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use serde::{Deserialize, Deserializer};

#[derive(Debug, PartialEq, Eq)]
pub struct True;

impl<'de> Deserialize<'de> for True {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let bool = bool::deserialize(deserializer)?;

        if bool {
            Ok(True)
        } else {
            Err(serde::de::Error::invalid_value(
                serde::de::Unexpected::Bool(false),
                &"the `true` boolean",
            ))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[derive(Debug, Deserialize, PartialEq)]
    struct Foo {
        foo: True,
    }

    #[test]
    fn de_true() {
        assert_eq!(
            Foo { foo: True },
            serde_json::from_str::<Foo>(r#"{"foo": true}"#).unwrap(),
        );

        serde_json::from_str::<Foo>(r#"{"foo": false}"#).unwrap_err();
    }
}