Investigate if Extensible Enums Members Can Be Restored via Back Compat

[jorgerangel-msft]

There's at least one scenario in the mgmt libraries where an extensible enum removed members between versions which would be a breaking change.

• Azure.ResourceManager.CostManagement

We should investigate if this is feasable to support via back compat. There may be some limitations in the current implementation, since we don't pull the symbols when loading a library's last contract dll

[github-actions]

🎯 Issue Triage

This is an investigation task to determine whether the C# client emitter can support back-compat restoration of extensible enum members that were removed between API versions, using the Azure.ResourceManager.CostManagement library as a concrete example.

Category: Feature Request

Area: emitter:client:csharp

🔍 Analysis

• The issue identifies a real-world case in Azure.ResourceManager.CostManagement where an extensible enum (OperationStatusType) had members removed in a newer version — which constitutes a breaking change for SDK consumers.
• The request is to investigate whether the back-compat mechanism in the C# emitter (which already handles underscore naming preservation) could be extended to also restore removed enum members.
• A known limitation mentioned: the emitter currently does not load DLL symbols from a library's last contract, which may constrain what's detectable for back-compat purposes.
• Related issues: Add back compat for extensible enum members that used underscores #10537 (back compat for underscore enum members), Check Custom Code When Preserve enum member underscores for backcompat #11314 (check custom code when preserving enum member underscores — closed/completed).

📝 Suggested next steps

• Investigate how the current back-compat mechanism loads the previous contract and what data is available (symbols, DLL, etc.)
• Determine if removed enum members can be detected from the last contract without DLL symbol loading
• Prototype restoring removed extensible enum members and validate against OperationStatusType in Azure.ResourceManager.CostManagement
• Assess if restored members conflict with custom code (similar to the check done in Check Custom Code When Preserve enum member underscores for backcompat #11314)

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