test: Ensure back-compat of new _code fields in TOML archives

[kdmccormick]

[Do Not Merge]

This is a test PR to see how changes to the backup-restore format in #544 and #545 would work on Ulmo instance.

This PR is based on v0.30.2, which is what release/ulmo pins.

Context: #544 (comment)

[kdmccormick]

@ormsbee @bradenmacdonald Could I get your take on which of these formats to use for Verawood? I'm leaning 2 or 3.

All of these could be implemented to be backwards-compatible with Ulmo instances. Existing Ulmo-generated archives would be forwards compatible with Verawood instances, as the Verawood instance would just fall back to parsing [entity].key

Option 1

This is what I have implemented now.

[entity.component]
component_type = "xblock.v1:html"
component_code = "c22b9f97-f1e9-4e8f-87f0-d5a3c26083e2"

Option 2

This would match how an [entity.container] is defined. You could imagine additional component-type-specific data going into this table.

[entity.component."xblock.v1".html]
component_code = "c22b9f97-f1e9-4e8f-87f0-d5a3c26083e2"

Option 3

No changes for Verawood. Just continue parsing[entity].key. A future v2 format would implement something like the options above, and it would replace [entity].key with [entity].entity_ref.

[kdmccormick]

For containers, I have similar question. Option 1 doesn't make sense given the existence of [entity.container.<subclass>] in the format. So, it's either:

Option 2

[entity.container.subsection]
container_code = "unit-foo-bar-baz"

Option 3

No changes. Just continue using [entity].key as the container_code.

[ormsbee]

I think (1) or (3). The container_code and container_type are things handled by the container applet, and are not specific to a kind of container. Likewise with component.

[kdmccormick]

Option (1) is unfortunately impossible for containers without breaking Ulmo backcompat, due to how strict this existing validation code is:

openedx-core/src/openedx_content/applets/backup_restore/serializers.py

Lines 131 to 135 in cbc344b

	if not isinstance(value, dict) or len(value) != 1:
	errors.append("Container must be a dict with exactly one key.")
	if len(value) == 1: # Only check the key if there is exactly one
	container_type = list(value.keys())[0]
	if container_type not in ("section", "subsection", "unit"):

That is, the following TOML

[entity.container]
container_code = "blah"

[entity.container.subsection]
...

will yield "Container must be a dict with exactly one key.".

Given that, I think we should keep things simple and just wait until "v2" before making any backup-restore format changes.

As an aside @ormsbee @bradenmacdonald , if/when we do TOML v2, I think we should aim to make Restore fairly permissive as to allow future backwards-compatible additions to the format.