fix(http-server-csharp): emitter type errors

[sophia-ramsey]

Addresses errors I encountered while using the C# server emitter to emit code from the ai foundry spec for the agent contracts api service package. Includes tests

Issues addressed:

• duplicate nullable suffixes: fixed optional nullable value parameters emitting invalid C# types by ensuring nullable suffixes are applied only once (int?? to int?)
• multipart content: fixed multipart operations emitting <Unresolved Symbol ...> by falling back to the original @multipartBody metadata when canonicalization data is unavailable
• record parameter fixes: fixed error-model constructors emitting incompatible types such as Record, Array, or object instead of the same concrete structured types used by their properties
• parameter ordering fix: fixed controller calls passing positional arguments in a different order than their business-interface signatures while preserving positional syntax for existing generated code
• void as a success type: fixed void | @error responses generating invalid result assignments by excluding error branches from success-response analysis and emitting direct awaits with NoContent()
• optional nullables for errors: errors with optional properties would emit with those properties non-optional and only show as optional if the spec specified | null
• fix model only emitter option: output-type:models was emitting controllers and responses, and it now emits models only
• namespace issue: the emitter was generating code with the wrong namespace, using whichever namespace was the first to appear in the typespec (ex. using the namespace of a package that was imported) instead of the intended namespace

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

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@typespec/http-server-csharp - fix ✏️

fix optional error properties, output-type:models, and incorrect namespace issue

@typespec/http-server-csharp - fix ✏️

fix errors in emitter including duplicate nullable suffixes, unresolved symbols for multipart content, incompatible types, parameter ordering, and void as a success type

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npm i https://pkg.pr.new/@typespec/http-server-csharp@11749

commit: cde3acf

[Copilot]

Pull request overview

This PR fixes several correctness issues in the @typespec/http-server-csharp emitter that surfaced when generating controllers/models from a larger real-world spec (nullable handling, multipart fallback behavior, error model ctor typing, operation canonicalization/service namespace resolution, controller call argument ordering, and models-only output). It also updates snapshots and adds targeted tests to prevent regressions.

Changes:

• Fixes nullable emission across models, interfaces, mocks, controllers, and error constructors (including avoiding invalid T??).
• Improves service discovery/namespace selection and introduces an operation-source map to better align controller generation with business/interface operations.
• Adds/updates tests and snapshots for models-only output, multipart fallback behavior, and controller/action response analysis.

