numbat-codec-derive 0.0.3

Macro implementations of numbat-codec #[derive(NestedEncode, NestedDecode, TopEncode, TopDecode)]
Documentation 
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use crate::util::*;
use proc_macro::TokenStream;
use quote::quote;

pub fn dep_encode_snippet(value: &proc_macro2::TokenStream) -> proc_macro2::TokenStream {
	quote! {
		numbat_codec::NestedEncode::dep_encode(&#value, dest)?;
	}
}

pub fn dep_encode_or_exit_snippet(value: &proc_macro2::TokenStream) -> proc_macro2::TokenStream {
	quote! {
		numbat_codec::NestedEncode::dep_encode_or_exit(&#value, dest, c.clone(), exit);
	}
}

fn variant_dep_encode_snippets(
	name: &syn::Ident,
	data_enum: &syn::DataEnum,
) -> Vec<proc_macro2::TokenStream> {
	data_enum
		.variants
		.iter()
		.enumerate()
		.map(|(variant_index, variant)| {
			let variant_index_u8 = variant_index as u8;
			let variant_ident = &variant.ident;
			let local_var_declarations =
				fields_decl_syntax(&variant.fields, local_variable_for_field);
			let variant_field_snippets = fields_snippets(&variant.fields, |index, field| {
				dep_encode_snippet(&local_variable_for_field(index, field))
			});
			quote! {
				#name::#variant_ident #local_var_declarations => {
					numbat_codec::NestedEncode::dep_encode(&#variant_index_u8, dest)?;
					#(#variant_field_snippets)*
				},
			}
		})
		.collect()
}

fn variant_dep_encode_or_exit_snippets(
	name: &syn::Ident,
	data_enum: &syn::DataEnum,
) -> Vec<proc_macro2::TokenStream> {
	data_enum
		.variants
		.iter()
		.enumerate()
		.map(|(variant_index, variant)| {
			let variant_index_u8 = variant_index as u8;
			let variant_ident = &variant.ident;
			let local_var_declarations =
				fields_decl_syntax(&variant.fields, local_variable_for_field);
			let variant_field_snippets = fields_snippets(&variant.fields, |index, field| {
				dep_encode_or_exit_snippet(&local_variable_for_field(index, field))
			});
			quote! {
				#name::#variant_ident #local_var_declarations => {
					numbat_codec::NestedEncode::dep_encode_or_exit(&#variant_index_u8, dest, c.clone(), exit);
					#(#variant_field_snippets)*
				},
			}
		})
		.collect()
}

pub fn nested_encode_impl(ast: &syn::DeriveInput) -> TokenStream {
	let name = &ast.ident;
	let (impl_generics, ty_generics, where_clause) = &ast.generics.split_for_impl();
	let gen = match &ast.data {
		syn::Data::Struct(data_struct) => {
			let field_dep_encode_snippets = fields_snippets(&data_struct.fields, |index, field| {
				dep_encode_snippet(&self_field_expr(index, field))
			});
			let field_dep_encode_or_exit_snippets =
				fields_snippets(&data_struct.fields, |index, field| {
					dep_encode_or_exit_snippet(&self_field_expr(index, field))
				});
			quote! {
				impl #impl_generics numbat_codec::NestedEncode for #name #ty_generics #where_clause {
					fn dep_encode<O: numbat_codec::NestedEncodeOutput>(&self, dest: &mut O) -> core::result::Result<(), numbat_codec::EncodeError> {
						#(#field_dep_encode_snippets)*
						core::result::Result::Ok(())
					}

					fn dep_encode_or_exit<O: numbat_codec::NestedEncodeOutput, ExitCtx: Clone>(
						&self,
						dest: &mut O,
						c: ExitCtx,
						exit: fn(ExitCtx, numbat_codec::EncodeError) -> !,
					) {
						#(#field_dep_encode_or_exit_snippets)*
					}
				}
			}
		},
		syn::Data::Enum(data_enum) => {
			assert!(
				data_enum.variants.len() < 256,
				"enums with more than 256 variants not supported"
			);
			let variant_dep_encode_snippets = variant_dep_encode_snippets(&name, &data_enum);
			let variant_dep_encode_or_exit_snippets =
				variant_dep_encode_or_exit_snippets(&name, &data_enum);

			quote! {
				impl #impl_generics numbat_codec::NestedEncode for #name #ty_generics #where_clause {
					fn dep_encode<O: numbat_codec::NestedEncodeOutput>(&self, dest: &mut O) -> core::result::Result<(), numbat_codec::EncodeError> {
						match self {
							#(#variant_dep_encode_snippets)*
						};
						core::result::Result::Ok(())
					}

					fn dep_encode_or_exit<O: numbat_codec::NestedEncodeOutput, ExitCtx: Clone>(
						&self,
						dest: &mut O,
						c: ExitCtx,
						exit: fn(ExitCtx, numbat_codec::EncodeError) -> !,
					) {
						match self {
							#(#variant_dep_encode_or_exit_snippets)*
						};
					}
				}
			}
		},
		syn::Data::Union(_) => panic!("Union not supported"),
	};

	gen.into()
}