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
Correctly handles fixture overriding and hierarchies
LSP spec compliant: Always includes the current position in results

📚 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

Choose your preferred installation method:

📦 PyPI (Recommended)

The easiest way to install for Python projects:

# Using uv (recommended)
uv tool install pytest-language-server

# Or with pip
pip install pytest-language-server

# Or with pipx (isolated environment)
pipx install pytest-language-server

🍺 Homebrew (macOS/Linux)

Install via Homebrew for system-wide availability:

brew install bellini666/tap/pytest-language-server

To add the tap first:

brew tap bellini666/tap https://github.com/bellini666/pytest-language-server
brew install pytest-language-server

🦀 Cargo (Rust)

Install from crates.io if you have Rust installed:

cargo install pytest-language-server

📥 Pre-built Binaries

Download pre-built binaries from the GitHub Releases page.

Available for:

Linux: x86_64, aarch64, armv7 (glibc and musl)
macOS: Intel and Apple Silicon
Windows: x64 and x86

🔨 From Source

Build from source for development or customization:

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,
}

Zed

Install the extension from the extensions marketplace:

Open Zed
Open the command palette (Cmd+Shift+P / Ctrl+Shift+P)
Search for "zed: extensions"
Search for "pytest Language Server"
Click "Install"

The extension will automatically detect pytest-language-server if it's in your PATH.

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:

Checks for .venv/, venv/, or env/ in your project root
Falls back to $VIRTUAL_ENV environment variable
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:

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

Fixture Overriding

The LSP correctly handles complex fixture overriding scenarios:

# conftest.py (parent)
@pytest.fixture
def cli_runner():
    return "parent runner"

# tests/conftest.py (child)
@pytest.fixture
def cli_runner(cli_runner):  # Overrides parent
    return cli_runner  # Uses parent

# tests/test_example.py
def test_example(cli_runner):  # Uses child
    pass

When using find-references:

Clicking on the function name def cli_runner(...) shows references to the child fixture
Clicking on the parameter cli_runner(cli_runner) shows references to the parent fixture
Character-position aware to distinguish between the two

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 1.83+ (2021 edition)
Python 3.10+ (for testing)

Building

cargo build --release

Running Tests

cargo test

Logging During Development

RUST_LOG=debug cargo run

Security

Security is a priority. This project includes:

Automated dependency vulnerability scanning (cargo-audit)
License compliance checking (cargo-deny)
Daily security audits in CI/CD
Dependency review on pull requests
Pre-commit security hooks

See SECURITY.md for our security policy and how to report vulnerabilities.

Contributing

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

Development Setup

Install pre-commit hooks:
```
pre-commit install
```
Run security checks locally:
```
cargo audit
cargo clippy
cargo test
```

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.

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

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

pytest-language-server 0.4.0