Fix circular reference not always inlining array properties (#2810)

fix #2796

.changeset/rich-grapes-wink.md

@@ -0,0 +1,5 @@
+---
+"@typespec/openapi3": patch
+---
+
+Fix circular reference would not always inline array properties

packages/openapi3/package.json

@@ -38,6 +38,7 @@
     "watch": "tsc -p . --watch",
     "lint-typespec-library": "tsp compile . --warn-as-error --import @typespec/library-linter --no-emit",
     "test": "vitest run",
+    "test:watch": "vitest -w",
     "test:ui": "vitest --ui",
     "test-official": "vitest run --coverage --reporter=junit --reporter=default --no-file-parallelism",
     "lint": "eslint . --ext .ts --max-warnings=0",

packages/openapi3/src/schema-emitter.ts

@@ -355,7 +355,7 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     // Attach any additional OpenAPI extensions
     this.#attachExtensions(program, prop, additionalProps);
 
-    if (schema && isRef) {
+    if (schema && isRef && !(prop.type.kind === "Model" && isArrayModelType(program, prop.type))) {
       if (Object.keys(additionalProps).length === 0) {
         return schema;
       } else {
@@ -370,7 +370,7 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
         delete schema.anyOf;
       }
 
-      const merged = new ObjectBuilder(schema);
+      const merged = ensureObjectBuilder(schema);
       for (const [key, value] of Object.entries(additionalProps)) {
         merged.set(key, value);
       }
@@ -947,6 +947,16 @@ function includeDerivedModel(model: Model): boolean {
   );
 }
 
+function ensureObjectBuilder<
+  T extends Record<string, unknown> | Placeholder<Record<string, unknown>> | undefined,
+>(type: T | ObjectBuilder<T>): ObjectBuilder<T> {
+  if (type instanceof ObjectBuilder) {
+    return type;
+  } else {
+    return new ObjectBuilder(type);
+  }
+}
+
 const B = {
   array: <T>(items: T[]): ArrayBuilder<T> => {
     const builder = new ArrayBuilder<T>();

packages/openapi3/test/array.test.ts

@@ -1,6 +1,6 @@
 import { deepStrictEqual, ok, strictEqual } from "assert";
 import { describe, it } from "vitest";
-import { oapiForModel } from "./test-host.js";
+import { oapiForModel, openApiFor } from "./test-host.js";
 
 describe("openapi3: Array", () => {
   it("defines array inline", async () => {
@@ -19,6 +19,37 @@ describe("openapi3: Array", () => {
     });
   });
 
+  it("keeps array inline in circular reference with extra properties", async () => {
+    const res = await openApiFor(
+      `
+      model Root {
+        value: Parent[];
+      }
+
+      model Parent {
+        @OpenAPI.extension("x-someFieldAttr", true)
+        children?: Child[];
+      }
+
+      model Child {
+        @OpenAPI.extension("x-someFieldAttr", true)
+        parents?: Parent[];
+      }
+      `
+    );
+
+    deepStrictEqual(res.components.schemas.Parent.properties.children, {
+      type: "array",
+      items: { $ref: "#/components/schemas/Child" },
+      "x-someFieldAttr": true,
+    });
+    deepStrictEqual(res.components.schemas.Child.properties.parents, {
+      type: "array",
+      items: { $ref: "#/components/schemas/Parent" },
+      "x-someFieldAttr": true,
+    });
+  });
+
   it("define a named array using model is", async () => {
     const res = await oapiForModel(
       "Pet",