Resource equivalence contract broken in version v0.6.0

[Tomasz-Smelcerz-SAP]

What happened:
We use the OCM library for creating and distributing component archives in the Kyma-CLI project.
When upgrading the version from v0.4.0 to v0.6.0 I noticed that the pkg/contexts/ocm/compdesc.Resource.IsEquivalent() method is gone.
It looks like it's been replaced by a more sophisticated Equivalent(e ElementMetaAccessor) equivalent.EqualState method.
The new method has a different contract though, and I think there may be a bug there.
First, two identical Resource object copies (without optional Digest) are not considered "equivalent" anymore.
Second, two different Resource object (without optional Digest) are considered "localHashEqual".
None of the available checks work for me.

What you expected to happen:
Equality check allows to determine if two Resource objects without Digests are equal/equivalent.

How to reproduce it (as minimally and precisely as possible):
I have provided a little demo with unit tests:

• for version v0.4.0 - working OK
• for version v0.6.0 - doesn't work

Anything else we need to know:
We test resources for equality/equivalence to avoid unnecessary repository pushes (when the content doesn't change).

Environment:
n/a

[morri-son]

HI @mandelsoft , can you please have a look at this?

[mandelsoft]

The new equivalence behaviour has been introduced to better control transports and delta transports.
Together with this, now resources digests are generated directly together with the CV creation.
The digests are required to decide whether two resources are available because the access method may be
different. So, if no digests are found, it is not possible to decide,whether source and target of a transport are
identical. If digests are not present, IsArtifactDetectable() returns false.

May be this could be improved by involving the access method, if no digest is found.

But, the digests should now always be available, because they are always created when adding a resource
(if this in not explicitly disabled by an option)

[robertwol]

Hi @Tomasz-Smelcerz-SAP, does the above answer from @mandelsoft help?

[Tomasz-Smelcerz-SAP]

Hi, Thanks for reply.
Yes, that answers my question: I understand that digests are now expected to be present, so I have to adjust our code.
I was misled by this comment (in v0.6.0): https://github.com/open-component-model/ocm/blob/dfcf27e5f22d83feac7869e0f303c6e6e66f1e8d/pkg/contexts/ocm/compdesc/componentdescriptor.go#L671
Perhaps the comment could be improved somehow?

[morri-son]

@mandelsoft, can you please check Tomasz comment?

[mandelsoft]

Yes, the digest is optional. It is still possible to generate the digests on-the-fly, when they are required (during the signing process). But if the digests are not present, delta transports are not really possible, the overwrite is required.
By default, the composition calls in the CLI and the library now always calculate the digest (but you can specify options to skip this step).