pytest-language-server 0.1.0

A blazingly fast Language Server Protocol implementation for pytest

pytest-language-server 🔥

Shamelessly vibed into existence 🤖✨

This entire LSP implementation was built from scratch in a single AI-assisted coding session. No template. No boilerplate. Just pure vibes and Rust. That's right - a complete, working Language Server Protocol implementation for pytest, vibed into reality through the power of modern AI tooling. Even this message about vibing was vibed into existence.

A blazingly fast Language Server Protocol (LSP) implementation for pytest, built with Rust.

Features

🎯 Go to Definition

Jump directly to fixture definitions from anywhere they're used:

• Local fixtures in the same file
• Fixtures in conftest.py files
• Third-party fixtures from pytest plugins (pytest-mock, pytest-asyncio, etc.)
• Respects pytest's fixture shadowing/priority rules

🔍 Find References

Find all usages of a fixture across your entire test suite:

• Works from fixture definitions or usage sites
• Character-position aware (distinguishes between fixture name and parameters)
• Shows references in all test files

📚 Hover Documentation

View fixture information on hover:

• Fixture signature
• Source file location
• Docstring (with proper formatting and dedenting)
• Markdown support in docstrings

⚡️ Performance

Built with Rust for maximum performance:

• Fast workspace scanning with concurrent file processing
• Efficient AST parsing using rustpython-parser
• Lock-free data structures with DashMap
• Minimal memory footprint

Installation

From PyPI (Recommended)

Using uv (recommended):

uv tool install pytest-language-server

Or with pip:

pip install pytest-language-server

From Crates.io

cargo install pytest-language-server

From Source

git clone https://github.com/bellini666/pytest-language-server
cd pytest-language-server
cargo build --release

The binary will be at target/release/pytest-language-server.

Setup

Neovim (with nvim-lspconfig)

require'lspconfig'.pytest_lsp.setup{
  cmd = { "pytest-language-server" },
  filetypes = { "python" },
  root_dir = function(fname)
    return require'lspconfig'.util.root_pattern('pyproject.toml', 'setup.py', 'setup.cfg', 'pytest.ini')(fname)
  end,
}

VS Code

Install the extension from the marketplace (coming soon) or configure manually:

{
  "pytest-language-server.enable": true,
  "pytest-language-server.path": "pytest-language-server"
}

Other Editors

Any editor with LSP support can use pytest-language-server. Configure it to run the pytest-language-server command.

Configuration

Logging

Control log verbosity with the RUST_LOG environment variable:

# Minimal logging (default)
RUST_LOG=warn pytest-language-server

# Info level
RUST_LOG=info pytest-language-server

# Debug level (verbose)
RUST_LOG=debug pytest-language-server

# Trace level (very verbose)
RUST_LOG=trace pytest-language-server

Logs are written to stderr, so they won't interfere with LSP communication.

Virtual Environment Detection

The server automatically detects your Python virtual environment:

1. Checks for .venv/, venv/, or env/ in your project root
2. Falls back to $VIRTUAL_ENV environment variable
3. Scans third-party pytest plugins for fixtures

Supported Fixture Patterns

Decorator Style

@pytest.fixture
def my_fixture():
    """Fixture docstring."""
    return 42

Assignment Style (pytest-mock)

mocker = pytest.fixture()(_mocker)

Async Fixtures

@pytest.fixture
async def async_fixture():
    return await some_async_operation()

Fixture Dependencies

@pytest.fixture
def fixture_a():
    return "a"

@pytest.fixture
def fixture_b(fixture_a):  # Go to definition works on fixture_a
    return fixture_a + "b"

Fixture Priority Rules

pytest-language-server correctly implements pytest's fixture shadowing rules:

1. Same file: Fixtures defined in the same file have highest priority
2. Closest conftest.py: Searches parent directories for conftest.py files
3. Virtual environment: Third-party plugin fixtures

Supported Third-Party Fixtures

Automatically discovers fixtures from popular pytest plugins:

• pytest-mock: mocker, class_mocker
• pytest-asyncio: event_loop
• pytest-django: Database fixtures
• pytest-cov: Coverage fixtures
• And any other pytest plugin in your environment

Architecture

• Language: Rust 🦀
• LSP Framework: tower-lsp
• Parser: rustpython-parser
• Concurrency: tokio async runtime
• Data Structures: DashMap for lock-free concurrent access

Development

Prerequisites

• Rust 1.70+ (2021 edition)
• Python 3.8+ (for testing)

Building

cargo build --release

Running Tests

cargo test

Logging During Development

RUST_LOG=debug cargo run

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

MIT License - see LICENSE file for details.

Acknowledgments

Built with:

• tower-lsp - LSP framework
• rustpython-parser - Python AST parsing
• tokio - Async runtime

Special thanks to the pytest team for creating such an amazing testing framework.

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Made with ❤️ and Rust. Shamelessly vibed into existence. Blazingly fast. 🔥

When you need a pytest LSP and the vibes are just right. ✨