[release/10.0] Fix ObsoleteAttribute incorrectly causing XML serialization to ignore properties with AppContext switch and SR resources #119916
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Co-authored-by: StephenMolloy <[email protected]>
Co-authored-by: StephenMolloy <[email protected]>
Co-authored-by: StephenMolloy <[email protected]>
…ttribute behavior Co-authored-by: StephenMolloy <[email protected]>
…- which surface as errors in our build pipelines.
…izerTests.cs Co-authored-by: Copilot <[email protected]>
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Backport of #119865 to release/10.0
/cc @StephenMolloy @copilot
Customer Impact
XmlSerializer silently omits public members marked with [Obsolete], even though the attribute’s documented purpose is only to signal planned removal and guide developers at compile time. Because teams often stage deprecation by first adding [Obsolete] (with or without a warning-as-error) before later removing a member, this hidden coupling between deprecation metadata and runtime serialization creates a correctness and data loss risk: persisted XML stops containing the member’s data even though the member still exists and application code still reads it. This behavior is also inconsistent with the explicit opt out model already provided by [XmlIgnore].
Regression
Testing
Tests are added in this PR.
Risk
This is a low risk approach that prevents silent data omission while providing an escape hatch for existing applications. The risk of exceptions being thrown (for data that was being silently lost previously) is mitigated by an AppContext switch opt-out along with the increased awareness of the fact that XmlSerialzier was silently losing data before. :/
IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.