Distinguish between dependency resolution and scope

[laeubi]

Currently the dependency scope is used in the target location as follows:

• if none (or empty) is give no dependencies are resolved
• if given, dependencies are resolved and filtered for the given scope (at least in the latest version)
• if a dependency is a pom dependency and no scope is given only direct dependencies are consider otherwise all dependencies

While implementing that feature in tycho and trying to get both in sync I noticed that this is maybe not enough and it was at other places noticed by @HannesWell that it might not fit the expectation or confuse users.

I therefore like to propose the following adjustments that would better fit the maven model and the actual dependency resolution process:

• the scope is only used to filter the (possibly empty) list of dependencies, if it is empty or not given it is assumed to be compile scope (that's how maven actually handle it)
• add a new includeDependencyDepth that could take the value NONE (no dependencies included), DIRECT (only direct dependency child's are included), INFINITE (all transitive dependencies are included)
• for pom dependencies NONE is consider the same as DIRECT

The good thing is that we can simply assume that if includeDependencyDepth is missing and includeDependencyScope is specified we can assume INFINITE and thus would be able to be backward compatible to the existing format with auto-upgrading from the previous format.

FYI @vogella

Comments are welcome, if there are no concerns I'd like to get this feature into the upcoming 2.6.x release of tycho and prepare a patch for m2e as well.

[vogella]

Current approach for the Eclipse platform is described in https://bugs.eclipse.org/bugs/show_bug.cgi?id=510186. Also see https://bugs.eclipse.org/bugs/show_bug.cgi?id=570685 for the report that the SWT artifacts seems not working if sourced from Maven central.

[laeubi]

@vogella was this intended for another discussion?

[HannesWell]

That's a good proposal which would make the dependency-inclusion more powerful and more clear. So +1 from me.

In case of absent includeDependencyScope the automatic conversion would change it the properties to
includeDependencyScope = Compile/absent and includeDependencyDepth = NONE?

Or would the case of absent includeDependencyScope and includeDependencyDepth still be allowed and just be interpreted as includeDependencyDepth = NONE? I think having explicit values (at least for the depth) would be more clear.
At least we cannot mimic the Maven behaviour here, where the default that is is used in case of absence is scope=compile and depth=infinite because that would not be backward compatible.

[laeubi]

Missing values will be interpreted as includeDependencyDepth = NONE and includeDependencyScope = Compile