1 use proc_macro2::{Span, TokenTree};
2 use syn::parse::{Error, Parse, ParseStream, Result};
3 use syn::{token, Attribute, Data, DeriveInput, Expr, Fields, Ident, Meta, Token};
8 pub variants: Vec<Variant>,
9 pub default_variant: Option<Variant>,
15 pub attrs: VariantAttrs,
19 pub struct VariantAttrs {
23 fn parse_serde_attr(attrs: &mut VariantAttrs, attr: &Attribute) {
24 if let Meta::List(_) = attr.meta {
25 let _ = attr.parse_nested_meta(|meta| {
26 if meta.input.peek(Token![=]) {
27 let _value: Expr = meta.value()?.parse()?;
28 } else if meta.input.peek(token::Paren) {
29 let _group: TokenTree = meta.input.parse()?;
30 } else if meta.path.is_ident("other") {
31 attrs.is_default = true;
38 fn parse_attrs(variant: &syn::Variant) -> VariantAttrs {
39 let mut attrs = VariantAttrs { is_default: false };
40 for attr in &variant.attrs {
41 if attr.path().is_ident("serde") {
42 parse_serde_attr(&mut attrs, attr);
48 impl Parse for Input {
49 fn parse(input: ParseStream) -> Result<Self> {
50 let call_site = Span::call_site();
51 let derive_input = DeriveInput::parse(input)?;
53 let data = match derive_input.data {
54 Data::Enum(data) => data,
56 return Err(Error::new(call_site, "input must be an enum"));
63 .map(|variant| match variant.fields {
65 let attrs = parse_attrs(&variant);
71 Fields::Named(_) | Fields::Unnamed(_) => {
72 Err(Error::new(variant.ident.span(), "must be a unit variant"))
75 .collect::<Result<Vec<Variant>>>()?;
77 if variants.is_empty() {
78 return Err(Error::new(call_site, "there must be at least one variant"));
81 let generics = derive_input.generics;
82 if !generics.params.is_empty() || generics.where_clause.is_some() {
83 return Err(Error::new(call_site, "generic enum is not supported"));
87 for attr in derive_input.attrs {
88 if attr.path().is_ident("repr") {
89 if let Meta::List(_) = &attr.meta {
90 let ty: Ident = attr.parse_args()?;
96 let repr = repr.ok_or_else(|| Error::new(call_site, "missing #[repr(...)] attribute"))?;
98 let mut default_variants = variants.iter().filter(|x| x.attrs.is_default);
99 let default_variant = default_variants.next().cloned();
100 if default_variants.next().is_some() {
101 return Err(Error::new(
103 "only one variant can be #[serde(other)]",
108 ident: derive_input.ident,