vendor/strum_macros/src/macros/strings/from_string.rs

use proc_macro2::TokenStream;
use syn;

use crate::helpers::case_style::CaseStyle;
use crate::helpers::{extract_meta, CaseStyleHelpers, MetaIteratorHelpers};

pub fn from_string_inner(ast: &syn::DeriveInput) -> TokenStream {
    let name = &ast.ident;
    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
    let variants = match ast.data {
        syn::Data::Enum(ref v) => &v.variants,
        _ => panic!("FromString only works on Enums"),
    };

    let type_meta = extract_meta(&ast.attrs);
    let case_style = type_meta
        .find_unique_property("strum", "serialize_all")
        .map(|style| CaseStyle::from(style.as_ref()));

    let mut has_default = false;
    let mut default =
        quote! { _ => ::std::result::Result::Err(::strum::ParseError::VariantNotFound) };
    let mut arms = Vec::new();
    for variant in variants {
        use syn::Fields::*;
        let ident = &variant.ident;
        let meta = extract_meta(&variant.attrs);

        // Look at all the serialize attributes.
        // let mut attrs = find_properties(&meta, "strum", "serialize");
        // attrs.extend(find_properties(&meta, "strum", "to_string"));

        let mut attrs = meta.find_properties("strum", "serialize");
        attrs.extend(meta.find_properties("strum", "to_string"));

        // if is_disabled(&meta) {
        if meta.is_disabled() {
            continue;
        }

        if meta
            .find_unique_property("strum", "default")
            .map_or(false, |s| s == "true")
        {
            if has_default {
                panic!("Can't have multiple default variants");
            }

            if let Unnamed(ref fields) = variant.fields {
                if fields.unnamed.len() != 1 {
                    panic!("Default only works on unit structs with a single String parameter");
                }

                default = quote! {
                    default => ::std::result::Result::Ok(#name::#ident (default.into()))
                };
            } else {
                panic!("Default only works on unit structs with a single String parameter");
            }

            has_default = true;
            continue;
        }

        // If we don't have any custom variants, add the default serialized name.
        if attrs.len() == 0 {
            attrs.push(ident.convert_case(case_style));
        }

        let params = match variant.fields {
            Unit => quote! {},
            Unnamed(ref fields) => {
                let defaults =
                    ::std::iter::repeat(quote!(Default::default())).take(fields.unnamed.len());
                quote! { (#(#defaults),*) }
            }
            Named(ref fields) => {
                let fields = fields
                    .named
                    .iter()
                    .map(|field| field.ident.as_ref().unwrap());
                quote! { {#(#fields: Default::default()),*} }
            }
        };

        arms.push(quote! { #(#attrs)|* => ::std::result::Result::Ok(#name::#ident #params) });
    }

    arms.push(default);

    quote! {
        impl #impl_generics ::std::str::FromStr for #name #ty_generics #where_clause {
            type Err = ::strum::ParseError;
            fn from_str(s: &str) -> ::std::result::Result< #name #ty_generics , Self::Err> {
                match s {
                    #(#arms),*
                }
            }
        }
    }
}