astral-sh/ruff · error

Could not determine source kind for file: {}

Error message

Could not determine source kind for file: {}

What it means

`cargo dev print-tokens` loads the given file through SourceKind::from_path, which only recognizes `.py` and `.pyi` extensions; any other suffix (or no suffix) returns None and this error is raised.

Source

Thrown at crates/ruff_dev/src/print_tokens.rs:22

use anyhow::Result;

use ruff_linter::linter::parse_unchecked_source;
use ruff_linter::source_kind::SourceKind;
use ruff_python_ast::{PySourceType, PythonVersion, SourceType};

#[derive(clap::Args)]
pub(crate) struct Args {
    /// Python file for which to generate the AST.
    #[arg(required = true)]
    file: PathBuf,
}

pub(crate) fn main(args: &Args) -> Result<()> {
    let source_type = PySourceType::from(&args.file);
    let source_kind = SourceKind::from_path(&args.file, SourceType::Python(source_type))?
        .ok_or_else(|| {
            anyhow::anyhow!(
                "Could not determine source kind for file: {}",
                args.file.display()
            )
        })?;
    let parsed = parse_unchecked_source(&source_kind, source_type, PythonVersion::default());
    for token in parsed.tokens() {
        println!("{token:#?}");
    }
    Ok(())
}

View on GitHub (pinned to 672bb4edf0)

Solutions

1. Copy or rename the file to `.py` (or `.pyi`) and rerun
2. Feed the content via a temporary .py file when the original name must stay unchanged

Example fix

# before
cargo dev print-tokens tokens

# after
cp tokens /tmp/tokens.py && cargo dev print-tokens /tmp/tokens.py

case "$f" in
  *.py|*.pyi) cargo dev print-tokens "$f" ;;
  *) echo "expected a .py or .pyi file: $f" >&2; exit 1 ;;
esac

When it happens

Trigger: Running `cargo dev print-tokens lexer.txt` or any path that does not end in .py/.pyi.

Common situations: Tokenizing scratch files without extensions or with renamed suffixes; fixtures saved as .python or .src.

Related errors

• Could not determine source kind for file: {}
• Unknown option: {key}
• The `--range` option is only supported when formatting a sin
• {flag} <reason> cannot contain newline characters
• Unsupported serialization format for statistics: {:?}

AI-assisted analysis of astral-sh/ruff@672bb4edf0 (2026-08-16). Data as JSON: /api/errors/71ecc7553c5a1753. Report an issue: GitHub.