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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
// Copyright 2017-2018 Parity Technologies
//
// 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.

//! Derives serialization and deserialization codec for complex structs for simple marshalling.

#![recursion_limit = "128"]
extern crate proc_macro;

#[macro_use]
extern crate syn;

#[macro_use]
extern crate quote;

use proc_macro2::{Ident, Span};
use proc_macro_crate::crate_name;
use syn::spanned::Spanned;
use syn::{Data, Field, Fields, DeriveInput, Error};

mod decode;
mod encode;
mod utils;
mod trait_bounds;

/// Include the `parity-scale-codec` crate under a known name (`_parity_scale_codec`).
fn include_parity_scale_codec_crate() -> proc_macro2::TokenStream {
	// This "hack" is required for the tests.
	if std::env::var("CARGO_PKG_NAME").unwrap() == "parity-scale-codec" {
		quote!( extern crate parity_scale_codec as _parity_scale_codec; )
	} else {
		match crate_name("parity-scale-codec") {
			Ok(parity_codec_crate) => {
				let ident = Ident::new(&parity_codec_crate, Span::call_site());
				quote!( extern crate #ident as _parity_scale_codec; )
			},
			Err(e) => Error::new(Span::call_site(), &e).to_compile_error(),
		}
	}
}

/// Wraps the impl block in a "dummy const"
fn wrap_with_dummy_const(impl_block: proc_macro2::TokenStream) -> proc_macro::TokenStream {
	let parity_codec_crate = include_parity_scale_codec_crate();

	let generated = quote! {
		const _: () = {
			#[allow(unknown_lints)]
			#[cfg_attr(feature = "cargo-clippy", allow(useless_attribute))]
			#[allow(rust_2018_idioms)]
			#parity_codec_crate
			#impl_block
		};
	};

	generated.into()
}

/// Derive `parity_scale_codec::Encode` and `parity_scale_codec::EncodeLike` for struct and enum.
///
/// # Struct
///
/// A struct is encoded by encoding each of its fields successively.
///
/// Fields can have some attributes:
/// * `#[codec(skip)]`: the field is not encoded. It must derive `Default` if Decode is derived.
/// * `#[codec(compact)]`: the field is encoded in its compact representation i.e. the field must
///   implement `parity_scale_codec::HasCompact` and will be encoded as `HasCompact::Type`.
/// * `#[codec(encoded_as = "$EncodeAs")]`: the field is encoded as an alternative type. $EncodedAs
///   type must implement `parity_scale_codec::EncodeAsRef<'_, $FieldType>` with $FieldType the
///   type of the field with the attribute. This is intended to be used for types implementing
///   `HasCompact` as shown in the example.
///
/// ```
/// # use parity_scale_codec_derive::Encode;
/// # use parity_scale_codec::{Encode as _, HasCompact};
/// #[derive(Encode)]
/// struct StructType {
///		#[codec(skip)]
///		a: u32,
///		#[codec(compact)]
/// 	b: u32,
///		#[codec(encoded_as = "<u32 as HasCompact>::Type")]
///		c: u32,
/// }
/// ```
///
/// # Enum
///
/// The variable is encoded with one byte for the variant and then the variant struct encoding.
/// The variant number is:
/// * if variant has attribute: `#[codec(index = "$n")]` then n
/// * else if variant has discrimant (like 3 in `enum T { A = 3 }`) then the discrimant.
/// * else its position in the variant set, excluding skipped variants, but including variant with
/// discrimant or attribute. Warning this position does collision with discrimant or attribute
/// index.
///
/// variant attributes:
/// * `#[codec(skip)]`: the variant is not encoded.
/// * `#[codec(index = "$n")]`: override variant index.
///
/// field attributes: same as struct fields attributes.
///
/// ```
/// # use parity_scale_codec_derive::Encode;
/// # use parity_scale_codec::Encode as _;
/// #[derive(Encode)]
/// enum EnumType {
/// 	#[codec(index = "15")]
/// 	A,
/// 	#[codec(skip)]
/// 	B,
/// 	C = 3,
/// 	D,
/// }
///
/// assert_eq!(EnumType::A.encode(), vec![15]);
/// assert_eq!(EnumType::B.encode(), vec![]);
/// assert_eq!(EnumType::C.encode(), vec![3]);
/// assert_eq!(EnumType::D.encode(), vec![2]);
/// ```
#[proc_macro_derive(Encode, attributes(codec))]
pub fn encode_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
	let mut input: DeriveInput = match syn::parse(input) {
		Ok(input) => input,
		Err(e) => return e.to_compile_error().into(),
	};
	if let Some(span) = utils::get_skip(&input.attrs) {
		return Error::new(span, "invalid attribute `skip` on root input")
			.to_compile_error().into();
	}

	if let Err(e) = trait_bounds::add(
		&input.ident,
		&mut input.generics,
		&input.data,
		parse_quote!(_parity_scale_codec::Encode),
		None,
		utils::get_dumb_trait_bound(&input.attrs),
	) {
		return e.to_compile_error().into();
	}

	let name = &input.ident;
	let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

	let encode_impl = encode::quote(&input.data, name);

	let impl_block = quote! {
		impl #impl_generics _parity_scale_codec::Encode for #name #ty_generics #where_clause {
			#encode_impl
		}

