fix: preserve explicit superRefine issue input (#6053)

`_issue.input ??= payload.value` discarded an explicitly-supplied nullish `input`, so `superRefine` was the one place in Zod that could not emit an issue whose `input` matched the value-at-the-path convention every builtin issue follows. Forwarding a nested parse's issues was worse: an inner `input: undefined` for a missing key got overwritten with the outer payload, which breaks the documented `iss.input === undefined` test for a missing field.

Switching to a presence check preserves an explicit `null` or `undefined` while still backfilling when `input` is omitted. `undefined` is a meaningful value for `input` in a way it isn't for the `code`/`inst`/`continue` defaults alongside it, which is why only this one moves off `??=`.

Costs 26 B raw in classic, 0 B in mini unless `z.superRefine` is imported. No memory change, and the line only runs when an issue is constructed.

Author: frastefanini

packages/zod/src/v4/classic/schemas.ts

@@ -2199,7 +2199,7 @@ export const ZodTransform: core.$constructor<ZodTransform> = /*@__PURE__*/ core.
 
           if (_issue.fatal) _issue.continue = false;
           _issue.code ??= "custom";
-          _issue.input ??= payload.value;
+          if (!("input" in _issue)) _issue.input = payload.value;
           _issue.inst ??= inst;
           // _issue.continue ??= true;
           payload.issues.push(util.issue(_issue));

packages/zod/src/v4/classic/tests/index.test.ts

@@ -735,6 +735,26 @@ test("z.refine", () => {
   expect(() => z.parse(a, "hi")).toThrow();
 });
 
+test("z.superRefine preserves explicit nullish issue input", () => {
+  const schema = z.string().check(
+    z.superRefine((_, ctx) => {
+      ctx.addIssue({ code: "custom", message: "default" });
+      ctx.addIssue({ code: "custom", message: "null", input: null });
+      ctx.addIssue({ code: "custom", message: "undefined", input: undefined });
+    })
+  );
+
+  const result = z.safeParse(schema, "sensitive", { reportInput: true });
+  expect(result.success).toEqual(false);
+  if (!result.success) {
+    expect(result.error.issues).toHaveLength(3);
+    expect(result.error.issues[0].input).toEqual("sensitive");
+    expect(result.error.issues[1].input).toEqual(null);
+    expect(result.error.issues[2]).toHaveProperty("input");
+    expect(result.error.issues[2].input).toEqual(undefined);
+  }
+});
+
 // test("z.superRefine", () => {
 //   const a = z.number([
 //     z.superRefine((val, ctx) => {

packages/zod/src/v4/classic/tests/refine.test.ts

@@ -338,6 +338,24 @@ describe("superRefine functionality", () => {
     }
   });
 
+  test("should preserve explicit nullish issue input", () => {
+    const schema = z.string().superRefine((_, ctx) => {
+      ctx.addIssue({ code: "custom", message: "default" });
+      ctx.addIssue({ code: "custom", message: "null", input: null });
+      ctx.addIssue({ code: "custom", message: "undefined", input: undefined });
+    });
+
+    const result = schema.safeParse("sensitive", { reportInput: true });
+    expect(result.success).toEqual(false);
+    if (!result.success) {
+      expect(result.error.issues).toHaveLength(3);
+      expect(result.error.issues[0].input).toEqual("sensitive");
+      expect(result.error.issues[1].input).toEqual(null);
+      expect(result.error.issues[2]).toHaveProperty("input");
+      expect(result.error.issues[2].input).toEqual(undefined);
+    }
+  });
+
   test("should respect fatal flag in superRefine", () => {
     const schema = z
       .string()

packages/zod/src/v4/core/api.ts

@@ -1686,7 +1686,7 @@ export function _superRefine<T>(
         const _issue: any = issue;
         if (_issue.fatal) _issue.continue = false;
         _issue.code ??= "custom";
-        _issue.input ??= payload.value;
+        if (!("input" in _issue)) _issue.input = payload.value;
         _issue.inst ??= ch;
         _issue.continue ??= !ch._zod.def.abort; // abort is always undefined, so this is always true...
         payload.issues.push(util.issue(_issue));