Goals for colcon

A few high level goals are used to guide the overall development.

  • The tool should make building, testing and using multiple packages easy.
  • It should be possible to add support for any kind of build system using extensions. colcon-core only bundles Python support in order to bootstrap itself.
  • It should be possible to build any set of packages without requiring changes to their sources. If necessary missing information can be provided externally.
  • After building packages they must be immediately usable which includes setting up necessary environment variables etc.

Explicitly out of scope

The tool does not aim to address any of the following tasks. Those should be left for other tools to take care of them.

  • Fetch the source of the packages which should be processed by colcon.
  • Install dependencies of the packages which should be processed by colcon.
  • Perform packaging tasks like creating Debian packages.


While these items are specifically not targeted by colcon it is still possible to implement support for any of these features (or helpful functionality to integration with existing tools) in an extension.

Software design

Additionally some software design goals are stated:

  • All the functionality provided should be exposed in a way that it can be reused by other extensions.
  • The separation into multiple Python packages is being used to encourage modularity and loose coupling (Law of Demeter). It is also used to demonstrate extensibility and show that certain features are not “special” but can be contributed externally.
  • Each component should have responsibility over a single part of the software (Single responsibility principle).
  • Each functionality added should follow the principle “you don’t pay for what you don’t use”.