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    use crate::ast::{Enum, Field, Struct, Variant};
    use syn::{Member, Type};

    impl Struct<'_> {
        pub(crate) fn from_field(&self) -> Option<&Field> {
            from_field(&self.fields)
        }

        pub(crate) fn source_field(&self) -> Option<&Field> {
            source_field(&self.fields)
        }

        pub(crate) fn backtrace_field(&self) -> Option<&Field> {
            backtrace_field(&self.fields)
        }

        pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
            let backtrace_field = self.backtrace_field()?;
            distinct_backtrace_field(backtrace_field, self.from_field())
        }
    }

    impl Enum<'_> {
        pub(crate) fn has_source(&self) -> bool {
            self.variants
                .iter()
                .any(|variant| variant.source_field().is_some() || variant.attrs.transparent.is_some())
        }

        pub(crate) fn has_backtrace(&self) -> bool {
            self.variants
                .iter()
                .any(|variant| variant.backtrace_field().is_some())
        }

        pub(crate) fn has_display(&self) -> bool {
            self.attrs.display.is_some()
                || self.attrs.transparent.is_some()
                || self
                    .variants
                    .iter()
                    .any(|variant| variant.attrs.display.is_some())
                || self
                    .variants
                    .iter()
                    .all(|variant| variant.attrs.transparent.is_some())
        }
    }

    impl Variant<'_> {
        pub(crate) fn from_field(&self) -> Option<&Field> {
            from_field(&self.fields)
        }

        pub(crate) fn source_field(&self) -> Option<&Field> {
            source_field(&self.fields)
        }

        pub(crate) fn backtrace_field(&self) -> Option<&Field> {
            backtrace_field(&self.fields)
        }

        pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
            let backtrace_field = self.backtrace_field()?;
            distinct_backtrace_field(backtrace_field, self.from_field())
        }
    }

    impl Field<'_> {
        pub(crate) fn is_backtrace(&self) -> bool {
            type_is_backtrace(self.ty)
        }
    }

    fn from_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
        for field in fields {
            if field.attrs.from.is_some() {
                return Some(field);
            }
        }
        None
    }

    fn source_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
        for field in fields {
            if field.attrs.from.is_some() || field.attrs.source.is_some() {
                return Some(field);
            }
        }
        for field in fields {
            match &field.member {
                Member::Named(ident) if ident == "source" => return Some(field),
                _ => {}
            }
        }
        None
    }

    fn backtrace_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
        for field in fields {
            if field.attrs.backtrace.is_some() {
                return Some(field);
            }
        }
        for field in fields {
            if field.is_backtrace() {
                return Some(field);
            }
        }
        None
    }

    // The #[backtrace] field, if it is not the same as the #[from] field.
    fn distinct_backtrace_field<'a, 'b>(
        backtrace_field: &'a Field<'b>,
        from_field: Option<&Field>,
    ) -> Option<&'a Field<'b>> {
        if from_field.map_or(false, |from_field| {
            from_field.member == backtrace_field.member
        }) {
            None
        } else {
            Some(backtrace_field)
        }
    }

    fn type_is_backtrace(ty: &Type) -> bool {
        let path = match ty {
            Type::Path(ty) => &ty.path,
            _ => return false,
        };

        let last = path.segments.last().unwrap();
        last.ident == "Backtrace" && last.arguments.is_empty()
    }