External fields (for objects and tuples) about valita

[jviide]

I think this can be achieved with Valita's builtin features by using the strict parsing mode and inferring the Parent and Child types from the final parser:

const Parent = v.object({
  children: v
    .record(
      v.object({
        color: v.string(),
      })
    )
    .map((children) =>
      Object.fromEntries(
        Object.entries(children).map(([name, child]) => [
          name,
          { name, ...child },
        ])
      )
    ),
});

type Parent = v.Infer<typeof Parent>;
type Child = Parent["children"][string];

const example = Parent.parse(someInput, { mode: "strict" });

The strict mode makes Valita fail parsing when it encounters an unexpected object key:

Parent.parse(
  {
    children: { alice: { color: "blue", name: "bob" } },
  },
  { mode: "strict" }
);
// ValitaError: unrecognized_key at .children.alice (unrecognized key "name")

In fact, since Valita v0.0.21 released yesterday, the strict mode is the default (the old behavior can be enabled by setting { mode: "passthrough" }):

Parent.parse({
  children: { alice: { color: "blue", name: "bob" } },
});
// ValitaError: unrecognized_key at .children.alice (unrecognized key "name")

It's also possible for v.object to "opt-in" to strict parsing regardless of the parsing mode:

      // fail parsing if "name" is present.
      v.object({
        color: v.string(),
        name: v.never().optional()
      })

or

      // fail parsing if "color" is not the only key present
      v.object({
        color: v.string(),
      })
      .rest(v.never())

[jviide]

I'm assuming this was solved, so closing this issue 👍