Emit experimental diagnostics in C# clients

[JoshLove-msft]

Summary

• preserve TypeSpec.HttpClient.@experimental diagnostic metadata in the C# input model
• emit [Experimental("C")] on generated protocol and convenience methods
• emit scoped warning suppressions for each dependsOn diagnostic in generated method and request bodies
• keep graduation explicit; the attribute remains until the decorator is removed

Companion to #11684, which adds diagnosticId and dependsOn to the shared decorator contract.

Validation

• C# emitter build
• focused emitter, input, and generator tests
• Cop static-analysis checks
• generated-library regeneration

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/http-client-csharp@11685

commit: 06639a1

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[JoshLove-msft]

Isn't this already handled by TCGC?

[JoshLove-msft]

TCGC does filter scope, but it currently checks only a top-level decoratorInfo.arguments["scope"]. @experimental receives ClientDecoratorOptions through its options parameter, so this value arrives as decoratorInfo.arguments.options.emitterScope and is not filtered by TCGC. I kept the local check, added a comment explaining the distinction, and retained coverage verifying metadata scoped to another emitter is ignored.

--generated by Copilot

[Copilot]

Pull request overview

This PR propagates TypeSpec.HttpClient.@experimental metadata through the C# emitter input model and uses it during C# client generation to (a) emit ExperimentalAttribute on generated API methods and (b) add scoped warning suppressions for diagnostics listed in dependsOn.

Changes:

• Extend the emitter/input-model contract to carry experimental: { diagnosticId, dependsOn } for operations, including JSON deserialization support and unit tests.
• Emit [Experimental("...")] on generated protocol and convenience methods when diagnosticId is present, and add #pragma warning disable/restore for each dependsOn diagnostic on generated methods (including request creation methods).
• Add emitter-side decorator extraction + tests to ensure @experimental metadata is captured with correct emitter scoping behavior.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/common/InputFactory.cs	Adds optional experimental details when creating InputOperation test inputs.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/test/TypeSpecInputConverterTests.cs	Adds a deserialization test validating experimental.diagnosticId and experimental.dependsOn.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/Serialization/InputOperationConverter.cs	Deserializes the new experimental payload into InputOperation.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/InputOperation.cs	Stores Experimental details on InputOperation and threads it through constructors.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.Input/src/InputTypes/InputExperimentalDetails.cs	Introduces a new input-model type to represent experimental diagnostic metadata.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmMethodProviderCollectionTests.cs	Validates attribute emission and dependency suppressions for experimental operations.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Utilities/ExperimentalApiHelpers.cs	Centralizes building experimental attributes and dependency suppressions.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs	Applies experimental attributes/suppressions to generated protocol and convenience methods.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/RestClientProvider.cs	Applies dependency suppressions to generated create-request methods.
packages/http-client-csharp/emitter/test/Unit/experimental-decorator.test.ts	Adds unit tests for extracting @experimental diagnostic metadata (including emitter scoping).
packages/http-client-csharp/emitter/src/type/input-operation.ts	Extends the TS input operation type to include experimental.
packages/http-client-csharp/emitter/src/options.ts	Ensures @experimental is captured via additionalDecorators.
packages/http-client-csharp/emitter/src/lib/operation-converter.ts	Populates operation.experimental from decorators during conversion.
packages/http-client-csharp/emitter/src/lib/decorators.ts	Adds getExperimentalDetails and emitter-scope filtering for @experimental metadata.

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