Throwing in S.transform isn't caught

[chenglou]

const a = S.string.with(S.transform, () => {
  throw new Error('hi')
})
S.safe(() => S.parseOrThrow('', a))

❯ bun test.ts 
1 | import * as S from 'sury'
2 | 
3 | const a = S.string.with(S.transform, () => {
4 |   throw new Error('hi')
            ^
error: hi
      at <anonymous> (...)

[chenglou]

Tell me if I'm using transform wrong btw. How related will it be to S.to in the future?

[DZakh]

Currently, you need to use the context object to report errors:

const a = S.string.with(S.transform, (input, s) => {
  throw s.fail('hi')
})
S.safe(() => S.parseOrThrow('', a))

Under the hood it creates a schema like this:

{
  type: "string",
  to: {
    type: "unknown",
  }
}

Which is not the best if you plan to use it for serializing as well. So I recommend you to add S.to after S.transform:

const a = S.string.with(S.transform, (input, s) => {
  throw s.fail('hi')
}).with(S.to, S.string)
S.safe(() => S.parseOrThrow('', a))

Which is equal to:

{
  type: "string",
  to: {
    type: "unknown",
    to: {
      type: "string",
    }
  }
}

Allowing you to use additional string refinements on the schema output + much more optimised serializing when the schema is a part of a union.

In v11 I'm working on replacing S.transform with S.to

So every time you define a transformation, you're required to pass a target schema:

const a = S.string.with(S.to, S.string, input => {
  throw new Error('hi')
})

And you'll be able to pass custom parser and serializer functions (the same as S.transform now). I'll also replace s.fail with the support of throwing normal errors.