Add @useSystemTextJsonConverter decorator for csharp

.chronus/changes/json-converter-2024-6-24-16-48-41.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Add `@hasJsonConverter` for csharp only to indicate if JSON converter is needed

docs/libraries/typespec-client-generator-core/reference/decorators.md

@@ -359,6 +359,33 @@ model Foo {
 model Bar {}
 ```
 
+### `@hasJsonConverter` {#@Azure.ClientGenerator.Core.hasJsonConverter}
+
+Whether a model needs the custom JSON converter, this is only used for backward compatibility for csharp.
+
+```typespec
+@Azure.ClientGenerator.Core.hasJsonConverter(scope?: valueof string)
+```
+
+#### Target
+
+`Model`
+
+#### Parameters
+
+| Name  | Type             | Description                                                                                                   |
+| ----- | ---------------- | ------------------------------------------------------------------------------------------------------------- |
+| scope | `valueof string` | The language scope you want this decorator to apply to. If not specified, will apply to all language emitters |
+
+#### Examples
+
+```typespec
+@hasJsonConverter
+model MyModel {
+  prop: string;
+}
+```
+
 ### `@include` {#@Azure.ClientGenerator.Core.include}
 
 :::warning

docs/libraries/typespec-client-generator-core/reference/index.mdx

@@ -46,6 +46,7 @@ npm install --save-peer @azure-tools/typespec-client-generator-core
 - [`@convenientAPI`](./decorators.md#@Azure.ClientGenerator.Core.convenientAPI)
 - [`@exclude`](./decorators.md#@Azure.ClientGenerator.Core.exclude)
 - [`@flattenProperty`](./decorators.md#@Azure.ClientGenerator.Core.flattenProperty)
+- [`@hasJsonConverter`](./decorators.md#@Azure.ClientGenerator.Core.hasJsonConverter)
 - [`@include`](./decorators.md#@Azure.ClientGenerator.Core.include)
 - [`@internal`](./decorators.md#@Azure.ClientGenerator.Core.internal)
 - [`@operationGroup`](./decorators.md#@Azure.ClientGenerator.Core.operationGroup)

packages/typespec-client-generator-core/README.md

@@ -19,6 +19,7 @@ npm install @azure-tools/typespec-client-generator-core
 - [`@convenientAPI`](#@convenientapi)
 - [`@exclude`](#@exclude)
 - [`@flattenProperty`](#@flattenproperty)
+- [`@hasJsonConverter`](#@hasjsonconverter)
 - [`@include`](#@include)
 - [`@internal`](#@internal)
 - [`@operationGroup`](#@operationgroup)
@@ -371,6 +372,33 @@ model Foo {
 model Bar {}
 ```
 
+#### `@hasJsonConverter`
+
+Whether a model needs the custom JSON converter, this is only used for backward compatibility for csharp.
+
+```typespec
+@Azure.ClientGenerator.Core.hasJsonConverter(scope?: valueof string)
+```
+
+##### Target
+
+`Model`
+
+##### Parameters
+
+| Name  | Type             | Description                                                                                                   |
+| ----- | ---------------- | ------------------------------------------------------------------------------------------------------------- |
+| scope | `valueof string` | The language scope you want this decorator to apply to. If not specified, will apply to all language emitters |
+
+##### Examples
+
+```typespec
+@hasJsonConverter
+model MyModel {
+  prop: string;
+}
+```
+
 #### `@include`
 
 _Deprecated: @include decorator is deprecated. Use `@usage` and `@access` decorator instead._

packages/typespec-client-generator-core/generated-defs/Azure.ClientGenerator.Core.ts

@@ -483,3 +483,21 @@ export type OverrideDecorator = (
   override: Operation,
   scope?: string
 ) => void;
+
+/**
+ * Whether a model needs the custom JSON converter, this is only used for backward compatibility for csharp.
+ *
+ * @param scope The language scope you want this decorator to apply to. If not specified, will apply to all language emitters
+ * @example
+ * ```typespec
+ * @hasJsonConverter
+ * model MyModel {
+ *   prop: string;
+ * }
+ * ```
+ */
+export type HasJsonConverterDecorator = (
+  context: DecoratorContext,
+  target: Model,
+  scope?: string
+) => void;

packages/typespec-client-generator-core/generated-defs/Azure.ClientGenerator.Core.ts-test.ts

@@ -7,6 +7,7 @@ import {
   $convenientAPI,
   $exclude,
   $flattenProperty,
+  $hasJsonConverter,
   $include,
   $internal,
   $operationGroup,
@@ -22,6 +23,7 @@ import type {
   ConvenientAPIDecorator,
   ExcludeDecorator,
   FlattenPropertyDecorator,
+  HasJsonConverterDecorator,
   IncludeDecorator,
   InternalDecorator,
   OperationGroupDecorator,
@@ -44,6 +46,7 @@ type Decorators = {
   $access: AccessDecorator;
   $flattenProperty: FlattenPropertyDecorator;
   $override: OverrideDecorator;
+  $hasJsonConverter: HasJsonConverterDecorator;
 };
 
 /** An error here would mean that the exported decorator is not using the same signature. Make sure to have export const $decName: DecNameDecorator = (...) => ... */
@@ -61,4 +64,5 @@ const _: Decorators = {
   $access,
   $flattenProperty,
   $override,
+  $hasJsonConverter,
 };

packages/typespec-client-generator-core/lib/decorators.tsp

@@ -467,3 +467,17 @@ extern dec flattenProperty(target: ModelProperty, scope?: valueof string);
  * ```
  */
 extern dec override(original: Operation, override: Operation, scope?: valueof string);
+
+/**
+ * Whether a model needs the custom JSON converter, this is only used for backward compatibility for csharp.
+ * @param scope The language scope you want this decorator to apply to. If not specified, will apply to all language emitters
+ *
+ * @example
+ * ```typespec
+ * @hasJsonConverter
+ * model MyModel {
+ *   prop: string;
+ * }
+ * ```
+ */
+extern dec hasJsonConverter(target: Model, scope?: valueof string);

packages/typespec-client-generator-core/src/decorators.ts

@@ -1135,3 +1135,9 @@ export function getOverriddenClientMethod(
 ): Operation | undefined {
   return getScopedDecoratorData(context, overrideKey, entity);
 }
+
+export const $hasJsonConverter: DecoratorFunction = (
+  context: DecoratorContext,
+  entity: Model,
+  scope?: LanguageScopes
+) => {};

packages/typespec-client-generator-core/test/types/general-decorators-list.test.ts

@@ -327,4 +327,29 @@ describe("typespec-client-generator-core: general decorators list", () => {
       ]);
     });
   });
+
+  describe("csharp only decorator", () => {
+    it("@hasJsonConverter", async function () {
+      runner = await createSdkTestRunner(
+        {},
+        { additionalDecorators: ["Azure\\.ClientGenerator\\.Core\\.@hasJsonConverter"] }
+      );
+
+      await runner.compileWithBuiltInService(`
+        @hasJsonConverter("csharp")
+        model A {
+          id: string;
+        }
+
+        op test(): A;
+      `);
+
+      const models = runner.context.sdkPackage.models;
+      strictEqual(models.length, 1);
+      deepStrictEqual(models[0].decorators, [
+        { name: "Azure.ClientGenerator.Core.@hasJsonConverter", arguments: { scope: "csharp" } },
+      ]);
+      expectDiagnostics(runner.context.diagnostics, []);
+    });
+  });
 });