Object schema breaking nested pipe output type

[buzlo]

Hey again, I've noticed a weird behavior with the latest update.

Here is an example snippet of transform pipe nested inside an object schema.

const transformPipe = pipe(optional(string()), transform((input) => input ?? 'fallback'))
const objectSchema = object({
	pipeField: transformPipe,
	noPipeField: string(),
})

type PipeOutputType = InferOutput<typeof transformPipe> // string
type ObjectOutputType = InferOutput<(typeof objectSchema)> //  { pipeField?: string | undefined;  noPipeField: string; }

As you can see, the output type of that pipe is clearly string, but when it is nested inside an object schema it is still for some reason inferred as optional, while the type of a field that is directly assigned string() schema is inferred correctly.

This is most likely a bug, could you please look into it?
Thanks!

[fabian-hiller]

Thank you for reaching out! This is not a bug. We expanded the validation capabilities of object to be able to distinguish between undefined properties and missing properties. I recommend to change your code to:

const Schema = v.optional(v.string(), 'default');

Feel free to reach out with any question you have. I am happy to explain what's happening under the hood.

[buzlo]

May I ask you to elaborate?
This behavior still seems kind of unexpected to me: the input for transformPipe is indeed optional(string), which can be undefined or missing, but the output is strictly string.
The output could also theoretically be another completely unrelated, non-nullish type, the result of some internal transform logic from a string/undefined/missing field to whatever new type that might be.
The point is: even if the input for this transform action might be undefined or missing, its output is certainly not, that's why it doesn't seem right to me.
Could you please explain? Thanks!

[fabian-hiller]

Yes, I can explain it. optional signals to object that it is ok if the property is missing. If this is the case, as we distinguish between missing and undefined properties, the schema of the property is not executed. We chose to implement it this way because there are drawbacks in a few edge cases when we would execute the schema of the property. But by providing a default value (the second argument of optional), you tell object to execute the schema and apply the default value. There is a blog post a GitHub discussion and few PRs with more context.

[throrin19]

I don't know if my problem is the same but I try to migrate to 1.0.0 and I have a problem with nullish in object field.

Before 1.0.0 if I made this :

const schema = object({
    a: nullish(string(), 'default'),
});

const result = parse(schema, {}}, {
            abortEarly: true,
            abortPipeEarly: true,
        });

// { a: 'default'}

After 1.0.0 I have an error :

const schema = object({
    a: nullish(string(), 'default'),
});

const result = parse(schema, {}}, {
            abortEarly: true,
            abortPipeEarly: true,
        });

// Invalid key: Expected \\"a\\" but received undefined

[fabian-hiller]

@throrin19 it should work. See this playground: https://valibot.dev/playground/?code=JYWwDg9gTgLgBAKjgQwM5wG5wGZQiOAcg2QBtgAjCGQgbgCh6BjCAO1XlSYAsBTEZHAC8mAHQQKAK15MYACgDe9OCgBcY1gFdS5VNzkZRHKMFYBzOQEoANEQAmvbMm00b9AL6WGzNhzhReVBdhMTBkKFReOWU4Lj4BaxiFd0SVJRUVZCpYAFFw0gBPdRgoTV5UjKzoGAAFYDBePKhC4tLymJT6L0YWdghSXlFSCAsAoNIYbqA