[http-server-csharp] add arrayDeclarationContext

.chronus/changes/sramsey-csharp-service-arrayDeclarationContext-2026-3-9-13-37-52.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-server-csharp"
+---
+
+add arrayDeclarationContext 

packages/http-server-csharp/src/lib/service.ts

@@ -214,6 +214,14 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
       return "TypeSpec.Service";
     }
 
+    arrayDeclarationContext(array: Model, name: string, elementType: Type) {
+      const arrayName = ensureCSharpIdentifier(this.emitter.getProgram(), array, name);
+      const arrayFile = this.emitter.createSourceFile(`generated/models/${arrayName}.cs`);
+      arrayFile.meta[this.#sourceTypeKey] = CSharpSourceType.Model;
+      const arrayNamespace = this.#getOrAddNamespace(array.namespace);
+      return this.#createModelContext(arrayNamespace, arrayFile, arrayName);
+    }
+
     arrayDeclaration(array: Model, name: string, elementType: Type): EmitterOutput<string> {
       return this.collectionDeclaration(elementType, array);
     }

packages/http-server-csharp/test/generation.test.ts

@@ -3396,6 +3396,109 @@ describe("collection type: defined as emitter option", () => {
   });
 });
 
+describe("arrayDeclarationContext", () => {
+  it("generates a dedicated file for array model declarations", async () => {
+    await compileAndValidateMultiple(
+      tester,
+      `
+        model Tags is Array<string>;
+        @route("/tags") @get op getTags(): Tags;
+        `,
+      [
+        [
+          "Tags.cs",
+          [
+            "// Generated by @typespec/http-server-csharp",
+            "using System;",
+            "using System.Text.Json;",
+            "using System.Text.Json.Serialization;",
+            "using TypeSpec.Helpers.JsonConverters;",
+            "using TypeSpec.Helpers;",
+          ],
+        ],
+        ["IContosoOperations.cs", ["Task<string[]> GetTagsAsync( )"]],
+      ],
+    );
+  });
+
+  it("generates a dedicated file for array model with custom namespace", async () => {
+    await compileAndValidateMultiple(
+      tester,
+      [
+        `
+        model Items is Array<int32>;
+        @route("/items") @get op getItems(): Items;
+        `,
+        "My.Custom.Ns",
+      ],
+      [
+        ["Items.cs", ["// Generated by @typespec/http-server-csharp", "using System;"]],
+        ["INsOperations.cs", ["Task<int[]> GetItemsAsync( )"]],
+      ],
+    );
+  });
+
+  it("generates a dedicated file for array model with complex element type", async () => {
+    await compileAndValidateMultiple(
+      tester,
+      `
+        model Widget {
+          id: int32;
+          name: string;
+        }
+        model WidgetList is Array<Widget>;
+        @route("/widgets") @get op getWidgets(): WidgetList;
+        `,
+      [
+        [
+          "Widget.cs",
+          [
+            "public partial class Widget",
+            "public int Id { get; set; }",
+            "public string Name { get; set; }",
+          ],
+        ],
+        ["WidgetList.cs", ["// Generated by @typespec/http-server-csharp", "using System;"]],
+        ["IContosoOperations.cs", ["Task<Widget[]> GetWidgetsAsync( )"]],
+      ],
+    );
+  });
+
+  it("generates a dedicated file for named array with union element type", async () => {
+    await compileAndValidateMultiple(
+      tester,
+      `
+        model ToolCall {
+          id: string;
+          type: "function";
+          name: string;
+        }
+
+        model CustomToolCall {
+          id: string;
+          type: "custom";
+          payload: string;
+        }
+
+        /** The tool calls generated by the model, such as function calls. */
+        model ToolCalls is (ToolCall | CustomToolCall)[];
+
+        model AssistantMessage {
+          role: "assistant";
+          tool_calls?: ToolCalls;
+        }
+
+        @route("/chat") op chat(): AssistantMessage;
+        `,
+      [
+        ["AssistantMessage.cs", [`public string Role { get; } = "assistant";`]],
+        ["ToolCalls.cs", ["// Generated by @typespec/http-server-csharp"]],
+        ["IContosoOperations.cs", ["Task<AssistantMessage> ChatAsync( );"]],
+      ],
+    );
+  });
+});
+
 it("emits class for model extending another model with no additional properties", async () => {
   await compileAndValidateMultiple(
     tester,