feat: FromStr derive could support setting the error type

[JimChenWYU]

resolve #91 #332 #221

PR checker failed because #381

[Peternator7]

This looks really good! Sorry for the delay reviewing it

[martin-g]

Suggested change

	"`parse_err_ty` and `parse_err_fn` attribute is both required.",
	"`parse_err_ty` and `parse_err_fn` attributes are both required.",

[sebschrader]

Please reconsider using string literals for paths. Attributes nowadays support arbitrary expressions (including paths) instead of only string literals.

One of the authors of rust-analyzer recently highlighted that using string literals for such things is very bad for IDE support, in his EuroRust 2024 presentation.

[JimChenWYU]

Please reconsider using string literals for paths. Attributes nowadays support arbitrary expressions (including paths) instead of only string literals.

One of the authors of rust-analyzer recently highlighted that using string literals for such things is very bad for IDE support, in his EuroRust 2024 presentation.

@sebschrader So you want like this?

#[derive(Debug, EnumString)]
#[strum(
    parse_err_fn = crate::custom::some_enum_not_found_err,
    parse_err_ty = crate::custom::CaseCustomParseErrorNotFoundError
)]
enum CaseCustomParseErrorEnum {
    #[strum(serialize = "red")]
    Red,
    #[strum(serialize = "blue")]
    Blue,
}

mod custom {
    #[derive(Debug, Clone, Eq, PartialEq, Hash)]
    struct CaseCustomParseErrorNotFoundError(String);
    impl std::fmt::Display for CaseCustomParseErrorNotFoundError {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            writeln!(f, "not found `{}`", self.0)
        }
    }
    impl std::error::Error for CaseCustomParseErrorNotFoundError {}
    pub fn some_enum_not_found_err(s: &str) -> CaseCustomParseErrorNotFoundError {
        CaseCustomParseErrorNotFoundError(s.to_string())
    }
}

[Peternator7]

@sebschrader, I think it's a reasonable point. I've opened #410 to change this behavior since it's not released yet.