itconfig-macro 1.1.1

Easy build a configs from environment variables and use it in globally.
Documentation 
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use proc_macro2::TokenStream as TokenStream2;
use quote::ToTokens;
use syn::{GenericArgument, Path, PathArguments, Type};

const OPTION_PATH_IDENTS: &[&str] = &["Option|", "std|option|Option|", "core|option|Option|"];
const VEC_PATH_IDENTS: &[&str] = &["Vec|", "std|vec|Vec|"];

#[derive(Debug, Clone, Default)]
pub(crate) struct VecBoxParams(Option<String>);

impl VecBoxParams {
    #[inline]
    pub(crate) fn new(sep: Option<String>) -> Self {
        VecBoxParams(sep)
    }

    #[inline]
    pub(crate) fn sep_opt(&self) -> Option<String> {
        self.0.clone()
    }

    #[inline]
    pub(crate) fn sep(&self) -> String {
        self.0.clone().unwrap_or_else(|| String::from(","))
    }
}

#[derive(Debug, Clone)]
pub(crate) enum SupportedBox {
    Vec(VecBoxParams),
    Option,
    OptionVec(VecBoxParams),
}

pub(crate) fn vec_to_token_stream_2<T>(input: &[T]) -> Vec<TokenStream2>
where
    T: ToTokens,
{
    input.iter().map(|ns| ns.into_token_stream()).collect()
}

fn path_ident(path: &Path) -> String {
    path.segments
        .iter()
        .into_iter()
        .fold(String::with_capacity(250), |mut acc, v| {
            acc.push_str(&v.ident.to_string());
            acc.push('|');
            acc
        })
}

fn is_option_path_ident(path_ident: &str) -> bool {
    OPTION_PATH_IDENTS.iter().any(|s| path_ident == *s)
}

fn is_vec_path_ident(path_ident: &str) -> bool {
    VEC_PATH_IDENTS.iter().any(|s| path_ident == *s)
}

pub(crate) fn maybe_supported_box(ty: &Type) -> Option<SupportedBox> {
    match ty {
        Type::Path(ty_path) if ty_path.qself.is_none() => {
            let ty_path_ident = path_ident(&ty_path.path);
            if is_option_path_ident(&ty_path_ident) {
                if let PathArguments::AngleBracketed(params) =
                    &ty_path.path.segments.iter().last().unwrap().arguments
                {
                    if let Some(GenericArgument::Type(Type::Path(inner_ty_path))) =
                        params.args.first()
                    {
                        let ty_path_ident = path_ident(&inner_ty_path.path);
                        if is_vec_path_ident(&ty_path_ident) {
                            return Some(SupportedBox::OptionVec(Default::default()));
                        }
                    }
                }

                Some(SupportedBox::Option)
            } else if is_vec_path_ident(&ty_path_ident) {
                Some(SupportedBox::Vec(Default::default()))
            } else {
                None
            }
        }
        _ => None,
    }
}