Managing multiple languages in a monorepo can be a nightmare. Tools, build systems, dependencies, and environments often conflict when Java, Python, and Go coexist. Enter Pants — a fast, scalable, and user-friendly build system built for polyglot monorepos.

In this article, we’ll explore how Pants supports multi-language development across Java, Python, and Go, how it improves developer workflows, and how to get started with real-world examples.

Why Use Pants in a Polyglot Repository?

Traditional build systems like Maven (Java), pip/venv (Python), or go build (Go) aren’t designed for managing multiple languages under one roof. Pants solves this by:

• Supporting multi-language builds natively
• Providing a unified CLI for building, testing, linting, and formatting
• Offering fine-grained caching, parallelism, and remote execution
• Integrating with popular tools like black, flake8, pytest, javac, and go build

Supported Languages and Toolchains

As of Pants 2.20+, these are officially supported:

You can mix and match these in a single monorepo with minimal config changes.

Initializing Pants in Your Repository

Step 1: Bootstrap Pants

curl -fsSL https://static.pantsbuild.org/setup/pants | bash

[GLOBAL]
backend_packages = [
 "pants.backend.python",
 "pants.backend.java",
 "pants.backend.go",
]

pants_version = "2.20.0"

Step 3: Create BUILD files

Pants uses BUILD or BUILD.<lang> files to declare targets. Here’s how you do it for each language:

Python Example

File structure:

src/
└── python/
 └── mylib/
 ├── __init__.py
 └── utils.py

BUILD file (src/python/mylib/BUILD):

python_sources()

You can test with:

./pants test src/python/mylib::

Java Example

File structure:

src/
└── java/
 └── com/
 └── example/
 └── HelloWorld.java

BUILD file (src/java/com/example/BUILD):

java_sources()

Compile or run tests:

./pants compile src/java/com/example::

Go Example

File structure:

src/
└── go/
 └── example/
 └── main.go

BUILD file (src/go/example/BUILD):

go_package()
go_binary(name="main", source="main.go")

./pants run src/go/example:main

Cross-Language Interop

While Pants doesn’t handle language interop directly (e.g., calling Go from Java), it allows independent language pipelines to co-exist cleanly. Teams can:

• Share a monorepo
• Define per-language CI steps with a shared CLI
• Cache builds and tests independently
• Use Pants’s dependency inference to reduce boilerplate

Developer Benefits

✅ Unified Tooling

No need to install Maven, pipenv, or Go directly — Pants manages the environments behind the scenes.

✅ Incremental & Cached Builds

Only what changes gets rebuilt or retested, thanks to Pants’s smart fingerprinting.

✅ IDE Support

Use ./pants export to generate project files for IntelliJ, VSCode, etc.

✅ First-Class Python Support

Many multi-language tools fall short with Python — Pants offers full support for Python packaging, testing, linting, and even lockfile generation.

Example: Adding a Python Test for a Java Build Artifact

You can structure your repo so Python tests or tools validate a Java CLI binary:

# Export Java binary
./pants package src/java/com/example:hello-cli

# Call it from Python using subprocess in integration tests

This is helpful for integration testing or end-to-end validation workflows.

Running Tests for All Languages

Run all tests across all languages with:

./pants test ::

Or filter per language:

./pants test 'src/python::'
./pants test 'src/java::'
./pants test 'src/go::'

Sample Project Layout

repo/
├── pants.toml
├── src/
│ ├── python/
│ │ └── ...
│ ├── java/
│ │ └── ...
│ └── go/
│ └── ...
└── BUILD files in each subdir

Conclusion

Pants makes it easy to manage Java, Python, and Go in a single repository without forcing developers into language silos. With smart build caching, unified tooling, and deep support for popular workflows, it’s a solid foundation for polyglot teams embracing monorepo architecture.

References

• Pants Build Official Site
• GitHub: pantsbuild/pants