let polars_arrow = std::env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set");
        Path::new(&polars_arrow).join("../../py-polars/tests/unit/io/files/foods1.ipc")
    }

    fn read_file(path: &Path) -> RecordBatch {
        let mut file = std::fs::File::open(path).unwrap();
        let md = crate::io::ipc::read::read_file_metadata(&mut file).unwrap();
        let mut ipc_reader = crate::io::ipc::read::FileReader::new(&mut file, md, None, None);
        ipc_reader.next().unwrap().unwrap()
    }

    #[tokio::test]
    async fn test_file_flight_simple() {
        let path = &get_file_path();
        let mut file = tokio::fs::File::open(path).await.unwrap();
        let stream = into_flight_stream(&mut file).await.unwrap();

        let mut c = FlightstreamConsumer::new(Box::pin(stream)).await.unwrap();
        let b = c.next_batch().await.unwrap().unwrap();

View on GitHub (pinned to fe841f959e)