From 89d9f2ad9fce42399a8b091fd87701ae45700447 Mon Sep 17 00:00:00 2001
From: Mark Probst <mark.probst@gmail.com>
Date: Mon, 20 Jul 2026 19:14:56 -0400
Subject: [PATCH] fix(cjson): start enum values at 1 so invalid/missing input
 is distinguishable (#2357)

Co-Authored-By: gpt-5.6-sol via pi <noreply@openai.com>
---
 .../src/language/CJSON/CJSONRenderer.ts       | 16 +++++++-
 test/unit/cjson-enum-default.test.ts          | 37 +++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 test/unit/cjson-enum-default.test.ts

diff --git a/packages/quicktype-core/src/language/CJSON/CJSONRenderer.ts b/packages/quicktype-core/src/language/CJSON/CJSONRenderer.ts
index c750529c98..442978d9e6 100644
--- a/packages/quicktype-core/src/language/CJSON/CJSONRenderer.ts
+++ b/packages/quicktype-core/src/language/CJSON/CJSONRenderer.ts
@@ -428,6 +428,7 @@ export class CJSONRenderer extends ConvenienceRenderer {
                 const combinedName = allUpperWordStyle(
                     this.sourcelikeToString(enumName),
                 );
+                let isFirst = true;
                 this.forEachEnumCase(enumType, "none", (name, jsonName) => {
                     if (enumValues !== undefined) {
                         const [enumValue] = getAccessorName(
@@ -444,11 +445,22 @@ export class CJSONRenderer extends ConvenienceRenderer {
                                 ",",
                             );
                         } else {
-                            this.emitLine(combinedName, "_", name, ",");
+                            this.emitLine(
+                                combinedName,
+                                "_",
+                                name,
+                                isFirst ? " = 1," : ",",
+                            );
                         }
                     } else {
-                        this.emitLine(combinedName, "_", name, ",");
+                        this.emitLine(
+                            combinedName,
+                            "_",
+                            name,
+                            isFirst ? " = 1," : ",",
+                        );
                     }
+                    isFirst = false;
                 });
             },
             "",
diff --git a/test/unit/cjson-enum-default.test.ts b/test/unit/cjson-enum-default.test.ts
new file mode 100644
index 0000000000..b2c02d60ee
--- /dev/null
+++ b/test/unit/cjson-enum-default.test.ts
@@ -0,0 +1,37 @@
+import { InputData, JSONSchemaInput, quicktype } from "quicktype-core";
+import { describe, expect, test } from "vitest";
+
+const schema = JSON.stringify({
+    $schema: "http://json-schema.org/draft-07/schema#",
+    type: "object",
+    properties: {
+        subscription: {
+            type: "string",
+            enum: ["state", "config", "heartbeat"],
+        },
+    },
+    required: ["subscription"],
+});
+
+async function cJSONOutput(): Promise<string> {
+    const schemaInput = new JSONSchemaInput(undefined);
+    await schemaInput.addSource({ name: "TopLevel", schema });
+    const inputData = new InputData();
+    inputData.addInput(schemaInput);
+
+    const result = await quicktype({ inputData, lang: "cjson" });
+    return result.lines.join("\n");
+}
+
+describe("cJSON enum invalid value", () => {
+    test("does not collide with a real enumerator", async () => {
+        const output = await cJSONOutput();
+
+        expect(output).toContain(`enum Subscription {
+    SUBSCRIPTION_CONFIG = 1,
+    SUBSCRIPTION_HEARTBEAT,
+    SUBSCRIPTION_STATE,
+};`);
+        expect(output).toContain("enum Subscription x = 0;");
+    });
+});