forked from Peternator7/strum
/
enum_discriminants.rs
74 lines (62 loc) · 2.46 KB
/
enum_discriminants.rs
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use proc_macro2::{Span, TokenStream};
use syn;
use helpers::{
extract_list_metas, extract_meta, filter_metas, get_meta_ident, get_meta_list, unique_meta_list,
};
pub fn enum_discriminants_inner(ast: &syn::DeriveInput) -> TokenStream {
let name = &ast.ident;
let vis = &ast.vis;
let variants = match ast.data {
syn::Data::Enum(ref v) => &v.variants,
_ => panic!("EnumDiscriminants only works on Enums"),
};
// Derives for the generated enum
let type_meta = extract_meta(&ast.attrs);
let discriminant_attrs = get_meta_list(type_meta.iter(), "strum_discriminants")
.flat_map(|meta| extract_list_metas(meta).collect::<Vec<_>>())
.collect::<Vec<&syn::Meta>>();
let derives = get_meta_list(discriminant_attrs.iter().map(|&m| m), "derive")
.flat_map(extract_list_metas)
.filter_map(get_meta_ident)
.collect::<Vec<_>>();
let derives = quote! {
#[derive(Clone, Copy, Debug, PartialEq, Eq, #(#derives),*)]
};
// Work out the name
let default_name = syn::Ident::new(
&format!("{}Discriminants", name.to_string()),
Span::call_site(),
);
let discriminants_name = unique_meta_list(discriminant_attrs.iter().map(|&m| m), "name")
.map(extract_list_metas)
.and_then(|metas| metas.filter_map(get_meta_ident).next())
.unwrap_or(&default_name);
// Pass through all other attributes
let pass_though_attributes =
filter_metas(discriminant_attrs.iter().map(|&m| m), |meta| match meta {
syn::Meta::List(ref metalist) => metalist.ident != "derive" && metalist.ident != "name",
_ => true,
}).map(|meta| quote! { #[ #meta ] })
.collect::<Vec<_>>();
// Add the variants without fields, but exclude the `strum` meta item
let mut discriminants = Vec::new();
for variant in variants {
let ident = &variant.ident;
// Don't copy across the "strum" meta attribute.
let attrs = variant.attrs.iter().filter(|attr| {
attr.interpret_meta().map_or(true, |meta| match meta {
syn::Meta::List(ref metalist) => metalist.ident != "strum",
_ => true,
})
});
discriminants.push(quote!{ #(#attrs)* #ident });
}
quote!{
/// Auto-generated discriminant enum variants
#derives
#(#pass_though_attributes)*
#vis enum #discriminants_name {
#(#discriminants),*
}
}
}