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extern crate proc_macro;
extern crate proc_macro2;
#[macro_use]
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro2::{Ident, Span, TokenStream};
use syn::DeriveInput;
fn unit_fields_return(
name: &syn::Ident,
variant_name: &syn::Ident,
function_name: &Ident,
) -> TokenStream {
quote!(
impl #name {
pub fn #function_name(&self) -> Option<isize> {
match self {
#name::#variant_name => {
Some(#name::#variant_name as isize)
}
_ => None
}
}
}
)
}
fn unnamed_fields_return(
name: &syn::Ident,
variant_name: &syn::Ident,
function_name: &Ident,
fields: &syn::FieldsUnnamed,
) -> TokenStream {
let (returns, matches, accesses) = match fields.unnamed.len() {
1 => {
let field = fields.unnamed.first().expect("no fields on type");
let field = field.value();
let returns = &field.ty;
let returns = quote!(&#returns);
let matches = quote!(inner);
let accesses = quote!(&inner);
(returns, matches, accesses)
}
0 => (quote!(()), quote!(), quote!(())),
_ => {
let mut returns = TokenStream::new();
let mut matches = TokenStream::new();
let mut accesses = TokenStream::new();
for (i, field) in fields.unnamed.iter().enumerate() {
let rt = &field.ty;
let match_name = Ident::new(&format!("match_{}", i), Span::call_site());
returns.extend(quote!(&#rt,));
matches.extend(quote!(#match_name,));
accesses.extend(quote!(&#match_name,));
}
(quote!((#returns)), quote!(#matches), quote!((#accesses)))
}
};
quote!(
impl #name {
pub fn #function_name(&self) -> Option<#returns> {
match self {
#name::#variant_name(#matches) => {
Some(#accesses)
}
_ => None
}
}
}
)
}
fn named_fields_return(
name: &syn::Ident,
variant_name: &syn::Ident,
function_name: &Ident,
fields: &syn::FieldsNamed,
) -> TokenStream {
let (returns, matches, accesses) = match fields.named.len() {
1 => {
let field = fields.named.first().expect("no fields on type");
let field = field.value();
let match_name = field.ident.as_ref().expect("expected a named field");
let returns = &field.ty;
let returns = quote!(&#returns);
let matches = quote!(#match_name);
let accesses = quote!(&#match_name);
(returns, matches, accesses)
}
0 => (quote!(()), quote!(), quote!(())),
_ => {
let mut returns = TokenStream::new();
let mut matches = TokenStream::new();
let mut accesses = TokenStream::new();
for field in fields.named.iter() {
let rt = &field.ty;
let match_name = field.ident.as_ref().expect("expected a named field");
returns.extend(quote!(&#rt,));
matches.extend(quote!(#match_name,));
accesses.extend(quote!(&#match_name,));
}
(quote!((#returns)), quote!(#matches), quote!((#accesses)))
}
};
quote!(
impl #name {
pub fn #function_name(&self) -> Option<#returns> {
match self {
#name::#variant_name{ #matches } => {
Some(#accesses)
}
_ => None
}
}
}
)
}
fn impl_all_as_fns(ast: &DeriveInput) -> TokenStream {
let name = &ast.ident;
let enum_data = if let syn::Data::Enum(data) = &ast.data {
data
} else {
panic!("{} is not an enum", name);
};
let mut stream = TokenStream::new();
for variant_data in &enum_data.variants {
let variant_name = &variant_data.ident;
let function_name = Ident::new(
&format!("as_{}", variant_name).to_lowercase(),
Span::call_site(),
);
let tokens = match &variant_data.fields {
syn::Fields::Unit => unit_fields_return(name, variant_name, &function_name),
syn::Fields::Unnamed(unnamed) => {
unnamed_fields_return(name, variant_name, &function_name, &unnamed)
}
syn::Fields::Named(named) => {
named_fields_return(name, variant_name, &function_name, &named)
}
};
stream.extend(tokens);
}
stream
}
#[proc_macro_derive(EnumAsInner)]
pub fn enum_as_inner(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let ast: DeriveInput = parse_macro_input!(input as DeriveInput);
let expanded: TokenStream = impl_all_as_fns(&ast);
proc_macro::TokenStream::from(expanded)
}