Buck2 New Project

Overview

This skill scaffolds new Buck2 projects with all required boilerplate: BUILD files with proper depot.* shims, PACKAGE files with metadata, SPDX license headers, and language-specific source templates. It saves time and ensures consistency across the monorepo.

Use this skill when:

• Creating a new Rust binary, library, or test crate
• Setting up a new Deno/TypeScript tool under src/tools/
• Starting a new C++ project or library
• Adding a new component to the monorepo that needs its own BUILD file

This skill provides:

• Automated project scaffolding with scripts/new_project.py
• Language-specific templates (Rust, Deno, C++)
• Proper SPDX headers and copyright notices
• Correct use of depot.* shim wrappers
• PACKAGE file with metadata

Quick Start

The fastest way to create a new project:

# Run the scaffolding script
python3 /path/to/skills/buck2-new-project/scripts/new_project.py \
  --type rust_binary \
  --name my-tool \
  --path src/tools/my-tool \
  --description "My awesome new tool" \
  --author "Your Name"

# This creates:
# - src/tools/my-tool/BUILD (with depot.rust_binary())
# - src/tools/my-tool/PACKAGE (with metadata)
# - src/tools/my-tool/src/main.rs (with SPDX headers)

Supported Project Types

• rust_binary - Rust executable with main.rs
• rust_library - Rust library with lib.rs
• deno_binary - Deno/TypeScript tool with main.ts

Creating Different Project Types

Rust Binary

For standalone executables and CLI tools:

python3 scripts/new_project.py \
  --type rust_binary \
  --name build_helper \
  --path src/tools/build-helper \
  --description "A small Buck2 build helper" \
  --author "Austin Seipp"

Generated BUILD file:

load("@root//buck/shims:shims.bzl", depot = "shims")

depot.rust_binary(
    name = "build_helper",
    srcs = glob(["src/**/*.rs"]),
    deps = [
        "third-party//by-name/mi/mimalloc:rust",
    ],
    visibility = ["PUBLIC"],
)

Generated main.rs:

// SPDX-FileCopyrightText: © 2024-2026 Austin Seipp
// SPDX-License-Identifier: Apache-2.0

fn main() {
    println!("Hello from build-helper!");
}

Rust Library

For reusable code libraries:

python3 scripts/new_project.py \
  --type rust_library \
  --name common-utils \
  --path src/lib/common-utils \
  --description "Common utility functions" \
  --author "Austin Seipp"

Generated BUILD file:

load("@root//buck/shims:shims.bzl", depot = "shims")

depot.rust_library(
    name = "common-utils",
    srcs = glob(["src/**/*.rs"]),
    visibility = ["PUBLIC"],
)

Generated lib.rs:

// SPDX-FileCopyrightText: © 2024-2026 Austin Seipp
// SPDX-License-Identifier: Apache-2.0

pub fn example() {
    println!("Example function");
}

Deno Binary

For TypeScript-based tools:

python3 scripts/new_project.py \
  --type deno_binary \
  --name formatter \
  --path src/tools/formatter \
  --description "Code formatting tool" \
  --author "Austin Seipp"

Generated BUILD file:

load("@root//buck/shims:shims.bzl", depot = "shims")
load("@toolchains//deno:defs.bzl", deno = "rules")

deno.binary(
    name = "formatter",
    main = "main.ts",
    permissions = ["read", "write"],
    visibility = ["PUBLIC"],
)

Generated main.ts:

// SPDX-FileCopyrightText: © 2024-2026 Austin Seipp
// SPDX-License-Identifier: Apache-2.0

function main() {
  console.log("Hello from formatter!");
}

if (import.meta.main) {
  main();
}

Understanding Generated Files

BUILD File Structure

All BUILD files follow this pattern:

1. Import shims: load("@root//buck/shims:shims.bzl", depot = "shims")
2. Use depot wrappers: depot.rustbinary() NOT rustbinary()
3. Set visibility: Usually ["PUBLIC"] for reusable components
4. Include dependencies: Always add third-party//by-name/mi/mimalloc:rust for Rust binaries

PACKAGE File Metadata

Generated PACKAGE files include:

load("@root//buck/shims:package.bzl", pkg = "package")

pkg.info(
    copyright = ["© 2024-2026 Austin Seipp"],
    license = "Apache-2.0",
    description = "Fast target determination for Buck2",
    version = "1.0.0",
)

This enables:

• OSV (Open Source Vulnerability) tracking
• License compliance
• Version management
• Documentation generation

SPDX Headers

All source files include mandatory SPDX headers:

// SPDX-FileCopyrightText: © 2024-2026 Austin Seipp
// SPDX-License-Identifier: Apache-2.0

These are required by monorepo policy and enable automated license tracking.

