Use enum instead of bool for USD contribution variant

[tadeas-hejnic]

Changelog Description

This PR is adding an option to Set as default variant selection during the publishing. Before there was only toggle that has this behaviour:
- True : Always set the variant as default
- False : Set as the default only if there is no default

So it wasn't possible to Don't set the variant as default if the default is not set yet. The current implementation is adding this option and maps also the previous values to the new enum.

Additional info

The conversion is done this way to keep the behaviour of the previous implementation the same:

1. False -> Set as default if no current default
2. True -> Set as default

The new option is Do not set, which really doesn't set the default even if there is no default yet.

Testing notes:

1. test publish with all possible choices in Set as default variant selection and check if it matches the settings
2. test conversion from older settings:
   • False -> Set as default if no current default
   • True -> Set as default

[tadeas-hejnic]

My test workflow

Tested all combinations of the new default variant selection policy, both with and without an existing variant selection.

• never with no existing selection

  • Published a new variant to a clean target.
  • Verified that the variant was added.
  • Verified that no variant selection was authored.

• if_not_set with no existing selection

  • Published a new variant to a clean target.
  • Verified that the variant was added.
  • Verified that it became the selected/default variant.

• always with no existing selection

  • Published a new variant to a clean target.
  • Verified that the variant was added.
  • Verified that it became the selected/default variant.

• never with an existing selection

  • Published an additional variant to a target that already had Base selected.
  • Verified that the new variant was added.
  • Verified that the existing Base selection was preserved.

• if_not_set with an existing selection

  • Published an additional variant to the same target.
  • Verified that the new variant was added.
  • Verified that the existing Base selection was preserved.

• always with an existing selection

  • Published an additional variant to the same target.
  • Verified that the new variant was added.
  • Verified that the existing selection was overridden and changed to the newly published variant.

All six policy scenarios behaved as expected.

[BigRoy]

Cool, very solid!

Should we rename key if_missing to if_not_set?

@MustafaJafar can you give it a spin?

[Copilot]

Pull request overview

This PR replaces the USD contribution “set variant as default” boolean with an enum-style policy to support a third option (“do not set”), while preserving legacy behavior through settings conversion and backward-compatible fallbacks in the publisher.

Changes:

• Introduces contribution_variant_default_policy with three modes: if_missing, always, never (server settings + client publish attributes).
• Adds a server-side settings conversion to map legacy contribution_variant_is_default booleans to the new enum values.
• Updates USD layer contribution extraction to author default variant selection based on the selected policy.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
server/settings/publish_plugins.py	Adds the enum-based setting and updates default publish profiles to use it.
server/settings/conversion.py	Adds a conversion step to migrate legacy boolean settings to the new enum field.
client/ayon_core/plugins/publish/extract_usd_layer_contributions.py	Updates publish attribute UI + extraction logic to use the new policy and keep backward compatibility.

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[tadeas-hejnic]

Tested after the changes suggested by @iLLiCiTiT and everything works.

[BigRoy]

LGTM - just some cosmetic notes only left.