Hello Pants Build

Posted September 2014

As code bases grow, they become increasingly difficult to work with. Builds get ever slower and existing tooling doesn’t scale. One solution is to keep splitting the code into more and more independent repositories. However, as growth continues you end up with hundreds of free-floating codebases with hard-to-manage dependencies. This makes it hard to discover, navigate and share code which can impact developer productivity.

Another solution is to have a single large, unified code base. We’ve found that this promotes better engineering team cohesion and collaboration which results in greater productivity and happiness. However, tooling for such structured code bases has been lacking which is why we developed Pants, an open source build system written in Python.

Pants models code modules (known as “targets”) and their dependencies in BUILD files—in a manner similar to Google's internal build system. This allows it to only build the parts of the codebase you actually need, ignoring the rest of the code. This is a key requirement for scaling large, unified code bases.

Pants started out in 2010 as an internal tool at Twitter and was originally just a frontend to generate build.xml files for the Ant build tool, hence the name (a contraction of “Python Ant”). Pants grew in capability and complexity, and became the build tool for the twitter/commons open source libraries, and hence became open source itself.

In 2012, Foursquare began using Pants internally, and Foursquare engineers picked up the Pants development mantle, adding Scala support, build artifact caching and many other features.

Since then several other engineering teams, including those at Urban Compass and Oscar, have integrated Pants into their codebases. Most recently, Square began to use Pants and has also contributed significantly to its development.

As a result, Pants is a true independent open source project with collaborators across companies and a growing development community. It now lives in a standalone repo at https://github.com/pantsbuild/pants.

Among Pants’s current strengths are:

  • Builds Java, Scala, and Python.
  • Adding support for new languages is straightforward.
  • Supports code generation: thrift, protocol buffers, custom code generators.
  • Resolves external JVM and Python dependencies.
  • Runs tests.
  • Spawns Python and Scala REPLs with appropriate load paths.
  • Creates deployable packages.
  • Scales to large repos with many interdependent modules.
  • Designed for incremental builds.
  • Support for local and distributed caching.
  • Especially fast for Scala builds, compared to alternatives.
  • Builds standalone python executables (PEX files)
  • Has a plugin system to add custom features and override stock behavior.
  • Runs on Linux and Mac OS X.

Since moving Pants to its own GitHub organization, our commit rate has grown and we’ve welcomed more committers to the project.

If your codebase is growing beyond your toolchain’s ability to scale, but you’re reluctant to split it up, you might want to give Pants a try. It may be of particular interest if you have complex dependencies, generated code and custom build steps.

Pants is still a young and evolving open source project. We constantly strive to make it easier to use. If you’re interested in using or learning from Pants, our advice is to reach out to the community on the developer mailing list and follow @pantsbuild on Twitter for updates.

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