1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152

// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// tag::description[]
//! Use to derive parsing for parsing struct.
// end::description[]

use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::quote;
use syn::parse_macro_input;

pub(crate) fn fields_idents(
	fields: impl Iterator<Item = syn::Field>,
) -> impl Iterator<Item = proc_macro2::TokenStream> {
	fields.enumerate().map(|(ix, field)| {
		field.ident.map(|i| quote! {#i}).unwrap_or_else(|| {
			let f_ix: syn::Ident = syn::Ident::new(&format!("f_{}", ix), Span::call_site());
			quote!( #f_ix )
		})
	})
}

pub(crate) fn fields_access(
	fields: impl Iterator<Item = syn::Field>,
) -> impl Iterator<Item = proc_macro2::TokenStream> {
	fields.enumerate().map(|(ix, field)| {
		field.ident.map(|i| quote!( #i )).unwrap_or_else(|| {
			let f_ix: syn::Index = syn::Index { index: ix as u32, span: Span::call_site() };
			quote!( #f_ix )
		})
	})
}

/// self defined parsing struct.
/// not meant for any struct, just for fast
/// parse implementation.
#[proc_macro_derive(Parse)]
pub fn derive_parse(input: TokenStream) -> TokenStream {
	let item = parse_macro_input!(input as syn::Item);
	match item {
		syn::Item::Struct(input) => derive_parse_struct(input),
		_ => TokenStream::new(), // ignore
	}
}

fn derive_parse_struct(input: syn::ItemStruct) -> TokenStream {
	let syn::ItemStruct { ident, generics, fields, .. } = input;
	let field_names = {
		let name = fields_idents(fields.iter().map(Clone::clone));
		quote! {
			#(
				#name,
			)*
		}
	};
	let field = fields_idents(fields.iter().map(Clone::clone));
	let tokens = quote! {
		impl #generics syn::parse::Parse for #ident #generics {
			fn parse(input: syn::parse::ParseStream) -> syn::parse::Result<Self> {
				#(
					let #field = input.parse()?;
				)*
				Ok(Self {
					#field_names
				})
			}
		}
	};
	tokens.into()
}

/// self defined parsing struct or enum.
/// not meant for any struct/enum, just for fast
/// parse implementation.
/// For enum:
///   it only output fields (empty field act as a None).
#[proc_macro_derive(ToTokens)]
pub fn derive_totokens(input: TokenStream) -> TokenStream {
	let item = parse_macro_input!(input as syn::Item);
	match item {
		syn::Item::Enum(input) => derive_totokens_enum(input),
		syn::Item::Struct(input) => derive_totokens_struct(input),
		_ => TokenStream::new(), // ignore
	}
}

fn derive_totokens_struct(input: syn::ItemStruct) -> TokenStream {
	let syn::ItemStruct { ident, generics, fields, .. } = input;

	let fields = fields_access(fields.iter().map(Clone::clone));
	let tokens = quote! {

		impl #generics quote::ToTokens for #ident #generics {
			fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
				#(
					self.#fields.to_tokens(tokens);
				)*
			}
		}

	};
	tokens.into()
}

fn derive_totokens_enum(input: syn::ItemEnum) -> TokenStream {
	let syn::ItemEnum { ident, generics, variants, .. } = input;
	let variants = variants.iter().map(|v| {
		let v_ident = v.ident.clone();
		let fields_build = if v.fields.iter().count() > 0 {
			let fields_id = fields_idents(v.fields.iter().map(Clone::clone));
			quote!( (#(#fields_id), *) )
		} else {
			quote!()
		};
		let field = fields_idents(v.fields.iter().map(Clone::clone));
		quote! {
			#ident::#v_ident #fields_build => {
				#(
					#field.to_tokens(tokens);
				)*
			},
		}
	});
	let tokens = quote! {
		impl #generics quote::ToTokens for #ident #generics {
			fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
				match self {
					#(
						#variants
					)*
				}
			}
		}
	};

	tokens.into()
}