elvis-core-support 0.1.0

Definition of the `#[elvis]` attribute, an internal dependency
Documentation 
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use syn::punctuated::Pair;
use syn::token::Colon2;
use syn::{GenericArgument, Path, PathArguments, PathSegment};

/// Extract type from option
pub fn extract_type_from_option(ty: &syn::Type) -> Option<&syn::Type> {
    fn extract_type_path(ty: &syn::Type) -> Option<&Path> {
        match *ty {
            syn::Type::Path(ref typepath) if typepath.qself.is_none() => Some(&typepath.path),
            _ => None,
        }
    }

    // TODO store (with lazy static) the vec of string
    // TODO maybe optimization, reverse the order of segments
    fn extract_option_segment(path: &Path) -> Option<Pair<&PathSegment, &Colon2>> {
        let idents_of_path = path
            .segments
            .iter()
            .into_iter()
            .fold(String::new(), |mut acc, v| {
                acc.push_str(&v.ident.to_string());
                acc.push('|');
                acc
            });

        vec!["Option|", "std|option|Option|", "core|option|Option|"]
            .into_iter()
            .find(|s| &idents_of_path == *s)
            .and_then(|_| path.segments.pairs().last())
    }

    extract_type_path(ty)
        .and_then(|path| extract_option_segment(path))
        .and_then(|pair_path_segment| {
            let type_params = &pair_path_segment.into_value().arguments;
            // It should have only on angle-bracketed param ("<String>"):
            match *type_params {
                PathArguments::AngleBracketed(ref params) => params.args.first(),
                _ => None,
            }
        })
        .and_then(|generic_arg| match *generic_arg {
            GenericArgument::Type(ref ty) => Some(ty),
            _ => None,
        })
}