[C#] Emit Obsolete attributes for deprecated model properties by Copilot · Pull Request #12523 · microsoft/typespec

Copilot · 2026-11-09T23:57:30Z

Property-level #deprecated messages were dropped during generation, leaving consumers without compiler warnings.

Metadata: Carry the exact message from TypeSpec through the serialized model to property generation.
Emission: Generate [Obsolete(message)] on ordinary and renamed/customized models, reusing existing warning suppressions for generated references.
Customization: Preserve handwritten attributes without duplicates; leave non-deprecated properties unchanged.

For #deprecated "Use replacement instead.", emit:

[Obsolete("Use replacement instead.")]
public string Legacy { get; set; }

Fixes [C# generator] Emit [Obsolete] attribute for properties marked with #deprecated #12522

azure-pipelines · 2026-11-09T23:57:53Z

Azure Pipelines: Successfully started running 1 pipeline(s). 1 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

Co-authored-by: JoshLove-msft <54595583+JoshLove-msft@users.noreply.github.com>

Copilot

🟡 Changes recommended

Deprecation handling leaves unsuppressed warnings in generated inheritance and property-access paths that break warnings-as-errors builds, and lacks compatibility guards for previously published properties.

3 open issues

What changed in this PR

This PR addresses #12522 by carrying property deprecation metadata through the C# emitter and generating [Obsolete(message)] attributes so SDK consumers receive compiler warnings.

Changes:

Preserve exact deprecation messages through serialization and property generation.
Cover ordinary and renamed models, handwritten attributes, and non-deprecated properties.
Update generated samples and suppress intentional deprecated-property references in tests.

File	Description
`packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/tspCodeModel.json`	Records property deprecation messages.
`packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/RenamedModelCustom.Serialization.cs`	Suppresses warnings around deprecated-property serialization.
`packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/RenamedModelCustom.cs`	Adds the attribute and constructor warning suppressions.
`packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/CurrentDetails.cs`	Emits an attribute with an escaped message.
`packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/Sample-TypeSpec.tsp`	Adds deprecated-property sample declarations.
`packages/http-client-csharp/generator/TestProjects/Local.Tests/CustomizationTests.cs`	Checks emitted messages and unaffected properties.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/TypeProviderTests.cs`	Tests metadata, attributes, and customization handling.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/TestData/TypeProviderTests/DeprecatedPropertiesPreserveMessagesAndCustomizations/Custom.cs`	Supplies a renamed model with a handwritten attribute.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Providers/PropertyProvider.cs`	Adds deprecation attributes to generated properties.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/Serialization/InputModelPropertyConverter.cs`	Deserializes property deprecation messages.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/InputModelProperty.cs`	Stores property deprecation metadata.
`packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/ModelReaderWriterValidation/TestProjects/Sample_TypeSpec/RenamedModelTests.cs`	Suppresses intentional deprecated-property usage in tests.
`packages/http-client-csharp/emitter/test/Unit/model-type.test.ts`	Tests absent, empty, and escaped deprecation messages.
`packages/http-client-csharp/emitter/src/type/input-type.ts`	Extends the property metadata interface.
`packages/http-client-csharp/emitter/src/lib/type-converter.ts`	Reads property deprecation from TypeSpec.

_{Review effort: Balanced}

pkg-pr-new · 2026-11-10T15:52:27Z

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-csharp@12523

commit: 2a1a28f

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-11-10T21:06:56Z

No changes needing a change description found.

Copilot

🟡 Changes recommended

Unsuppressed deprecation warnings in generated property forwarding, exploded queries, and paging helpers break warnings-as-errors builds, while lazy attribute filtering can discard unrelated attributes.

4 open issues

3 resolved since last review

_{Review effort: Balanced}

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

🔵 Needs a closer look

Human review is needed because inherited-only overrides may lose base-property metadata, leaving obsolete-member warnings unsuppressed in paging access.

No open issues 🎉

1 resolved since last review

Preserve base diagnostic IDs when removing generated attributes

_{Review effort: Balanced}

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

🔵 Needs a closer look

Human assessment is needed because public API signature changes break source and binary compatibility for supported generator extensions, including runtime failures in previously compiled plugins.

No open issues 🎉

_{Review effort: Balanced}

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

🔵 Needs a closer look

Human assessment is needed because replacing a public overload breaks compatibility with existing generator extensions, a critical concern omitted from the published review.

No open issues 🎉

_{Review effort: Balanced}

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

JoshLove-msft · 2026-11-11T22:13:30Z

Re: the review summary's note about a replaced public overload. Fixed in c8b9fc1. I restored the public ModelProviderSnippets.GetPropertyExpression(ModelProvider, ValueExpression, IReadOnlyList<string>, out PropertyProvider) overload that this PR had replaced. The new overload, which also returns the properties accessed along the path, is added alongside it. Existing generator extensions that call the original overload keep compiling and binding. I checked the diff against main, and no other public or protected members are removed.

--generated by Copilot

JoshLove-msft · 2026-11-11T22:20:00Z

Re: the review summary's note about a replaced public overload. Fixed in c8b9fc1. I restored the public ModelProviderSnippets.GetPropertyExpression(ModelProvider, ValueExpression, IReadOnlyList<string>, out PropertyProvider) overload that this PR had replaced. The new overload, which also returns the properties accessed along the path, is added alongside it. Existing generator extensions that call the original overload keep compiling and binding. I checked the diff against main, and no other public or protected members are removed.

