toJSONSchema throws on a schema with both a refinement and a toJSONSchema override (4.3.0 regression) #6741

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1. manav4u commented on Nov 7, 2026

   

   manav4u

   on Nov 7, 2026

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   I reproduced this on current main (19c40d2). There is one related case worth covering when fixing it: if the parent is also present elsewhere in the schema and has an id, it is already in ctx.seen, so an undefined guard alone still lets the parent's $ref leak into the custom override.

   const parent = z.string().meta({ id: "Parent" });
   const child = parent.min(1);
   child._zod.toJSONSchema = () => ({ type: "integer", title: "override" });
   
   console.log(z.toJSONSchema(z.object({ parent, child })));

   The child currently becomes { type: "integer", title: "override", $ref: "#/$defs/Parent" }, while Parent requires a string. It happens in both property orders. The custom schema should not inherit that reference.

   A private candidate that records the custom override and skips only its parent-inheritance step covers both cases while still running the final override callback. The three new regression tests fail on the baseline and pass with that change. Local validation: 2,308 V4 runtime tests across 137 files, plus changed-file Biome and a standalone source TypeScript check. This used Node 22 and Vitest 4.0.18 with a source-alias test harness, not the repository's Node 24/Nub setup, so it is not a full upstream CI result.

   Sharing this as a supplementary finding for your fix, rather than opening a competing PR. Investigation and tests were AI-assisted.
2. HuluWZ commented on Nov 9, 2026

   

   HuluWZ

   on Nov 9, 2026

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   Reproduced on main. The cause is that a schema with an override and a parent never registers the parent in seen, so flattenRef throws
   on the missing entry. A guard in flattenRef fixes the throw, but a parent with an id still leaks its $ref into the override (the case manav4u noted above), so I marked the override as already flattened instead (result.ref = null in processSchema).

   Fix and regression test (both property orders, parent with an id): https://github.com/HuluWZ/zod/tree/fix-6741. I can't open a PR
   because pull requests are limited to collaborators, so feel free to cherry-pick 899d78c.
3. manav4u commented on Nov 9, 2026

   

   manav4u

   on Nov 9, 2026

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   Thanks for covering the parent-id case. One compatibility case is still worth checking in 899d78c2: setting result.ref = null also makes flattenRef return before the final options.override callback.

   const schema = z.string();
   schema._zod.toJSONSchema = () => ({ type: "integer" });
   let calls = 0;
   const result = z.toJSONSchema(schema, {
     override: ({ jsonSchema }) => {
       calls++;
       jsonSchema.description = "final override";
     },
   });
   console.log(calls, result.description);

   On your commit this prints 0, undefined; on its parent it prints 1, "final override". The same callback is skipped for a refined custom schema after the fix. A regression should keep that callback running while preventing parent-reference inheritance, rather than marking the whole schema already finalized.

   Checked locally with Node 22 and a source-import harness, not upstream CI. Investigation was AI-assisted. Sharing this for your fix, not opening a competing PR.
4. HuluWZ commented on Nov 9, 2026

   

   HuluWZ

   on Nov 9, 2026

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   Thanks, that was a real bug: result.ref = null made flattenRef return before the final options.override callback ran. I reproduced it (0 calls, no description). The custom schema is now flagged instead, and flattenRef skips only the parent-inheritance step. The callback runs once again, and the parent-with-id case still works. Your snippet is added to the regression test.

   Both commits are on the branch: https://github.com/HuluWZ/zod/tree/fix-6741 (899d78c2 and cdb45448).