teleparse-macros 0.1.0

Proc-macro crate for teleparse
Documentation 
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use crate::*;

pub fn expand(input: &syn::DeriveInput) -> syn::Result<TokenStream2> {
    let teleparse = crate_ident();
    let ident = &input.ident;
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let (lo_body, hi_body) = match &input.data {
        syn::Data::Union(_) => {
            syn_error!(input, "Union is not supported for ToSpan");
        }
        syn::Data::Enum(data) => (
            expand_enum(data, quote! { lo() })?,
            expand_enum(data, quote! { hi() })?,
        ),
        syn::Data::Struct(data) => (
            expand_struct(data, quote! { lo() })?,
            expand_struct(data, quote! { hi() })?,
        ),
    };

    let out = quote! {
        #[automatically_derived]
        impl #impl_generics #teleparse::ToSpan for #ident #ty_generics #where_clause {
            fn lo(&self) -> #teleparse::Pos {
                #lo_body
            }
            fn hi(&self) -> #teleparse::Pos {
                #hi_body
            }
        }
    };

    Ok(out)
}

fn expand_struct(input: &syn::DataStruct, expr: TokenStream2) -> syn::Result<TokenStream2> {
    let teleparse = crate_ident();
    match &input.fields {
        syn::Fields::Named(fields) => {
            let ident = match fields.named.first() {
                Some(syn::Field {
                    ident: Some(id), ..
                }) => id,
                _ => {
                    return unsupported_empty_field(&input.fields);
                }
            };
            Ok(quote! {
                use #teleparse::ToSpan;
                self.#ident.#expr
            })
        }
        syn::Fields::Unnamed(_) => Ok(quote! {
            use #teleparse::ToSpan;
            self.0.#expr
        }),
        syn::Fields::Unit => unsupported_empty_field(&input.fields),
    }
}

fn expand_enum(input: &syn::DataEnum, expr: TokenStream2) -> syn::Result<TokenStream2> {
    let teleparse = crate_ident();
    let mut arms = TokenStream2::new();
    for variant in &input.variants {
        let ident = &variant.ident;
        match &variant.fields {
            syn::Fields::Named(fields) => {
                let field = match fields.named.first() {
                    Some(syn::Field {
                        ident: Some(id), ..
                    }) => id,
                    _ => {
                        return unsupported_empty_field(&variant.fields);
                    }
                };
                arms.extend(quote! {
                    Self::#ident { #field, .. } => #field.#expr,
                });
            }
            syn::Fields::Unnamed(_) => {
                arms.extend(quote! {
                    Self::#ident(x, ..) => x.#expr,
                });
            }
            syn::Fields::Unit => {
                unsupported_empty_field(&variant.fields)?;
            }
        }
    }

    Ok(quote! {
        use #teleparse::ToSpan;
        match self {
            #arms
        }
    })
}

fn unsupported_empty_field(fields: &syn::Fields) -> syn::Result<TokenStream2> {
    syn_error!(fields, "Must have at least one field to derive ToSpan");
}