Reviewed changes

Copilot reviewed 25 out of 28 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/http-server-csharp/test/snapshots/sample-service/generated/models/PetListResult.cs	Snapshot update: nullable reference type for optional nextLink.
packages/http-server-csharp/test/snapshots/sample-service/generated/models/Pet.cs	Snapshot update: nullable reference types for optional properties.
packages/http-server-csharp/test/snapshots/sample-service/generated/controllers/PetsController.cs	Snapshot update: DELETE returns 204 NoContent without assigning void result.
packages/http-server-csharp/test/nullable-parameters.test.ts	New regression test ensuring optional nullable value params don’t emit T??.
packages/http-server-csharp/test/generation.test.ts	Updates expectations for nullable reference types and error ctor optional nullables.
packages/http-server-csharp/test/emitter.test.ts	Adds test verifying output-type=models emits only models/support files.
packages/http-server-csharp/src/utils/namespace-utils.ts	Removes findServiceNamespace (service resolution moved to service-discovery).
packages/http-server-csharp/src/service-resolution.ts	Adds options to skip canonicalization; tracks canonical op → source operation map; uses declared service namespace.
packages/http-server-csharp/src/service-resolution.test.ts	Adds tests for declared service namespace precedence, operation source tracking, and canonicalization skipping.
packages/http-server-csharp/src/service-discovery.ts	Introduces getServiceNamespace and uses compiler helper for full namespace name.
packages/http-server-csharp/src/emitter.tsx	Implements models-only emission path; wires operation source context; avoids emitting mocks/project/docs in models-only mode.
packages/http-server-csharp/src/context/operation-source-context.ts	New context for canonical operation → source operation mapping.
packages/http-server-csharp/src/components/type-expression/type-expression.tsx	Adds helper for detecting nullable value-type unions; uses it in union type rendering.
packages/http-server-csharp/src/components/scaffolding/mock-implementations.tsx	Multipart fallback without canonical metadata; fixes nullable value union parameter emission in mocks.
packages/http-server-csharp/src/components/render-root.tsx	Detects multipart based on decorators when canonicalization is unavailable.
packages/http-server-csharp/src/components/multipart-fallback.test.tsx	New test ensuring multipart interfaces/mocks stay aligned without canonical metadata.
packages/http-server-csharp/src/components/models/models.tsx	Adjusts nullable semantics for properties; improves JsonNodes detection for inherited error models.
packages/http-server-csharp/src/components/models/model-helpers.ts	Enhances JsonNodes detection to recurse into tuples/arrays/records and optionally include inheritance.
packages/http-server-csharp/src/components/models/error-models.tsx	Uses TypeExpression for structured ctor param types; fixes optional/nullability behavior in error ctors.
packages/http-server-csharp/src/components/models/error-models.test.tsx	New tests for structured ctor parameter typing and inherited JsonObject using.
packages/http-server-csharp/src/components/interfaces/interfaces.tsx	Multipart fallback via decorators; fixes optional nullable value union parameters (avoids T??).
packages/http-server-csharp/src/components/interfaces/interfaces.test.tsx	New tests for nullable suffix correctness and multipart fallback behavior.
packages/http-server-csharp/src/components/controllers/controllers.tsx	Passes operation source into ControllerAction to improve call-site alignment.
packages/http-server-csharp/src/components/controllers/controllers.test.tsx	Adds controller ordering test using operation source context.
packages/http-server-csharp/src/components/controller-action/response-analysis.ts	Excludes error branches from success-response analysis; returns 204 when success is void.
packages/http-server-csharp/src/components/controller-action/controller-action.tsx	Reorders call args to match business/interface signature; updates ProducesResponseType/body handling for void unions.
packages/http-server-csharp/src/components/controller-action/controller-action.test.tsx	Adds tests for void-success unions, preserving value-success behavior, and argument ordering for request/protocol params.
.chronus/changes/sramsey-csharp-server-nullable-2026-7-12-14-45-16.md	Changelog entry for the emitter fixes.

Suppressed comments (3)

packages/http-server-csharp/src/components/controller-action/controller-action.tsx:61

• Controller action parameters can still emit int?? for value?: int32 | null because TypeExpression returns int? and optional: true adds another ?. Passing the inner value type to TypeExpression (only when the parameter is optional and the union is a nullable value union) avoids the duplicate suffix.

        type: <TypeExpression type={p.property.sourceType.type} />,

packages/http-server-csharp/src/components/controller-action/controller-action.tsx:72

• Same T?? risk exists for optional nullable value unions on query/header parameters; TypeExpression emits T? for T | null and the optional flag adds another ?. Apply the same inner-type substitution here to keep controller method signatures valid.

        type: <TypeExpression type={p.property.sourceType.type} />,

packages/http-server-csharp/src/components/controllers/controllers.test.tsx:142

• The expected controller implementation calls GetPetAsync(feature, petId, apiVersion), but the expected interface signature just above is GetPetAsync(string petId, string feature, string apiVersion). This would not compile as generated code; the argument order in the expected output should match the interface signature.

            var result = await PetStoreImpl.GetPetAsync(feature, petId, apiVersion);

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[Copilot]

Pull request overview

Copilot reviewed 26 out of 29 changed files in this pull request and generated no new comments.

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

packages/http-server-csharp/src/components/controller-action/controller-action.tsx:173

• responseStatusCode for [ProducesResponseType] is currently derived only from hasBody, but the method body can return Accepted(...) when statusCode === 202 (and StatusCode(statusCode, ...) for other non-200 codes). This can cause the emitted attribute to advertise OK/NoContent even when the action returns 201/202, which makes the generated metadata inaccurate.

  // Determine the success status code from the response
  const { statusCode, hasBody } = getSuccessStatusCode($.program, props.operation);

  // Determine response type for ProducesResponseType attribute
  const returnType = props.operation.sourceType.returnType;
  const responseStatusCode = hasBody ? "OK" : "NoContent";
  let responseTypeExpr: Children | undefined = undefined;