feat(tcgc): throw error when trying to flattening a model with polymo…

…rphsim resolve #959
Azure · Jul 23, 2024 · 4e6dfa4 · 4e6dfa4
1 parent 5362d7c
commit 4e6dfa4
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diff --git a/packages/typespec-client-generator-core/src/decorators.ts b/packages/typespec-client-generator-core/src/decorators.ts
@@ -17,6 +17,7 @@ import {
   Type,
   Union,
   createDiagnosticCollector,
+  getDiscriminator,
   getNamespaceFullName,
   getProjectedName,
   ignoreDiagnostics,
@@ -991,6 +992,13 @@ export const $flattenProperty: FlattenPropertyDecorator = (
   target: ModelProperty,
   scope?: LanguageScopes
 ) => {
+  if (getDiscriminator(context.program, target)) {
+    reportDiagnostic(context.program, {
+      code: "flatten-polymorphism",
+      format: {},
+      target: target,
+    });
+  }
   setScopedDecoratorData(context, $flattenProperty, flattenPropertyKey, target, true, scope); // eslint-disable-line deprecation/deprecation
 };
 

diff --git a/packages/typespec-client-generator-core/src/lib.ts b/packages/typespec-client-generator-core/src/lib.ts
@@ -166,6 +166,12 @@ export const $lib = createTypeSpecLibrary({
         nonDecorator: paramMessage`Client name: "${"name"}" is defined somewhere causing nameing conflicts in language scope: "${"scope"}"`,
       },
     },
+    "flatten-polymorphism": {
+      severity: "error",
+      messages: {
+        default: `Flattening polymorphic types is not supported.`,
+      },
+    },
   },
 });
 

diff --git a/packages/typespec-client-generator-core/test/decorators.test.ts b/packages/typespec-client-generator-core/test/decorators.test.ts
@@ -2545,6 +2545,33 @@ describe("typespec-client-generator-core: decorators", () => {
         code: "decorator-wrong-target",
       });
     });
+
+    it("throws error when used on a polymorphism type", async () => {
+      const diagnostics = await runner.diagnose(`
+        @service({})
+        @test namespace MyService {
+          @test
+          model Model1{
+            @flattenProperty
+            child: Model2;
+          }
+
+          @test
+          @discriminator("kind")
+          model Model2{
+            kind: string;
+          }
+
+          @test
+          @route("/func1")
+          op func1(@body body: Model1): void;
+        }
+      `);
+
+      expectDiagnostics(diagnostics, {
+        code: "flatten-polymorphism",
+      });
+    });
   });
 
   describe("@clientName", () => {