fix(langchain): Fix toJsonSchema mutating underlying zod schema

Author: ro0sterjam

langchain-core/src/utils/json_schema.ts

@@ -5,10 +5,8 @@ import {
   isZodSchemaV3,
   isZodSchemaV4,
   InteropZodType,
-  interopZodObjectStrict,
-  isZodObjectV4,
-  ZodObjectV4,
-  interopZodTransformInputSchema,
+  ZodTypeV4,
+  interopZodSanitizeSchema,
 } from "./types/zod.js";
 
 export type JSONSchema = JsonSchema7Type;
@@ -22,16 +20,8 @@ export { deepCompareStrict, Validator } from "@cfworker/json-schema";
  */
 export function toJsonSchema(schema: InteropZodType | JSONSchema): JSONSchema {
   if (isZodSchemaV4(schema)) {
-    const inputSchema = interopZodTransformInputSchema(schema, true);
-    if (isZodObjectV4(inputSchema)) {
-      const strictSchema = interopZodObjectStrict(
-        inputSchema,
-        true
-      ) as ZodObjectV4;
-      return toJSONSchema(strictSchema);
-    } else {
-      return toJSONSchema(schema);
-    }
+    const inputSchema = interopZodSanitizeSchema(schema, true);
+    return toJSONSchema(inputSchema as ZodTypeV4);
   }
   if (isZodSchemaV3(schema)) {
     return zodToJsonSchema(schema);

langchain-core/src/utils/types/tests/zod.test.ts

@@ -1525,6 +1525,48 @@ describe("Zod utility functions", () => {
         expect(elementShape.name).toBeInstanceOf(z4.ZodString);
         expect(elementShape.age).toBeInstanceOf(z4.ZodNumber);
       });
+
+      it("should not mutate the original schema when object", () => {
+        const inputSchema = z4.object({
+          user: z4.object({
+            name: z4.string().transform((s) => s.toUpperCase()),
+            age: z4.number().transform((n) => n * 2),
+          }),
+        });
+
+        const result = interopZodTransformInputSchema(inputSchema, true);
+
+        expect(result).not.toBe(inputSchema);
+        expect(inputSchema.shape.user.shape.name).toBeInstanceOf(z4.ZodPipe);
+        expect(inputSchema.shape.user.shape.age).toBeInstanceOf(z4.ZodPipe);
+        expect((result as z4.ZodObject).shape.user.shape.name).toBeInstanceOf(
+          z4.ZodString
+        );
+        expect((result as z4.ZodObject).shape.user.shape.age).toBeInstanceOf(
+          z4.ZodNumber
+        );
+      });
+
+      it("should not mutate the original schema when array", () => {
+        const inputSchema = z4.array(
+          z4.object({
+            name: z4.string().transform((s) => s.toUpperCase()),
+            age: z4.number().transform((n) => n * 2),
+          })
+        );
+
+        const result = interopZodTransformInputSchema(inputSchema, true);
+
+        expect(result).not.toBe(inputSchema);
+        expect(inputSchema.element.shape.name).toBeInstanceOf(z4.ZodPipe);
+        expect(inputSchema.element.shape.age).toBeInstanceOf(z4.ZodPipe);
+        expect(
+          ((result as z4.ZodArray).element as z4.ZodObject).shape.name
+        ).toBeInstanceOf(z4.ZodString);
+        expect(
+          ((result as z4.ZodArray).element as z4.ZodObject).shape.age
+        ).toBeInstanceOf(z4.ZodNumber);
+      });
     });
 
     it("should throw error for non-schema values", () => {

langchain-core/src/utils/types/zod.ts

@@ -23,6 +23,8 @@ export type ZodObjectV3 = z3.ZodObject<any, any, any, any>;
 
 export type ZodObjectV4 = z4.$ZodObject;
 
+export type ZodTypeV4 = z4.$ZodType;
+
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export type InteropZodType<Output = any, Input = Output> =
   | z3.ZodType<Output, z3.ZodTypeDef, Input>
@@ -748,7 +750,9 @@ export function interopZodTransformInputSchema(
     if (recursive) {
       // Handle nested object schemas
       if (isZodObjectV4(outputSchema)) {
-        const outputShape: Mutable<z4.$ZodShape> = outputSchema._zod.def.shape;
+        const outputShape: Mutable<z4.$ZodShape> = {
+          ...outputSchema._zod.def.shape,
+        };
         for (const [key, keySchema] of Object.entries(
           outputSchema._zod.def.shape
         )) {
@@ -781,3 +785,27 @@ export function interopZodTransformInputSchema(
 
   throw new Error("Schema must be an instance of z3.ZodType or z4.$ZodType");
 }
+
+/**
+ * Sanitizes a Zod schema by transforming it to its input schema and then making it strict.
+ * Supports both Zod v3 and v4 schemas. If `recursive` is true, applies strictness recursively to all nested object schemas and arrays of object schemas.
+ *
+ * @param schema - The Zod schema instance (v3 or v4)
+ * @param {boolean} [recursive=false] - Whether to recursively process nested objects/arrays.
+ * @returns The sanitized Zod schema.
+ */
+export function interopZodSanitizeSchema(
+  schema: InteropZodType,
+  recursive: boolean = false
+): InteropZodType {
+  const inputSchema = interopZodTransformInputSchema(schema, recursive);
+  if (isZodObjectV4(inputSchema)) {
+    const strictSchema = interopZodObjectStrict(
+      inputSchema,
+      recursive
+    ) as ZodObjectV4;
+    return strictSchema;
+  } else {
+    return inputSchema;
+  }
+}

libs/langchain-openai/src/chat_models.ts

@@ -71,6 +71,7 @@ import {
   getSchemaDescription,
   InteropZodType,
   isInteropZodSchema,
+  interopZodSanitizeSchema,
 } from "@langchain/core/utils/types";
 import { toJsonSchema } from "@langchain/core/utils/json_schema";
 import {
@@ -1242,7 +1243,9 @@ export abstract class BaseChatOpenAI<
       const openaiJsonSchemaParams = {
         name: name ?? "extract",
         description: getSchemaDescription(schema),
-        schema,
+        schema: isInteropZodSchema(schema)
+          ? interopZodSanitizeSchema(schema, true)
+          : schema,
         strict: config?.strict,
       };
       const asJsonSchema = toJsonSchema(openaiJsonSchemaParams.schema);