fix(openapi3): Fix duplicate type name error for unreachable derived models with visibility properties

.chronus/changes/fix-duplicate-type-name-visibility-2026-7-28.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Fix duplicate type name error when a model with a `@visibility(Lifecycle.Create, Lifecycle.Update)` property extends another model.

packages/openapi3/src/schema-emitter.ts

@@ -222,7 +222,13 @@ export class OpenAPI3SchemaEmitterBase<
     const derivedModels = model.derivedModels.filter(includeDerivedModel);
     // getSchemaOrRef on all children to push them into components.schemas
     for (const child of derivedModels) {
-      this.emitter.emitTypeReference(child);
+      if (this._visibilityUsage.isUnreachable(child)) {
+        // Unreachable derived models will be emitted by processUnreferencedSchemas with
+        // Visibility.All context. Force the same context here to avoid a duplicate declaration.
+        this.emitter.emitTypeReference(child, { referenceContext: { visibility: Visibility.All } });
+      } else {
+        this.emitter.emitTypeReference(child);
+      }
     }
 
     this.applyDiscriminator(model, schema as any);

packages/openapi3/test/metadata.test.ts

@@ -1215,6 +1215,33 @@ worksFor(supportedVersions, ({ openApiFor }) => {
       required: ["name"],
     });
   });
+
+  it("inheritance tree unreachable with @visibility(Create, Update) property doesn't get conflicts", async () => {
+    const res = await openApiFor(`
+      model Base {
+      }
+
+      model Child extends Base {
+        @visibility(Lifecycle.Create, Lifecycle.Update) name: string;
+      }
+    `);
+
+    deepStrictEqual(Object.keys(res.components.schemas), ["Base", "Child"]);
+    deepStrictEqual(res.components.schemas.Child, {
+      type: "object",
+      allOf: [
+        {
+          $ref: "#/components/schemas/Base",
+        },
+      ],
+      properties: {
+        name: {
+          type: "string",
+        },
+      },
+      required: ["name"],
+    });
+  });
 });
 
 worksFor(["3.0.0"], ({ openApiFor }) => {