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Initial configuration

Creating the initial pants.toml config file.

Pants has a robust options system, allowing you to configure hundreds of options. Every Pants option can be set via a command-line flag, an environment variable, or, most commonly, a config file.

The options system is described in detail here. This page will set up your initial Pants config file.

1. Create pants.toml

Pants configuration lives in a file called pants.toml in the root of the repo. This file uses the TOML format.

If you haven't yet, create a pants.toml file:

[GLOBAL]
pants_version = "$PANTS_VERSION"

where $PANTS_VERSION is the version of Pants you want to pin your repo to. When you'd like to upgrade Pants, edit pants_version and the ./pants script will self-update on the next run.

2. Configure source roots

Some project layouts use top-level folders for namespace purposes, but have the code live underneath. However, the code's imports will ignore these top-level folders, thanks to mechanisms like the $PYTHONPATH and the JVM classpath. For example, to import the file src/my_project/app.py, many projects use import my_project.app, rather than import src.my_project.app. Source roots are how Pants understands these imports.

By default, Pants recognizes having no source root, or having src, src/python, or src/py as source roots. If your project has a different structure, see Source roots for how to configure them, and for examples of different project structures with Pants.

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Golang projects can skip this step

Golang projects already use go.mod as an equivalent to "source roots".

3. Enable backends

Most Pants functionality is provided via pluggable backends, which are activated by adding to the [GLOBAL].backend_packages option like this:

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

4. Generate BUILD files

Finally, once you have enabled the backends for the language(s) you'd like to use, run ./pants tailor to generate BUILD files for Pants to know which code to operate on.


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