Thomas Watson created FELIX-5601:
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Summary: issues resolving with substitutable exports when the
export is the last available provider
Key: FELIX-5601
URL: https://issues.apache.org/jira/browse/FELIX-5601
Project: Felix
Issue Type: Bug
Components: Resolver
Reporter: Thomas Watson
Assignee: Thomas Watson
Substitutable exports that are used by other exported packages can cause a case
where a valid solution cannot be found when one exists. The issue only can
occur when a substitutable export is the only valid candidate left for a
resources mandatory requirement and the resolver decides to permute the
substitutable requirement becaused of a used blame. Something like the
following resources
resource A1
provides pkg X v1
provides pkg Y v1 uses->X
provides pkg Z v1 uses->Y
resource A2
provides pkg X v2
provides pkg Y v2 uses->X
provides pkg Z v2 uses->Y
import pkg X v[2,4)
import pkg Y v[2,4)
import pkg Z v[2,4)
resource A3
provides pkg X v3
provides pkg Y v3 uses->X
provides pkg Z v3 uses->Y
import pkg X v[2,4)
import pkg Y v[2,4)
import pkg Z v[2,4)
resource B1
provides pkg W v1 uses->Z
import pkg Z v[1,4)
resource C1
imports pkg X v[3,4)
Resolve all resources A1, A2, A3, B1, C1 as mandatory resources. This will
result in resolution error for B1 because it is exposed to two versions of X
through two uses blame chains. The reason this fails is because the resolver
first chooses to permute the substitutable requirement from A3 for X which
causes X v3 to no longer be available for C1 to import. This causes an error
and the permutation fails and all other permutations based off that permutation
will be ignored. If instead the resolver would not permute the requirement for
X from A3 the resolver would find a valid solution.
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