serde_string_or_u32.rs

use std::str::FromStr;
use std::marker::PhantomData;
use serde::de::{self, Visitor};

pub struct StringOrU32Visitor<T> {
    marker: PhantomData<T>,
}

impl<T> StringOrU32Visitor<T> {
    pub fn new() -> Self {
        Self {
            marker: PhantomData,
        }
    }
}

impl<'de, T> Visitor<'de> for StringOrU32Visitor<T>
where
    T: TryFrom<u32> + std::str::FromStr,
    <T as FromStr>::Err: std::fmt::Display,
    <T as TryFrom<u32>>::Error: std::fmt::Display,
{
    type Value = T;
    
    fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
        formatter.write_str("a string or integer")
    }
    
    fn visit_u64<E>(self, value: u64) -> Result<Self::Value, E>
    where
        E: de::Error,
    {
        let value = u32::try_from(value)
            .map_err(|_| serde::de::Error::invalid_value(de::Unexpected::Unsigned(value), &self))?;
        
        T::try_from(value)
            .map_err(|e| serde::de::Error::custom(e.to_string()))
    }
    
    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
    where
        E: de::Error,
    {
        T::from_str(s)
            .map_err(|e| serde::de::Error::custom(e.to_string()))
    }
}