Validators

A validator assesses (and may transform) a field's value. Lax, required and virtual fields can each have up to two: a primary #[validate] and a secondary #[re_validate], which only runs once the primary validator has already succeeded.

Both share the same signature: |value, ctx, opts| -> Result<Option<T>, (String, Option<Metadata>)>.

• Ok(None) accepts the value as-is.
• Ok(Some(new_value)) replaces it.
• Err((reason, metadata)) rejects it -- metadata is None unless you're using a custom IvoErrorSanitizer.

use ivo::ivo_schema;

#[ivo_schema(input(DataInput, derive(Debug, Clone, PartialEq)))]
mod re_validate_schema {
    struct Fields {
        #[required]
        #[validate(|v: String, _, _| Ok(Some(v)))]
        #[re_validate(|v: String, _, _| Ok(Some(format!("revalidated-{v}"))))]
        pub username: String,
    }
}

fn main() {
    let created = re_validate_schema::DataInputModel
        .create(
            re_validate_schema::PartialDataInput {
                username: Some("jane".into()),
            },
            (),
        )
        .unwrap();

    println!("{:?}", created.data); // DataInput { username: "revalidated-jane" }
}

#[re_validate] requires #[validate] to be present on the same field -- it's a compile error otherwise. See it used for real (checking a username isn't already taken, via ctx_options) in examples/main_demo.

• Validators & re-validators: see lax fields, required fields and virtual fields
• Custom required errors: see Required Fields

Built-in validation helpers

Enable the optional validators feature (ivo = { version = "*", features = ["validators"] }, crate ivo-validators) for a small set of built-in validators:

• validate_email(value: &str) -> Result<String, String>
• validate_credit_card(value: &str) -> Result<String, String>

#[lax(None)]
#[validate(|v: Option<String>, _, _| {
    let Some(email) = v else { return Ok(None) };
    match validate_email(&email) {
        Ok(validated) => Ok(Some(Some(validated))),
        Err(e) => Err((e, None)),
    }
})]
pub email: Option<String>,

See the crate source for implementation details, and main_demo for a schema that uses them.