Summary

Closes #5625

Adds an .invert() method to ZodCodec (and ZodMiniCodec) that returns a new codec with swapped input/output schemas and swapped decode/encode transforms.

Usage

const isoDateCodec = z.codec(z.iso.datetime(), z.date(), {
  decode: (isoString) => new Date(isoString),
  encode: (date) => date.toISOString(),
});

// Inverted: Date → ISO string
const dateToIso = isoDateCodec.invert();

z.decode(dateToIso, new Date("2024-01-15T10:30:00.000Z"));
// → "2024-01-15T10:30:00.000Z"

z.encode(dateToIso, "2024-01-15T10:30:00.000Z");
// → Date object

This is useful when composing schemas in pipelines where the direction needs to be flipped — for example, form validation schemas in react-hook-form where the input type is string but the output should be a parsed value.

Implementation

The method creates a new codec with:

• def.in ↔ def.out swapped
• def.transform ↔ def.reverseTransform swapped

Zero runtime overhead — just a new instance with references swapped.

Files changed

• packages/zod/src/v4/classic/schemas.ts — ZodCodec interface + constructor
• packages/zod/src/v4/mini/schemas.ts — ZodMiniCodec interface + constructor
• packages/zod/src/v4/classic/tests/codec.test.ts — 5 new test cases

Test plan

• Basic invert: decode/encode directions swapped correctly
• Round trip: invert preserves data through decode→encode cycle
• Type inference: z.input/z.output types correctly swapped
• Double invert: .invert().invert() behaves like original
• Invert with pipe: works with piped schemas
• Full test suite passes (3585 tests, 0 type errors)
• Format and lint checks pass