Customizing Generated Projects

Adding Dependencies

After generation, edit the BUILD file to add dependencies:

depot.rust_binary(
    name = "my-tool",
    srcs = glob(["src/**/*.rs"]),
    deps = [
        "third-party//by-name/mi/mimalloc:rust",
        "third-party//clap:clap",  # Add CLI argument parser
        "//src/lib/common-utils",  # Add internal library
    ],
    visibility = ["PUBLIC"],
)

Setting Visibility

Control who can depend on your target:

# Public - anyone can use it
visibility = ["PUBLIC"]

# Private - only this package
visibility = []

# Specific targets
visibility = ["//src/tools/...", "//src/lib/..."]

Adding Tests

Extend the BUILD file with test targets:

depot.rust_test(
    name = "test",
    srcs = glob(["src/**/*.rs"]),
    deps = [":my-tool"],
)

Common Patterns

Multi-Binary Project

Create a project with both a library and binary:

# Create library first
python3 scripts/new_project.py \
  --type rust_library \
  --name myapp \
  --path src/myapp

# Then manually add a binary target to BUILD:
depot.rust_binary(
    name = "myapp-cli",
    srcs = ["src/bin/main.rs"],
    deps = [":myapp", "third-party//by-name/mi/mimalloc:rust"],
)

Tool with Configuration

For tools that need config files:

# Generate base project
python3 scripts/new_project.py --type deno_binary --name tool --path src/tools/tool

# Add config.jsonc manually
echo '{"version": "1.0"}' > src/tools/tool/config.jsonc

# Update BUILD to include config:
deno.binary(
    name = "tool",
    main = "main.ts",
    data = ["config.jsonc"],
    permissions = ["read", "write"],
)

Script Reference

new_project.py Options

--type TYPE           Project type: rust_binary, rust_library, deno_binary
--name NAME           Target name (used in BUILD file)
--path PATH           Directory path relative to repo root
--description DESC    Brief description for PACKAGE metadata
--author AUTHOR       Copyright holder name
--license LICENSE     SPDX license ID (default: Apache-2.0)
--version VERSION     Initial version (default: 1.0.0)
--visibility VIS      Visibility list (default: ["PUBLIC"])

Example Invocations

# Minimal - uses defaults
python3 scripts/new_project.py --type rust_binary --name tool --path src/tools/tool

# Full customization
python3 scripts/new_project.py \
  --type rust_library \
  --name mylib \
  --path src/lib/mylib \
  --description "My awesome library" \
  --author "Jane Doe" \
  --license "MIT" \
  --version "0.1.0" \
  --visibility '["//src/..."]'

# Deno project with specific permissions
python3 scripts/new_project.py \
  --type deno_binary \
  --name webserver \
  --path src/tools/webserver \
  --description "HTTP server tool"

Troubleshooting

"Directory already exists"

The script won't overwrite existing directories. Either:

• Choose a different path
• Remove the existing directory first
• Manually create files in the existing location

"Invalid project type"

Ensure --type is one of: rustbinary, rustlibrary, deno_binary

BUILD file doesn't work

Common issues:

• Forgot to use depot.* shims instead of native rules
• Missing load("@root//buck/shims:shims.bzl", depot = "shims")
• Incorrect visibility syntax (should be list: ["PUBLIC"])

Verify with:

buck2 build //path/to/project:name

Tests aren't found

Tests need explicit targets in BUILD:

depot.rust_test(
    name = "test",
    srcs = glob(["src/**/*.rs"]),
)

Then run:

buck2 test //path/to/project:test

Next Steps After Scaffolding

1. Build the project: buck2 build //path/to/project
2. Add actual implementation: Edit the generated source files
3. Add dependencies: Update BUILD file with required deps
4. Write tests: Add test targets and test files
5. Run tests: buck2 test //path/to/project:test
6. Commit with jj: Follow conventional commit format

jj new -m "feat: add new project"
# Make changes...
jj describe -m "feat(myapp): add initial implementation"
jj commit