vouched

vouched provides a derive macro for tuple-struct newtypes whose values are vouched for after validation.

Install

[dependencies]
vouched = "0.3"

Quick start

use vouched::Vouched;

#[derive(Debug, PartialEq, Eq, Vouched)]
#[vouched(len(1..=64), chars('a'..='z', '0'..='9', '_'), impls(try_from(&str)))]
struct Slug(String);
impl Slug {
    fn as_str(&self) -> &str {
        &self.0
    }
}

let slug = Slug::try_from("hello_123")?;
assert_eq!(slug.as_str(), "hello_123");

Examples

See crates/vouched/examples for more detailed, executable examples.

cargo run -p vouched --example <name>

Supported Markers

• len(range): validates string length by Unicode scalar value count. Leading and trailing whitespace count.
• range(range): validates numeric bounds for i8, i16, i32, i64, i128, u8, u16, u32, u64, u128, f32, and f64.
• chars(...): validates allowed characters by string literal, char literal, or inclusive char range.

len(...), range(...), and chars(...) can each be specified at most once. To combine character sets, put all sources in one marker, such as chars('a'..='z', '0'..='9', '_').

range(...) type-checks the bound expressions against the inner numeric type and generates runtime validation. Float ranges reject an actual NaN value as not comparable. Float bound expressions must not evaluate to NaN; Rust float comparison rules make a NaN bound ineffective. range(...) does not guarantee the range is non-empty; for example, a contradictory range remains the user's constraint.

Validation returns the first error encountered. When multiple markers or multiple constraints fail, the exact evaluation order is an implementation detail. The implementation may move expensive whole-string validations later to reduce validation cost.

Generated API

#[derive(Vouched)] generates TryFrom impls, a <TypeName>VouchedError enum, Display, core::error::Error, and vouched::VouchedError. Use impls(try_from(...)) to request additional TryFrom implementations before validation. Supported sources are fallible fixed-width integer conversions and &str for string validation newtypes with supported owned string inner types: String, Box<str>, Rc<str>, and Arc<str>. For impls(try_from(&str)), the generated implementation validates the borrowed input before constructing the inner value, so invalid inputs do not allocate. Custom string wrapper inner types are not supported by this impl. The default error enum visibility matches the derived type visibility. Use #[vouched(error(name = CustomErrorName, vis = pub(crate)), ...)] to override the generated error enum name or visibility. Rust visibility rules still apply: if a public derived type exposes a less-visible error type through TryFrom::Error, rustc rejects the generated impl.

Feature flags

features	crate mode	available
default / std	std	derive macro, core errors, generated errors, erased Error
alloc without default	no_std + alloc	derive macro, core errors, generated errors, erased Error
no default features	no_std	derive macro, core errors, generated errors; no erased Error
valuable	no_std + alloc	all alloc items plus valuable::Valuable impls for structured error observation

std enables alloc. valuable also enables alloc.

Limitations

• Only tuple structs with exactly one field are supported.
• The default generated error enum name is <TypeName>VouchedError; use error(name = CustomErrorName) to avoid local name collisions.
• Integer impls(try_from(...)) supports only fallible fixed-width conversions among i8, i16, i32, i64, i128, u8, u16, u32, u64, and u128.
• impls(try_from(&str)) supports only len(...) and/or chars(...), cannot be mixed with integer sources, and requires String, Box<str>, Rc<str>, or Arc<str> as the inner type. Custom string wrapper inners and borrowed inners that store the input lifetime are not supported.
• range(...) supports fixed-width integers plus f32 and f64; isize, usize, and custom ordered types are not supported.
• len(...) works on AsRef<str> values and measures untrimmed Unicode scalar values, not bytes.
• chars(...) works on AsRef<str> values and validates untrimmed Unicode scalar values.

Versioning

While vouched is in 0.x, breaking changes to public APIs, generated APIs, or documented behavior require a minor version bump. Patch releases are limited to bug fixes, documentation updates, and non-breaking additions.

The current MSRV is Rust 1.86. MSRV changes are not shipped in patch releases; while vouched is in 0.x, an MSRV bump is treated as a possibly-breaking compatibility change and shipped in a minor release with release notes.

After 1.0.0, vouched follows SemVer for public APIs and documented behavior.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.