Flatten simple intersections

Author: colinhacks

packages/zod/src/v4/classic/tests/to-json-schema.test.ts

@@ -1981,3 +1981,69 @@ test("use output type for preprocess", () => {
 //   const d = z.string().default("hello");
 //   expect(tx(d)).toEqual(false);
 // });
+
+test("flatten simple intersections", () => {
+  const FirstSchema = z.object({
+    testNum: z.number(),
+  });
+
+  const SecondSchema = z.object({
+    testStr: z.string(),
+  });
+
+  const ThirdSchema = z.object({
+    testBool: z.boolean(),
+  });
+
+  const HelloSchema = FirstSchema.and(SecondSchema).and(ThirdSchema).describe("123");
+
+  // Zod 3
+  // console.log(JSON.stringify(zodToJsonSchema(HelloSchema), null, 2));
+
+  // Zod 4
+  const result = z.toJSONSchema(HelloSchema, { target: "draft-7" });
+  expect(result).toMatchInlineSnapshot(`
+    {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "allOf": [
+        {
+          "additionalProperties": false,
+          "properties": {
+            "testNum": {
+              "type": "number",
+            },
+          },
+          "required": [
+            "testNum",
+          ],
+          "type": "object",
+        },
+        {
+          "additionalProperties": false,
+          "properties": {
+            "testStr": {
+              "type": "string",
+            },
+          },
+          "required": [
+            "testStr",
+          ],
+          "type": "object",
+        },
+        {
+          "additionalProperties": false,
+          "properties": {
+            "testBool": {
+              "type": "boolean",
+            },
+          },
+          "required": [
+            "testBool",
+          ],
+          "type": "object",
+        },
+      ],
+      "description": "123",
+    }
+  `);
+});

packages/zod/src/v4/core/to-json-schema.ts

@@ -105,8 +105,6 @@ export class JSONSchemaGenerator {
         seen.cycle = _params.path;
       }
 
-      seen.count++;
-      // break cycle
       return seen.schema;
     }
 
@@ -320,16 +318,21 @@ export class JSONSchemaGenerator {
         }
         case "intersection": {
           const json: JSONSchema.BaseSchema = _json as any;
-          json.allOf = [
-            this.process(def.left, {
-              ...params,
-              path: [...params.path, "allOf", 0],
-            }),
-            this.process(def.right, {
-              ...params,
-              path: [...params.path, "allOf", 1],
-            }),
+          const a = this.process(def.left, {
+            ...params,
+            path: [...params.path, "allOf", 0],
+          });
+          const b = this.process(def.right, {
+            ...params,
+            path: [...params.path, "allOf", 1],
+          });
+
+          const isSimpleIntersection = (val: any) => "allOf" in val && Object.keys(val).length === 1;
+          const allOf = [
+            ...(isSimpleIntersection(a) ? (a.allOf as any[]) : [a]),
+            ...(isSimpleIntersection(b) ? (b.allOf as any[]) : [b]),
           ];
+          json.allOf = allOf;
           break;
         }
         case "tuple": {

play.ts

@@ -1,17 +1,19 @@
 import { z } from "zod/v4";
 
-// export type ClickCallbackArgs = z.infer<typeof ClickCallbackArgsSchema>;
+const FirstSchema = z.object({
+  testNum: z.number(),
+});
 
-const myFunction = z.function({
-  input: [
-    z.object({
-      name: z.string(),
-      age: z.number().int(),
-    }),
-  ],
-  output: z.string(),
+const SecondSchema = z.object({
+  testStr: z.string(),
 });
 
-myFunction.implement((args) => {
-  return `${args.age}`;
+const ThirdSchema = z.object({
+  testBool: z.boolean(),
 });
+
+const HelloSchema = FirstSchema.and(SecondSchema).and(ThirdSchema).describe("123");
+
+// Zod 4
+const result = z.toJSONSchema(HelloSchema, { target: "draft-7" });
+console.dir(result, { depth: null });