Apply @@override options bags to protocol methods

[m-nash]

Fixes #11214

When @@override groups an operation's parameters into an options bag, only the convenience method adopted the grouped shape. The protocol method kept listing every parameter individually, so a spec that hides the convenience method (or a caller that wants the protocol surface) still got a 40-parameter signature.

Before / after

// Before
public virtual Response GetWidget(string id, string filter, int? top, RequestOptions options)

// After
public virtual Response GetWidget(GetWidgetOptions options, RequestOptions requestOptions)

Behavior

The protocol method must always retain a way to send a raw payload, so grouping is applied conditionally:

Options bag contains	Protocol method	Raw body preserved
no body parameter	(Options options, RequestOptions requestOptions)	n/a
body declared outside the bag	(BinaryContent content, Options options, RequestOptions requestOptions)	yes
body inside the bag	flattened, as today	yes

Implementation

RestClientProvider

• GetMethodParameters sources protocol parameters from serviceMethod.Parameters (the grouped shape) when grouping applies. CreateRequest continues to use the flattened operation.Parameters.
• Body conversion now also handles InputMethodParameter { Location: Body } so a body declared outside the bag still becomes request content.
• New ShouldGroupProtocolParameters decides applicability: at least one operation parameter carries MethodParameterSegments, and the segment root is not the request body.

ScmMethodProviderCollection

• BuildGroupedCreateRequestArguments expands each grouped parameter back out of the bag when calling CreateRequest, carrying over the enum-to-serialized-form conversion.
• ResolveRequestOptionsNameCollision renames the trailing request options parameter when the options bag is itself named options, which would otherwise emit a duplicate parameter name.

Tests

Three new tests cover the grouped shape, the body-outside-bag case, and the body-inside-bag fallback.

Two existing baselines changed: the convenience method now forwards the bag straight through instead of unpacking it. The client-name-mapping and enum-serialization logic those tests covered moved to the protocol-to-CreateRequest boundary, so I added assertions on the protocol body in the same tests rather than dropping that coverage.

Microsoft.TypeSpec.Generator.ClientModel 1543/1543 and Microsoft.TypeSpec.Generator 1810/1810 pass.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-csharp@11523

commit: 13bc727

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[Copilot]

Pull request overview

This PR updates the C# http-client generator so that when @@override groups operation parameters into an options bag, the protocol method can also adopt the grouped signature (while still preserving a raw request-body escape hatch when needed), addressing #11214.

Changes:

• Apply @@override options-bag grouping to protocol methods when safe (body not folded into the bag), keeping CreateRequest parameter flattening intact.
• Expand grouped parameters back into flattened wire parameters when calling CreateRequest, including enum-to-serialized conversions.
• Add/adjust tests and baselines to validate protocol/convenience behavior across grouped/no-body, body-outside-bag, and body-inside-bag scenarios.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/TestData/ScmMethodProviderCollectionTests/MethodParameterSegments_RenamedGroupedQueryParam_MapsByClientName.cs	Updates baseline to forward the options bag through the convenience method.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/TestData/ScmMethodProviderCollectionTests/MethodParameterSegments_EnumGroupedQueryParam_SerializesToProtocol.cs	Updates baseline to forward the options bag through the convenience method.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmMethodProviderCollectionTests.cs	Adds new test coverage for protocol-method options-bag grouping and body placement cases.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs	Implements protocol-to-CreateRequest argument expansion from grouped options bags and resolves request-options naming collisions.
packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/RestClientProvider.cs	Switches protocol method parameter sourcing to grouped parameters when applicable and improves body handling for grouped shapes.

[jorgerangel-msft]

triggered a regen preview https://dev.azure.com/azure-sdk/internal/_build/results?buildId=6653318&view=results