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

Many languages organize code in a package hierarchy, so that the relative location of a source file on the filesystem corresponds to a logical package name. The directories that correspond to the roots of the language's package hierarchy are referred to as source roots. These are the filesystem locations from which import paths are computed.

For example, if your Python code lives under src/python, then import myorg.myproject.app will import the code in src/python/myorg/myproject/app.py.

In simple cases the root of the repository itself might be your only source root. But in many other cases the code is organized so that the source root is nested under some directory such as src/ or src/<language name>.

To work correctly, Pants needs to know about the source roots in your repo. By default, given a source file path, Pants will treat the longest path prefix that ends in src, src/python, or src/py as its source root, falling back to the repo root itself if no such prefix is found.

If your project has a different structure, see Source roots for how to configure them, and for examples of different project structures you can use Pants with.

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Golang projects can skip this step

Golang projects already use go.mod to indicate 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",
]

See here for a list of available backends.

4. Generate BUILD files

You use files named BUILD to inform Pants about the location of your code, and to provide metadata about it. A BUILD file is typically located adjacent to the code it describes. Unlike many other systems, Pants BUILD files are usually very succinct, as most metadata is either inferred from static analysis, assumed from sensible defaults, or generated for you.

Once you have enabled the backends for the language(s) you'd like to use, run ./pants tailor to generate an initial set of BUILD files.


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