53 lines
1.6 KiB
Rust
53 lines
1.6 KiB
Rust
use quote::quote;
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use syn::DeriveInput;
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use syn::{parse_quote, GenericParam, Generics, Result};
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pub fn derive_span(input: &DeriveInput) -> Result<impl quote::ToTokens> {
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let ty = &input.ident;
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let body = match &input.data {
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syn::Data::Struct(_) => quote! { self.span },
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syn::Data::Enum(e) => {
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let variants = e.variants.iter().map(|v| match v.fields {
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syn::Fields::Unnamed(ref fields) if fields.unnamed.len() == 1 => {
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let variant = &v.ident;
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quote! { #ty::#variant(x) => x.span(), }
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}
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_ => panic!(
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"derive(Ast) on enums only supports variants with a single, unnamed field"
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),
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});
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quote! {
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match self {
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#( #variants )*
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}
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}
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}
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syn::Data::Union(_) => {
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panic!("derive(Ast) can only be used with structs and enums, not unions")
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}
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};
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let generics = add_span_trait_bounds(input.generics.clone());
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let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
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Ok(quote! {
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impl #impl_generics Span for #ty #ty_generics #where_clause {
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#[inline]
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fn span(&self) -> wast::Span {
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#body
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}
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}
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})
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}
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// Add a bound `T: Span` to every type parameter `T`.
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fn add_span_trait_bounds(mut generics: Generics) -> Generics {
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for param in &mut generics.params {
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if let GenericParam::Type(ref mut type_param) = *param {
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type_param.bounds.push(parse_quote!(Span));
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}
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}
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generics
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}
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