| [eclipse-dev] IAccessRule and transitive exports |
I have an interesting problem that I’m working on with a custom classpath container (part of Bndtools).
My workspace has:
A jar library osgi.core, which has a set of public packages;
Project A, which has osgi.core as its sole dependency, and no classes of its own, but embeds package org.osgi.framework as part of its public API and org.osgi.util.tracker as a non-public package.
Project B, which also has osgi.core as a dependency, but which doesn't embed any packages from it.
What I want is for the osgi.core library to be made visible to transitive dependencies, but only the relevant subset of packages that is referenced by the "in-transit" project. Ie, suppose project D has only project A on its build path - it should be able
to see package org.osgi.framework without warnings, org.osgi.util.tracker with warnings, and all other packages of osgi.core should generate errors. Likewise, if it has project B on its build path, it shouldn't be able to see any of the packages of osgi.core
without generating an error.
I have implemented a scheme that works fine using Eclipse 2020-06:
-Project A's custom container adds osgi.core using JavaCore.newLibraryEntry(), with the export flag set to "true". Likewise for project B.
-When Project D has Project A as the sole entry on its build path, the container adds it using JavaCore.newProjectEntry(), export set to "true", combine access rules set to "true", org.osgi.framework with an IAccessRule of K_ACCESSIBLE, org.osgi.util.tracker
with K_DISCOURAGED | K_IGNORE_IF_BETTER, and a final default rule of "**" with K_NON_ACCESSIBLE | K_IGNORE_IF_BETTER. This produces the expected result - classes in project D can see classes in org.osgi.framework without warning, can see org.osgi.util.tracker
with a warning, and an attempt to access any other package in osgi.core generates an error.
-Likewise, when Project D has Project A as the sole entry, the container adds it with JavaCore.newProjectEntry(), export true, combine rules true, and a single default rule of "**" with K_NON_ACCESSIBLE | K_IGNORE_IF_BETTER. This too works as expected.
What is not expected is when I try to add both project A and B to the build path at the same time. In this case, instead of the visibility into the transitive dependency osgi.core being determined by the most lenient access rules (which is what I understood
"IGNORE_IF_BETTER" to mean), it is determined by the access rules of whichever dependency appears first on the build path. Ie, if project A comes first, the classes of project D can see org.osgi.framework and (with a warning) org.osgi.util.tracker - however,
if project B comes first on the build path, then none of the org.osgi packages is osgi.core are visible to project D.
Am I missing something here? Have I misconfigured it? Does IGNORE_IF_BETTER not work the way that I expect it? Or is there a bug?
Any light that anyone could shed on this would be much appreciated.
Blessings,
Chief Executive Officer
Greek Welfare Centre SA
St Philothei
Greek Orthodox Archdiocese of Australia
213 Henley Beach Road
TORRENSVILLE SA 5031
Phone: (08) 8212 5100