fix(v4): allow dynamic .catch() under unrepresentable: "any" (#5273) (#5925)

`catchProcessor` evaluates `def.catchValue(undefined)` to derive a static `default`. When the callback inspects its `ctx` argument it throws, and `z.toJSONSchema()` surfaced that as a hard error even when the caller opted into lossy conversion.

Gate the rethrow on `unrepresentable === "throw"`. Under `"any"`, skip the `default` and fall through with the inner schema (already populated by the preceding `process(def.innerType)` call) — same passthrough shape `pipe(transform, ...)` produces today.

Default behaviour is unchanged. Adds a snapshot test for the new path.

Author: dokson

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

@@ -325,6 +325,12 @@ describe("toJSONSchema", () => {
     // Dynamic catch values
     const dynamicCatchSchema = z.string().catch((ctx) => `${ctx.issues.length}`);
     expect(() => z.toJSONSchema(dynamicCatchSchema)).toThrow("Dynamic catch values are not supported in JSON Schema");
+    expect(z.toJSONSchema(dynamicCatchSchema, { unrepresentable: "any" })).toMatchInlineSnapshot(`
+      {
+        "$schema": "https://json-schema.org/draft/2020-12/schema",
+        "type": "string",
+      }
+    `);
   });
 
   test("string formats", () => {

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

@@ -518,7 +518,10 @@ export const catchProcessor: Processor<schemas.$ZodCatch> = (schema, ctx, json,
   try {
     catchValue = def.catchValue(undefined as any);
   } catch {
-    throw new Error("Dynamic catch values are not supported in JSON Schema");
+    if (ctx.unrepresentable === "throw") {
+      throw new Error("Dynamic catch values are not supported in JSON Schema");
+    }
+    return;
   }
   json.default = catchValue;
 };