numbat-codec-derive 0.0.3

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

use crate::util::*;

pub fn dep_decode_snippet(_index: usize, field: &syn::Field) -> proc_macro2::TokenStream {
	let ty = &field.ty;
	if let Some(ident) = &field.ident {
		quote! {
			#ident: <#ty as numbat_codec::NestedDecode>::dep_decode(input)?
		}
	} else {
		quote! {
			<#ty as numbat_codec::NestedDecode>::dep_decode(input)?
		}
	}
}

pub fn dep_decode_or_exit_snippet(_index: usize, field: &syn::Field) -> proc_macro2::TokenStream {
	let ty = &field.ty;
	if let Some(ident) = &field.ident {
		quote! {
			#ident: <#ty as numbat_codec::NestedDecode>::dep_decode_or_exit(input, c.clone(), exit)
		}
	} else {
		quote! {
			<#ty as numbat_codec::NestedDecode>::dep_decode_or_exit(input, c.clone(), exit)
		}
	}
}

pub fn variant_dep_decode_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 variant_field_snippets = fields_decl_syntax(&variant.fields, |index, field| {
				dep_decode_snippet(index, field)
			});
			quote! {
				#variant_index_u8 => core::result::Result::Ok( #name::#variant_ident #variant_field_snippets ),
			}
		})
		.collect()
}

pub fn variant_dep_decode_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 variant_field_snippets = fields_decl_syntax(&variant.fields, |index, field| {
				dep_decode_or_exit_snippet(index, field)
			});
			quote! {
				#variant_index_u8 => #name::#variant_ident #variant_field_snippets ,
			}
		})
		.collect()
}

pub fn nested_decode_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_decode_snippets =
				fields_decl_syntax(&data_struct.fields, |index, field| {
					dep_decode_snippet(index, field)
				});
			let field_dep_encode_or_exit_snippets =
				fields_decl_syntax(&data_struct.fields, |index, field| {
					dep_decode_or_exit_snippet(index, field)
				});
			quote! {
				impl #impl_generics numbat_codec::NestedDecode for #name #ty_generics #where_clause {
					fn dep_decode<I: numbat_codec::NestedDecodeInput>(input: &mut I) -> core::result::Result<Self, numbat_codec::DecodeError> {
						core::result::Result::Ok(
							#name #field_dep_decode_snippets
						)
					}

					fn dep_decode_or_exit<I: numbat_codec::NestedDecodeInput, ExitCtx: Clone>(
						input: &mut I,
						c: ExitCtx,
						exit: fn(ExitCtx, numbat_codec::DecodeError) -> !,
					) -> Self {
						#name #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_decode_snippets = variant_dep_decode_snippets(&name, &data_enum);
			let variant_dep_decode_or_exit_snippets =
				variant_dep_decode_or_exit_snippets(&name, &data_enum);

			quote! {
				impl #impl_generics numbat_codec::NestedDecode for #name #ty_generics #where_clause {
					fn dep_decode<I: numbat_codec::NestedDecodeInput>(input: &mut I) -> core::result::Result<Self, numbat_codec::DecodeError> {
						match <u8 as numbat_codec::NestedDecode>::dep_decode(input)? {
							#(#variant_dep_decode_snippets)*
							_ => core::result::Result::Err(numbat_codec::DecodeError::INVALID_VALUE),
						}
					}

					fn dep_decode_or_exit<I: numbat_codec::NestedDecodeInput, ExitCtx: Clone>(
						input: &mut I,
						c: ExitCtx,
						exit: fn(ExitCtx, numbat_codec::DecodeError) -> !,
					) -> Self {
						match <u8 as numbat_codec::NestedDecode>::dep_decode_or_exit(input, c.clone(), exit) {
							#(#variant_dep_decode_or_exit_snippets)*
							_ => exit(c, numbat_codec::DecodeError::INVALID_VALUE),
						}
					}
				}
			}
		},
		syn::Data::Union(_) => panic!("Union not supported"),
	};

	gen.into()
}