[tycho-dev] what is the "target platform"?

["Oberlies, Tobias" <tobias.oberlies@xxxxxxx>]

In the discussion about bug 363331 [1], I realized that we have a different understanding about the term "target platform", which makes it really hard to discuss about the actual problem. 

This is how I understand the "target platform" at the example what Tycho does for an eclipse-plugin project:

1. If a target file is specified, the TargetDefinitionResolver resolves the target file
2. ResolutionContextImpl.gatherAvailableInstallableUnits computes the "target platform"
3. P2ResolverImpl.resolveProject resolves project dependencies. The result doesn't have a good name - the best I can think of is "resolved project dependencies"
4. The equinox resolver (don't know the class exactly) takes the resolved project dependencies and computes the class path from this.

IMHO it is very important to distinguish between the "target platform" and dependency resolution, because all packaging types need a "target platform", but not all of them need dependency resolution:
- eclipse-plugin needs dependency resolution because the Equinox resolver (step 4) needs a list of local artifacts (the "resolved project dependencies" - in contrast to the target platform which is only a list of IUs)
- eclipse-feature does not need dependency resolution. The root cause for bug 352081 [2] is that the 0.0.0 replacement is done by taking the latest version from "resolved project dependencies" instead of from the "target platform". Dependency resolution could be done as consistency check (e.g. to prevent the build of a feature which cannot be installed later), but not all tycho users want this (see bug 353399 [3]).
- eclipse-product does not need dependency resolution - the director can directly operate on the "target platform"
- eclipse-repository cannot use the dependency resolution result, if we want to allow more flexible aggregation rules (e.g. multiple versions of bundles)

Does this make sense to you?

Regards
Tobias


[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=363331 : specify additional target platform requirements in pom.xml
[2] https://bugs.eclipse.org/bugs/show_bug.cgi?id=352081 : Handling of version 0.0.0 in feature plugin inclusions
[3] https://bugs.eclipse.org/bugs/show_bug.cgi?id=353399 : Feature require import show warn, not fail.