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Tycho/Target Platform

< Tycho
Revision as of 09:07, 26 October 2011 by (Talk | contribs) (minor improvements in pomDependencies consider)

The target platform is the set of artifacts from which Tycho resolves the project's dependencies.

Background: OSGi allows to specify dependencies with version ranges and package dependencies (Import-Package). These dependencies (intentionally) do not map to unique artifacts. In order to pick a set of concrete bundles to be used for compilation, test execution, and assembly, Tycho needs a set of candidate artifacts which may be used to match the dependencies. This list of candidate artifacts is called the "target platform". The process of selecting artifacts from the target platform according to the project's dependencies is called "dependency resolution".

There are different ways to define the target platform; the most common ones are repositories with layout=p2, which add entire p2 repositories to the target platform, or target definition files for more fine-grained control.

Which approach should I use for the target platform for my project?

Since there are a few different ways to configure a target platform in Tycho, here are some rule of thumbs for the most common cases:

  1. If you are already using a target file in Eclipse, and that target file only contains location elements with type="InstallableUnit", use that target file for the Tycho build. In all other cases, it is not possible to share the target platform configuration between Tycho and Eclipse.
  2. If you don't care about individual bundles and versions, just configure the needed p2 repositories in the POM and have Tycho pick anything required from these repositories.
  3. If you want control over the which bundles/bundle versions are visible to the build, use a target file.

Target platform configuration

The target platform is defined through POM configuration (see details below). Each module has its own target platform, although with the normal configuration inheritance in Maven, the target platform configurations are usually the same across multiple modules. In case multiple configuration approaches are combined (which should be rarely necessary), the target platform contains the union of the content defined through each approach.

"Repositories with layout p2"

In order allow Tycho to resolve the project dependencies against anything from a specific p2 repository, add that repository in the <repositories> section of the POM. Example:


In terms of the target platform, this means that the entire content of the p2 repositories specified in this way become part of the target platform.

Background: In a normal (i.e. non-Tycho) Maven project, one can configure Maven repositories which can be used by Maven to resolve the project dependencies. While Maven repositories cannot be used directly (see below for an indirect approach), Tycho can use p2 repositories for resolving OSGi dependencies. The p2 repositories need to be marked with layout=p2. (The normal Maven dependency resolution ignores repositories with layout=p2.)

"Target files"

The PDE target definition file format (*.target) allows to select a subset of units (bundles, features, etc.) from one or more p2 repositories. In order to add the content of a target definition file (see "Content" tab of the Target Editor) to the target platform in the Tycho build, configure the target file in the target-platform-configuration build plugin. Example:


The target definition file then needs to be placed in the root of project with the specified GAV.

Note: Tycho has only limited support for target definition files:

  • The location types "Directory", "Installation", and "Features" are not supported.
  • The selection on the Content tab of the Target Editor is ignored, i.e. it is not possible to de-select individual bundles for the Tycho target platform.

"POM dependencies consider"

OSGi bundles from Maven repositories can be added to the target platform in the following way:

  1. Specify a dependency to the OSGi bundle artifact in the POM's <dependencies> section.
  2. Set the configuration parameter pomDependencies=consider on the target-platform-configuration plugin

This configuration has the following effect:

  • First, Maven resolves the GAV dependencies according to the normal Maven rules. This results in a list of artifacts with the specified artifacts and their transitive Maven dependencies.
  • Tycho then considers each of these artifacts for the target platform: if the artifact is an OSGi bundle, it is added to the target platform. Other artifacts are ignored. OSGi bundles which become part of the target platform in this way are then available to resolve the project's OSGi dependencies.

For an example, see the POM of this demo project.

Dependency resolution troubleshooting


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