--generated by Copilot

We don't need to retain the public overload for backwards compatibililty. Revert this commit.

Copilot

🔵 Needs a closer look

Human assessment is needed because the compatibility check can miss inherited public properties and introduce new consumer warnings when they are redeclared as deprecated.

No open issues 🎉

_{Review effort: Balanced}

This reverts commit c8b9fc1. The original public overload does not need to be kept for backward compatibility. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

JoshLove-msft · 2026-11-11T22:48:47Z

Reverted in f698371, so the restored GetPropertyExpression overload is gone.

Also fixed the issue in the latest review summary in 2a1a28f. The last-contract check only looked at properties declared directly on the model's last-contract type. Suppose a property was inherited from a base class in the last contract, such as InheritingModel.PreviouslyStable coming from StableModel, and is now redeclared on the derived model as deprecated. The check found no previous declaration and added [Obsolete], giving consumers who already used that stable property new warnings. The check now walks the last-contract base types and uses the nearest public declaration. PropertyDeprecationPreservesInheritedLastContract covers stable, obsolete, and new inherited cases, and the stable case fails without the fix.

--generated by Copilot

Copilot

🟡 Changes recommended

Replacing the public four-parameter GetPropertyExpression overload breaks existing source callers and compiled generator plugins; it should remain as a forwarding wrapper alongside the new overload.

1 open issue

Preserve the existing four-parameter public overload · New

_{Review effort: Balanced}

Initial plan

98b4365

Copilot AI assigned Copilot and JoshLove-msft Nov 9, 2026

Copilot started work on behalf of JoshLove-msft November 9, 2026 23:58

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Copilot AI linked an issue Nov 9, 2026 that may be closed by this pull request

[C# generator] Emit [Obsolete] attribute for properties marked with #deprecated #12522

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3 tasks done

fix(csharp): emit Obsolete attributes for deprecated model properties

cb187aa

Co-authored-by: JoshLove-msft <54595583+JoshLove-msft@users.noreply.github.com>

microsoft-github-policy-service Bot added the emitter:client:csharp Issue for the C# client emitter: @typespec/http-client-csharp label Nov 10, 2026

Copilot AI changed the title ~~[WIP] Emit [Obsolete] attribute for properties marked with #deprecated~~ [C#] Emit Obsolete attributes for deprecated model properties Nov 10, 2026

Copilot finished work on behalf of JoshLove-msft November 10, 2026 00:19

Copilot AI requested a review from JoshLove-msft November 10, 2026 00:19

JoshLove-msft marked this pull request as ready for review November 10, 2026 01:18

JoshLove-msft requested review from Alan Zimmer (alzimmermsft), Jorge Rangel (jorgerangel-msft), Jose Arriaga Maldonado (joseharriaga) and m-nash as code owners November 10, 2026 01:18

Copilot AI balanced review requested due to automatic review settings November 10, 2026 01:18

Copilot started reviewing on behalf of JoshLove-msft November 10, 2026 01:22

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Alan Zimmer (alzimmermsft) reviewed Nov 10, 2026

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Comment thread ...t-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/CurrentDetails.cs Resolved

Alan Zimmer (alzimmermsft) approved these changes Nov 10, 2026

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fix(csharp): handle obsolete properties in generated clients

e22ffe4

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 10, 2026 21:02

Copilot started reviewing on behalf of JoshLove-msft November 10, 2026 21:03

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fix(csharp): handle inherited obsolete property references

13b61ea

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 10, 2026 22:27

Copilot started reviewing on behalf of JoshLove-msft November 10, 2026 22:28

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Jorge Rangel (jorgerangel-msft) reviewed Nov 11, 2026

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Comment thread .../http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Providers/PropertyProvider.cs Resolved

fix(csharp): suppress deprecated members in multipart file overloads

fc61c66

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 11, 2026 20:49

Jorge Rangel (jorgerangel-msft) reviewed Nov 11, 2026

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Copilot started reviewing on behalf of JoshLove-msft November 11, 2026 20:57

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refactor(csharp): reuse base model chain and virtual deprecation hook

2f8e966

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 11, 2026 21:33

Copilot started reviewing on behalf of JoshLove-msft November 11, 2026 21:34

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JoshLove-msft enabled auto-merge November 11, 2026 21:36

Jorge Rangel (jorgerangel-msft) approved these changes Nov 11, 2026

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Copilot AI reviewed Nov 11, 2026

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fix(csharp): restore public GetPropertyExpression overload

c8b9fc1

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 11, 2026 22:13

Copilot started reviewing on behalf of JoshLove-msft November 11, 2026 22:14

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JoshLove-msft and others added 2 commits November 11, 2026 14:44

revert(csharp): drop restored GetPropertyExpression overload

f698371

This reverts commit c8b9fc1. The original public overload does not need to be kept for backward compatibility. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

fix(csharp): check inherited last-contract properties for deprecation

2a1a28f

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI balanced review requested due to automatic review settings November 11, 2026 22:48

Copilot started reviewing on behalf of JoshLove-msft November 11, 2026 22:50

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Jorge Rangel (jorgerangel-msft) approved these changes Nov 11, 2026

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Copilot AI reviewed Nov 11, 2026

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Comment thread ...p-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Snippets/ModelProviderSnippets.cs Resolved

JoshLove-msft added this pull request to the merge queue Nov 11, 2026

Merged via the queue into main with commit ccde4f5 Nov 12, 2026
31 checks passed

JoshLove-msft deleted the copilot/emit-obsolete-attribute branch November 12, 2026 00:48

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