80 lines
2.1 KiB
Rust
80 lines
2.1 KiB
Rust
use proc_macro::TokenStream;
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use quote::quote;
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use syn::DeriveInput;
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use syn::__private::TokenStream2;
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pub fn action(input: TokenStream) -> TokenStream {
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let input = syn::parse::<DeriveInput>(input).unwrap();
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let name = &input.ident;
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let enum_data = if let syn::Data::Enum(enum_data) = &input.data {
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enum_data
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} else {
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panic!("`Register` can only be used on enums");
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};
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let variant_description = generate_variant_description(enum_data);
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let variant_constants = generate_variant_constants(name, enum_data);
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let expanded = compile_output(name, variant_description, variant_constants);
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TokenStream::from(expanded)
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}
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fn generate_variant_description(
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enum_data: &syn::DataEnum,
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) -> impl Iterator<Item = TokenStream2> + '_ {
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let variant_matches_backend = enum_data.variants.iter().map(|variant| {
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let variant_name = &variant.ident;
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let variant_lowercase =
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proc_macro2::Literal::string(&variant_name.to_string().to_lowercase());
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quote! {
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Self::#variant_name => #variant_lowercase,
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}
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});
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variant_matches_backend
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}
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fn generate_variant_constants<'a>(
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name: &'a syn::Ident,
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enum_data: &'a syn::DataEnum,
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) -> impl Iterator<Item = TokenStream2> + 'a {
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let result = enum_data.variants.iter().map(move |variant| {
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let variant_name = &variant.ident;
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let variant_uppercase = proc_macro2::Ident::new(
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&variant_name.to_string().to_uppercase(),
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proc_macro2::Span::call_site(),
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);
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quote! {
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pub(crate) const #variant_uppercase: &str = #name::#variant_name.name();
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}
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});
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result
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}
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fn compile_output<T, U>(
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name: &syn::Ident,
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variant_description: T,
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variant_constants: U,
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) -> TokenStream2
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where
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T: Iterator<Item = TokenStream2>,
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U: Iterator<Item = TokenStream2>,
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{
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let expanded = quote! {
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impl #name {
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pub const fn name(&self) -> &'static str {
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match self {
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#(#variant_description)*
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}
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}
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}
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#(#variant_constants)*
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};
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expanded
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}
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