fix(json-schema): recognize $defs when deriving type names

packages/quicktype-core/src/input/JSONSchemaInput.ts

@@ -306,7 +306,7 @@ export class Ref {
     public get definitionName(): string | undefined {
         const pe = arrayGetFromEnd(this.path, 2);
         if (pe === undefined) return undefined;
-        if (keyOrIndex(pe) === "definitions")
+        if (keyOrIndex(pe) === "definitions" || keyOrIndex(pe) === "$defs")
             return keyOrIndex(defined(arrayLast(this.path)));
         return undefined;
     }

test/inputs/schema/light.1.json

@@ -0,0 +1,7 @@
+{
+  "LightParams": {
+    "outlet_id": "outlet-1",
+    "app_id": "app-1",
+    "rgba": "255,255,255,1"
+  }
+}

test/inputs/schema/light.schema

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$defs": {
+    "LightParams": {
+      "type": "object",
+      "properties": {
+        "outlet_id": { "type": "string" },
+        "app_id": { "type": "string" },
+        "rgba": { "type": "string" }
+      },
+      "additionalProperties": false,
+      "required": ["outlet_id", "app_id", "rgba"]
+    }
+  },
+  "type": "object",
+  "properties": {
+    "LightParams": { "$ref": "#/$defs/LightParams" }
+  },
+  "additionalProperties": false,
+  "required": ["LightParams"]
+}

test/unit/json-schema-definitions.test.ts

@@ -0,0 +1,51 @@
+import {
+    FetchingJSONSchemaStore,
+    InputData,
+    JSONSchemaInput,
+    quicktype,
+} from "quicktype-core";
+import { expect, test } from "vitest";
+
+const lightSchema = {
+    $schema: "https://json-schema.org/draft/2020-12/schema",
+    $defs: {
+        LightParams: {
+            type: "object",
+            properties: {
+                outlet_id: { type: "string" },
+                app_id: { type: "string" },
+                rgba: { type: "string" },
+            },
+            additionalProperties: false,
+            required: ["outlet_id", "app_id", "rgba"],
+        },
+    },
+    type: "object",
+    properties: {
+        LightParams: { $ref: "#/$defs/LightParams" },
+    },
+    additionalProperties: false,
+    required: ["LightParams"],
+};
+
+test("a type under $defs keeps its definition name (issue #2778)", async () => {
+    const schemaInput = new JSONSchemaInput(new FetchingJSONSchemaStore());
+    await schemaInput.addSource({
+        name: "LightSchema",
+        schema: JSON.stringify(lightSchema),
+    });
+    const inputData = new InputData();
+    inputData.addInput(schemaInput);
+
+    const result = await quicktype({
+        inputData,
+        lang: "typescript",
+        rendererOptions: { "just-types": "true" },
+    });
+    const output = result.lines.join("\n");
+
+    // The fixture exercises this schema end-to-end, but generated symbol names
+    // are not observable at runtime, so assert the regression here.
+    expect(output).toContain("LightParams: LightParams;");
+    expect(output).toContain("export interface LightParams {");
+});