validators-derive 0.26.0

The provided crate offers a procedural macro for defining validators, including optional parameters.
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use std::{fmt::Display, str::FromStr};

use syn::{Expr, ExprLit, Lit, LitFloat, LitInt, Meta, UnOp};

use crate::common::path_to_string;

pub(crate) fn expr_lit_2_number<T: FromStr>(lit: &ExprLit) -> syn::Result<T>
where
    T::Err: Display, {
    match &lit.lit {
        Lit::Int(lit) => {
            return lit.base10_parse();
        },
        Lit::Float(lit) => {
            return lit.base10_parse();
        },
        _ => (),
    }

    Err(syn::Error::new_spanned(lit, "expected a number"))
}

pub(crate) fn expr_2_number<T: FromStr>(expr: &Expr) -> syn::Result<T>
where
    T::Err: Display, {
    match expr {
        Expr::Lit(lit) => return expr_lit_2_number(lit),
        Expr::Unary(unary) => {
            if let UnOp::Neg(_) = unary.op
                && let Expr::Lit(lit) = unary.expr.as_ref()
            {
                match &lit.lit {
                    Lit::Int(lit) => {
                        let s = format!("-{}", lit.base10_digits());

                        let n = <T as FromStr>::from_str(&s)
                            .map_err(|err| syn::Error::new_spanned(lit, err))?;

                        return Ok(n);
                    },
                    Lit::Float(lit) => {
                        let s = format!("-{}", lit.base10_digits());

                        let n = <T as FromStr>::from_str(&s)
                            .map_err(|err| syn::Error::new_spanned(lit, err))?;

                        return Ok(n);
                    },
                    _ => (),
                }
            }
        },
        Expr::Group(group) => {
            // should not use this, but macro rules will end up here...
            if let Expr::Lit(lit) = group.expr.as_ref() {
                return expr_lit_2_number(lit);
            }
        },
        _ => (),
    }

    Err(syn::Error::new_spanned(expr, "expected a number"))
}

#[inline]
pub(crate) fn meta_2_number<T: FromStr>(meta: &Meta) -> syn::Result<T>
where
    T::Err: Display, {
    match &meta {
        Meta::NameValue(name_value) => {
            return expr_2_number(&name_value.value);
        },
        Meta::List(list) => match list.parse_args::<LitInt>() {
            Ok(lit) => {
                return lit.base10_parse();
            },
            Err(_) => {
                let lit = list.parse_args::<LitFloat>()?;

                return lit.base10_parse();
            },
        },
        Meta::Path(_) => (),
    }

    let path = meta.path();

    Err(syn::Error::new_spanned(
        path,
        format!("expected `{path} = 0` or `{path}(0)`", path = path_to_string(path)),
    ))
}