Remove Old Enclave Code

[rasswanth-s]

Description

To be added

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List any dependencies that are required for this change.

How has this been tested?

Existing tests

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• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests

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[BrendanSchell]

Just for my understanding, is there a reason we keep old versions around? I'm more used to alembic kind of model where you specify the diffs for migrations and doing it this way looks like you have to keep around some constructs like EnclaveMetadata that aren't being used anywhere after the rest of this code gets deleted.

[rasswanth-s]

We keep the old versions mainly for the upgradeability.
You are correct, when we delete specific attributes in a object which in itself is a python class and if do not we use the object elsewhere, we would have to keep it around for upgradeability.

In our case , we deleted enclave_metadata field in the new version of UserCode
Since enclave_metadata is a python Class: EnclaveMetadata, I think we still need to keep the class for upgradeability even if it not being used elsewhere.

cc: @shubham3121 @koenvanderveen is there a better way to solve this?

[shubham3121]

So currently we keep the last version of the class along with the latest version of the class. The thing we're missing for UserCodeV5 is the function that allows to migrate up/down. e.g. we have functions migrate_usercode_v4_to_v5 and migrate_usercode_v5_to_v4 that do that for user code v4->v5 and vice-versa. We need to update these for usercode v5 <-> v6. For ease of simplicity we can rename these functions to:

@migrate(UserCodeV4, UserCode)          @migrate(UserCodeV5, UserCode)
def migrate_usercode_v4_to_v5       ---->  def upgrade_usercode

and

@migrate(UserCodeV4, UserCode)            @migrate(UserCodeV5, UserCode)
def migrate_usercode_v5_to_v4         ->     def downgrade_usercode

and then define the respective defaults to convert one object version to another.