Tooling & IDE Support

Starlark Tooling

Developer tools for writing, debugging, and maintaining Starlark code.

Language Servers (LSP)

Language servers provide IDE features like completion, diagnostics, and navigation.

Starpls

Starpls is a standalone Starlark language server.

Features:

Code completion
Go to definition
Find references
Hover documentation
Diagnostics

Installation:

brew install starpls

cargo install starpls

VS Code Setup:

Starpls integrates with VS Code through the vscode-bazel extension (v0.10.0+):

{
  "bazel.lsp.command": "starpls"
}

bazel-lsp

bazel-lsp is based on Facebook’s Starlark language server with Bazel-specific extensions.

VS Code Setup:

{
  "bazel.lsp.command": "bazel-lsp"
}

Buck2 LSP

Buck2 includes a built-in language server for its Starlark dialect.

buck2 lsp

Features:

Full Buck2 API completion
Target navigation
Provider documentation
BXL support

VS Code Setup:

See Buck2 VS Code extension for integration.

Debugging (DAP)

Buck2 DAP

Buck2 provides Debug Adapter Protocol support for stepping through Starlark:

buck2 starlark debug-attach

Features:

Breakpoints
Step in/out/over
Variable inspection
Call stack viewing

VS Code launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "buck2-starlark",
      "request": "attach",
      "name": "Attach to Buck2 Starlark",
      "port": 4567
    }
  ]
}

IDE Extensions

Visual Studio Code

Bazel

Bazel BUILD files + LSP support (starpls or bazel-lsp)

Install

Buck2

Buck2 integration

Install

Kurtosis

Kurtosis Starlark

Install

JetBrains IDEs

Plugin	IDE	Features
Bazel	IntelliJ, CLion	BUILD syntax, completion
Buck	IntelliJ	Buck file support

Neovim

Using nvim-lspconfig:

require('lspconfig').starpls.setup({
  cmd = { 'starpls' },
  filetypes = { 'starlark', 'bzl', 'star' },
})

Or with Mason:

require('mason-lspconfig').setup({
  ensure_installed = { 'starpls' },
})

Formatters

Buildifier

The official formatter for Bazel BUILD files:

# Install
go install github.com/bazelbuild/buildtools/buildifier@latest

# Format
buildifier -r .

# Check only
buildifier -mode=check -r .

Configuration (.buildifier.json):

{
  "version": "6.0.0",
  "lint": "warn",
  "warnings": ["attr-cfg", "attr-license"]
}

Sky Formatter

Sky includes a Starlark formatter:

skyfmt path/to/file.star
skyfmt --check .  # Check without modifying

Linters

Buildifier Lint

Buildifier includes lint checks:

buildifier -lint=warn path/to/BUILD.bazel

Common warnings:

load-on-top - Load statements should be first
same-origin-load - Combine loads from same file
unused-variable - Remove unused variables

Sky Lint

Sky provides additional Starlark-specific checks:

skylint path/to/file.star

Checks include:

Unused imports and variables
Naming conventions
Performance issues
Security concerns

Testing

Skytest

Sky’s test runner:

skytest path/to/test.star

Test file format:

load("math.star", "add", "multiply")

def test_add():
    assert_eq(add(1, 2), 3)
    assert_eq(add(-1, 1), 0)

def test_multiply():
    assert_eq(multiply(2, 3), 6)
    assert_eq(multiply(0, 5), 0)

unittest.bzl

Bazel Skylib testing for Bazel rules:

load("@bazel_skylib//lib:unittest.bzl", "asserts", "unittest")

def _add_test_impl(ctx):
    env = unittest.begin(ctx)
    asserts.equals(env, 3, add(1, 2))
    return unittest.end(env)

add_test = unittest.make(_add_test_impl)

REPL

Sky REPL

Interactive Starlark shell:

skyrepl

>>> x = [1, 2, 3]
>>> [i * 2 for i in x]
[2, 4, 6]
>>> def greet(name):
...     return "Hello, " + name
...
>>> greet("World")
"Hello, World"

starlark-go REPL

go run go.starlark.net/cmd/starlark

Buck2 REPL

buck2 starlark repl

Documentation Generators

Stardoc

Bazel’s documentation generator:

load("@io_bazel_stardoc//stardoc:stardoc.bzl", "stardoc")

stardoc(
    name = "my_rules_docs",
    input = "my_rules.bzl",
    out = "my_rules.md",
)

Sky Doc

Sky’s documentation generator:

skydoc path/to/module.star -o docs/

Generates markdown from docstrings:

def build_target(name, srcs, deps = []):
    """Creates a build target.

    Args:
        name: Target name (must be unique)
        srcs: Source files to compile
        deps: Optional dependencies

    Returns:
        A target object
    """
    ...

Recommended Setup

Install Starpls
Terminal window
```
brew install starpls
```
Configure VS Code

Install the vscode-bazel extension and configure:
```
{
  "bazel.lsp.command": "starpls"
}
```

Install Buildifier

go install github.com/bazelbuild/buildtools/buildifier@latest

Configure Format on Save

{
  "[starlark]": {
    "editor.formatOnSave": true,
    "editor.defaultFormatter": "BazelBuild.vscode-bazel"
  }
}

Set Up Pre-commit Hook

repos:
  - repo: https://github.com/keith/pre-commit-buildifier
    rev: 6.4.0
    hooks:
      - id: buildifier
      - id: buildifier-lint

Tooling Comparison

Tool	starlark-rust	starlark-go	starlark-java
LSP	✅ Built-in	⚠️ Starpls	⚠️ Starpls
DAP	✅ Built-in	❌	❌
REPL	✅	✅	❌
Formatter	✅ Buildifier	✅ Buildifier	✅ Buildifier
Linter	✅ Buildifier	✅ Buildifier	✅ Buildifier