fix: printSchema in StructuredOutputParser failing when using Zod (#787)

* fix: printSchema failing when using Zod

* Fix lint

* Fix error message

---------

Co-authored-by: Nuno Campos <nuno@boringbits.io>

langchain/src/output_parsers/structured.ts

@@ -5,40 +5,53 @@ import { BaseOutputParser, OutputParserException } from "../schema/index.js";
 
 function printSchema(schema: z.ZodTypeAny, depth = 0): string {
   if (
-    schema instanceof z.ZodString &&
-    schema._def.checks.some((check) => check.kind === "datetime")
+    (schema instanceof z.ZodString || schema._def.typeName === "ZodString") &&
+    (schema as z.ZodString)._def.checks.some(
+      (check) => check.kind === "datetime"
+    )
   ) {
     return "datetime";
   }
-  if (schema instanceof z.ZodString) {
+  if (schema instanceof z.ZodString || schema._def.typeName === "ZodString") {
     return "string";
   }
-  if (schema instanceof z.ZodNumber) {
+  if (schema instanceof z.ZodNumber || schema._def.typeName === "ZodNumber") {
     return "number";
   }
-  if (schema instanceof z.ZodBoolean) {
+  if (schema instanceof z.ZodBoolean || schema._def.typeName === "ZodBoolean") {
     return "boolean";
   }
-  if (schema instanceof z.ZodDate) {
+  if (schema instanceof z.ZodDate || schema._def.typeName === "ZodDate") {
     return "date";
   }
-  if (schema instanceof z.ZodNullable) {
+  if (
+    schema instanceof z.ZodNullable ||
+    schema._def.typeName === "ZodNullable"
+  ) {
     return `${printSchema(schema._def.innerType, depth)} // Nullable`;
   }
-  if (schema instanceof z.ZodTransformer) {
+  if (
+    schema instanceof z.ZodTransformer ||
+    schema._def.typeName === "ZodTransformer"
+  ) {
     return `${printSchema(schema._def.schema, depth)}`;
   }
-  if (schema instanceof z.ZodOptional) {
+  if (
+    schema instanceof z.ZodOptional ||
+    schema._def.typeName === "ZodOptional"
+  ) {
     return `${printSchema(schema._def.innerType, depth)} // Optional`;
   }
-  if (schema instanceof z.ZodArray) {
+  if (schema instanceof z.ZodArray || schema._def.typeName === "ZodArray") {
     return `${printSchema(schema._def.type, depth)}[]`;
   }
-  if (schema instanceof z.ZodObject) {
+  if (schema instanceof z.ZodObject || schema._def.typeName === "ZodObject") {
     const indent = "\t".repeat(depth);
     const indentIn = "\t".repeat(depth + 1);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const { shape } = schema as z.ZodObject<any>;
     return `{${schema._def.description ? ` // ${schema._def.description}` : ""}
-${Object.entries(schema.shape)
+${Object.entries(shape)
   .map(
     ([key, value]) =>
       `${indentIn}"${key}": ${printSchema(value as z.ZodTypeAny, depth + 1)}${
@@ -51,7 +64,7 @@ ${Object.entries(schema.shape)
 ${indent}}`;
   }
 
-  throw new Error(`Unsupported type: ${schema._def.innerType.typeName}`);
+  throw new Error(`Unsupported type: ${schema._def.typeName}`);
 }
 
 export class StructuredOutputParser<