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-ast` 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_ast.rs:22

use anyhow::Result;

use ruff_linter::source_kind::SourceKind;
use ruff_python_ast::{PySourceType, SourceType};
use ruff_python_parser::{ParseOptions, parse};

#[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 python_ast =
        parse(source_kind.source_code(), ParseOptions::from(source_type))?.into_syntax();
    println!("{python_ast:#?}");
    Ok(())
}

View on GitHub (pinned to 672bb4edf0)

Solutions

1. Copy or rename the file to a `.py` (or `.pyi` for stubs) extension and rerun
2. If you need the AST of unusual inputs, pipe the source through a temporary .py file

Example fix

# before
cargo dev print-ast snippet

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

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

When it happens

Trigger: Running `cargo dev print-ast snippet.pyx`, `cargo dev print-ast script` (no extension), or any non-.py/.pyi path.

Common situations: Inspecting scratch files saved without extensions; .pyi-mislabeled stubs; test fixtures with custom suffixes such as .pyi.txt.

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/56b3fa2ef7894603. Report an issue: GitHub.