fix(http-server-csharp): align error constructor types

[sophia-ramsey]

This pull request addresses the way error model constructors are generated in the C# server emitter, ensuring that the constructor parameters use the correct generated property types for all supported shapes (records, arrays, tuples, and nullable unions). It also improves detection of when error models require JsonObject/JsonNodes imports and removes legacy type string generation logic. Comprehensive tests are added to verify the new behavior.

Error model constructor improvements

• Error model constructors now use generated property types for parameters, including support for records, arrays, tuples, and nullable unions, ensuring accurate C# type mapping. [1] [2]

Improved detection for JsonObject usage

• Enhanced the modelNeedsJsonNodes function to recursively detect when a model or any of its inherited properties require JsonObject (for nested or inherited record types), and updated its usage to include inherited properties for root error models. [1] [2]

Code cleanup and refactoring

• Removed the legacy getCSharpTypeString function in favor of using the TypeExpression component for type rendering, simplifying type handling logic. [1] [2]

Testing

• Added comprehensive tests to verify that error model constructors are generated with the correct parameter types and that necessary using statements for JsonObject are included when required by inherited properties.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-server-csharp@11902

commit: dbe8609

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

Show changes

@typespec/http-server-csharp - fix ✏️

Use generated property types for error model constructor parameters, including records, arrays, tuples, and nullable unions.

[azure-sdk-automation]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[Copilot]

🟢 Approval recommended

The changes are scoped, consistent with existing emitter/type-rendering behavior, and include targeted tests plus a valid .chronus fix entry.

Pull request overview

This PR fixes C# http-server emitter error model constructor generation so constructor parameters use the same rendered C# types as the emitted model properties (covering records, arrays, tuples, and nullable unions), and updates JsonNodes import detection to include inherited properties for root error models.

Changes:

• Switched error constructor parameter type rendering from legacy string mapping to the shared TypeExpression renderer.
• Enhanced modelNeedsJsonNodes to recursively detect JsonObject usage through nested types and (optionally) inherited properties, and wired it for root error models.
• Added tests validating constructor parameter types and System.Text.Json.Nodes import emission for inherited record properties.

File summaries

File	Description
packages/http-server-csharp/src/components/models/models.tsx	Passes a “root error model” flag to include inherited properties when deciding whether System.Text.Json.Nodes is needed.
packages/http-server-csharp/src/components/models/model-helpers.ts	Refactors modelNeedsJsonNodes into a recursive type-walk with optional base-model traversal; removes legacy getCSharpTypeString.
packages/http-server-csharp/src/components/models/error-models.tsx	Uses TypeExpression for error constructor parameter types to align with generated property types.
packages/http-server-csharp/src/components/models/error-models.test.tsx	Adds coverage for structured constructor parameter typing and inherited JsonObject import detection.
.chronus/changes/fix-csharp-error-constructor-types-2026-9-8.md	Adds a fix changeset for @typespec/http-server-csharp describing the user-visible behavior change.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 0
• Review effort level: Lite

---

💡 Configure MCP servers for context-aware, tailored reviews. Learn more in the docs.