		impl #impl_generics _parity_scale_codec::EncodeLike for #name #ty_generics #where_clause {}
	};

	wrap_with_dummy_const(impl_block)
}

/// Derive `parity_scale_codec::Decode` and for struct and enum.
///
/// see derive `Encode` documentation.
#[proc_macro_derive(Decode, attributes(codec))]
pub fn decode_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
	let mut input: DeriveInput = match syn::parse(input) {
		Ok(input) => input,
		Err(e) => return e.to_compile_error().into(),
	};
	if let Some(span) = utils::get_skip(&input.attrs) {
		return Error::new(span, "invalid attribute `skip` on root input")
			.to_compile_error().into();
	}

	if let Err(e) = trait_bounds::add(
		&input.ident,
		&mut input.generics,
		&input.data,
		parse_quote!(_parity_scale_codec::Decode),
		Some(parse_quote!(Default)),
		utils::get_dumb_trait_bound(&input.attrs),
	) {
		return e.to_compile_error().into();
	}

	let name = &input.ident;
	let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

	let input_ = quote!(__codec_input_edqy);
	let decoding = decode::quote(&input.data, name, &input_);

	let impl_block = quote! {
		impl #impl_generics _parity_scale_codec::Decode for #name #ty_generics #where_clause {
			fn decode<__CodecInputEdqy: _parity_scale_codec::Input>(
				#input_: &mut __CodecInputEdqy
			) -> core::result::Result<Self, _parity_scale_codec::Error> {
				#decoding
			}
		}
	};

	wrap_with_dummy_const(impl_block)
}

/// Derive `parity_scale_codec::Compact` and `parity_scale_codec::CompactAs` for struct with single
/// field.
///
/// Attribute skip can be used to skip other fields.
///
/// # Example
///
/// ```
/// # use parity_scale_codec_derive::CompactAs;
/// # use parity_scale_codec::{Encode, HasCompact};
/// # use std::marker::PhantomData;
/// #[derive(CompactAs)]
/// struct MyWrapper<T>(u32, #[codec(skip)] PhantomData<T>);
/// ```
#[proc_macro_derive(CompactAs, attributes(codec))]
pub fn compact_as_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
	let mut input: DeriveInput = match syn::parse(input) {
		Ok(input) => input,
		Err(e) => return e.to_compile_error().into(),
	};

	if let Err(e) = trait_bounds::add(
		&input.ident,
		&mut input.generics,
		&input.data,
		parse_quote!(_parity_scale_codec::CompactAs),
		None,
		utils::get_dumb_trait_bound(&input.attrs),
	) {
		return e.to_compile_error().into();
	}

	let name = &input.ident;
	let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

	fn val_or_default(field: &Field) -> proc_macro2::TokenStream {
		let skip = utils::get_skip(&field.attrs).is_some();
		if skip {
			quote_spanned!(field.span()=> Default::default())
		} else {
			quote_spanned!(field.span()=> x)
		}
	}

	let (inner_ty, inner_field, constructor) = match input.data {
		Data::Struct(ref data) => {
			match data.fields {
				Fields::Named(ref fields) if utils::filter_skip_named(fields).count() == 1 => {
					let recurse = fields.named.iter().map(|f| {
						let name_ident = &f.ident;
						let val_or_default = val_or_default(&f);
						quote_spanned!(f.span()=> #name_ident: #val_or_default)
					});
					let field = utils::filter_skip_named(fields).next().expect("Exactly one field");
					let field_name = &field.ident;
					let constructor = quote!( #name { #( #recurse, )* });
					(&field.ty, quote!(&self.#field_name), constructor)
				},
				Fields::Unnamed(ref fields) if utils::filter_skip_unnamed(fields).count() == 1 => {
					let recurse = fields.unnamed.iter().enumerate().map(|(_, f) | {
						let val_or_default = val_or_default(&f);
						quote_spanned!(f.span()=> #val_or_default)
					});
					let (id, field) = utils::filter_skip_unnamed(fields).next().expect("Exactly one field");
					let id = syn::Index::from(id);
					let constructor = quote!( #name(#( #recurse, )*));
					(&field.ty, quote!(&self.#id), constructor)
				},
				_ => {
					return Error::new(
						data.fields.span(),
						"Only structs with a single non-skipped field can derive CompactAs"
					).to_compile_error().into();
				},
			}
		},
		Data::Enum(syn::DataEnum { enum_token: syn::token::Enum { span }, .. }) |
		Data::Union(syn::DataUnion { union_token: syn::token::Union { span }, .. }) => {
			return Error::new(span, "Only structs can derive CompactAs").to_compile_error().into();
		},
	};

	let impl_block = quote! {
		impl #impl_generics _parity_scale_codec::CompactAs for #name #ty_generics #where_clause {
			type As = #inner_ty;
			fn encode_as(&self) -> &#inner_ty {
				#inner_field
			}
			fn decode_from(x: #inner_ty) -> #name #ty_generics {
				#constructor
			}
		}

		impl #impl_generics From<_parity_scale_codec::Compact<#name #ty_generics>> for #name #ty_generics #where_clause {
			fn from(x: _parity_scale_codec::Compact<#name #ty_generics>) -> #name #ty_generics {
				x.0
			}
		}
	};

	wrap_with_dummy_const(impl_block)
}