From 691e0b3eca155d83e32f0b8520adc2cdb3339c07 Mon Sep 17 00:00:00 2001
From: unnoq <contact@unnoq.com>
Date: Mon, 29 Dec 2025 16:10:15 +0700
Subject: [PATCH] feat(zod): enhance schema conversion logic for zod4
 preprocess

Fixes #1317
---
 packages/zod/src/zod4/converter.processed.test.ts |  6 ++++++
 packages/zod/src/zod4/converter.ts                | 10 +++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/packages/zod/src/zod4/converter.processed.test.ts b/packages/zod/src/zod4/converter.processed.test.ts
index 8feee8522..fc6d8032e 100644
--- a/packages/zod/src/zod4/converter.processed.test.ts
+++ b/packages/zod/src/zod4/converter.processed.test.ts
@@ -18,4 +18,10 @@ testSchemaConverter([
     input: [true, { type: 'string' }],
     output: [false, {}],
   },
+  {
+    name: 'preprocess(x => x, z.string())',
+    schema: z.preprocess(x => x, z.string()),
+    input: [true, { type: 'string' }],
+    output: [true, { type: 'string' }],
+  },
 ])
diff --git a/packages/zod/src/zod4/converter.ts b/packages/zod/src/zod4/converter.ts
index d25852a7f..9347b6242 100644
--- a/packages/zod/src/zod4/converter.ts
+++ b/packages/zod/src/zod4/converter.ts
@@ -519,7 +519,15 @@ export class ZodToJsonSchemaConverter implements ConditionalSchemaConverter {
 
           case 'pipe': {
             const pipe = schema as $ZodPipe
-            return this.#convert(options.strategy === 'input' ? pipe._zod.def.in : pipe._zod.def.out, options, lazyDepth, structureDepth)
+            return this.#convert(
+              // prefer out schema when in schema is preprocess/transform
+              options.strategy === 'input' && pipe._zod.def.in._zod.def.type !== 'transform'
+                ? pipe._zod.def.in
+                : pipe._zod.def.out,
+              options,
+              lazyDepth,
+              structureDepth,
+            )
           }
 
           case 'readonly': {