ST6RI-925 Problem with deriveTypeFeatureMembership (KERML11-191)

[seidewitz]

This PR proactively implements the resolution to the following issue, which the KerML 1.1 RTF has elevated to be a "blocker" issue.

• KERML11-191 Problem with deriveTypeFeatureMembership

Background

Currently (as of KerML 1.0), the OCL for deriveTypeFeatureMembership is

featureMembership = ownedFeatureMembership->union(
    inheritedMembership->selectByKind(FeatureMembership))

The intent here is clearly to not include imported feature memberships. The problem is that inheritedMembership does include imported feature memberships from supertypes. Since Type::feature is derived from featureMembership, this means that a type may get features that are not owned features of any of its supertypes, which may have owning types incompatible with the inheriting type.

Overview

The proposed change to the OCL is to simply further filter the inherited feature memberships with select(mem | self.specializes(mem.owningType)). The implementation in Type_featureMembership_SettingDelegate could be similarly updated with such a filter. However, doing this naively has a notable negative effect on performance. This is because specializes is implemented by computing the allSupertypes transitive closure and then checking against that. And the set of allSupertypes gets recomputed on each call to specializes.

The performance problem can be mitigated by computing allSupertypes once, outside the filtering loop, and then using allSupertypes.contains rather than this.specializes. With this change (and caching), the performance is essentially effected by the change.

Changes

• Type_featureMembership_SettingDelegate – Revised basicGetto simply call TypeUtil.getFeatureMembershipOf.
• TypeUtil – Added getFeatureMembershipOf to provide access to TypeAdapter.getFeatureMembership.
• TypeAdapter – Implemented getFeatureMembership as discussed above. Implementing this in the adapter allows the computed featureMembership to be cached (alongside inheritedMembership).

[himi]

It tool much time to understand what the critical issue, but now I think I can understand. We need to properly filter featureMembership to keep type compatibility. And I did not notice import memberships are inherited! So I tested it with:

package Test {
    part def A {
        part f;
    }
    part def Bprivate {
        private import A::*;
        part g;
    }
    part def Bpublic {
        public import A::*;
        part g;
    }
    part def Bprotected {
        protected import A::*;
        part g;
    }
    part def Cprivate :> Bprivate;
    part def Cpublic :> Bpublic;
    part def Cprotected :> Bprotected;
}

And get owningType of thier featureMembership with the following code:

from mgpy.mg import iMg
def showFeatureMembership(q):
    C = iMg.dq(q)[0]
    print(f'{C.qualifiedName}')
    for ms in C.featureMembership:
        e = ms.memberElement
        if not e.isStandardLibrary:
            print(f'  {e.qualifiedName} owningType: {ms.owningType.qualifiedName}')

showFeatureMembership('Test.A')
showFeatureMembership('Test.Bpublic')
showFeatureMembership('Test.Bprivate')
showFeatureMembership('Test.Bprotected')
showFeatureMembership('Test.Cprivate')
showFeatureMembership('Test.Cpublic')
showFeatureMembership('Test.Cprotected')

And then I obtained:

Test::A
  Test::A::f owningType: Test::A
Test::Bpublic
  Test::Bpublic::g owningType: Test::Bpublic
Test::Bprivate
  Test::Bprivate::g owningType: Test::Bprivate
Test::Bprotected
  Test::Bprotected::g owningType: Test::Bprotected
Test::Cprivate
  Test::Bprivate::g owningType: Test::Bprivate
Test::Cpublic
  Test::Bpublic::g owningType: Test::Bpublic
Test::Cprotected
  Test::Bprotected::g owningType: Test::Bprotected

They are correct!

[himi]

Just FYI, before this fix, I got:

Test::A
  Test::A::f owningType: Test::A
Test::Bpublic
  Test::Bpublic::g owningType: Test::Bpublic
Test::Bprivate
  Test::Bprivate::g owningType: Test::Bprivate
Test::Bprotected
  Test::Bprotected::g owningType: Test::Bprotected
Test::Cprivate
  Test::Bprivate::g owningType: Test::Bprivate
Test::Cpublic
  Test::Bpublic::g owningType: Test::Bpublic
  Test::A::f owningType: Test::A
Test::Cprotected
  Test::Bprotected::g owningType: Test::Bprotected
  Test::A::f owningType: Test::A