Use proc macros to generate conversion functions for MultiLocation (#3635)

* Use proc macros to generate conversion functions for MultiLocation

* Add compile test and missing conversion cases

* Add common derives for Parent and Ancestor

* Generate conversion functions for MultiLocation v0 via proc macro

* Add type conversion test and fix a bug

* cargo fmt

* Do not hardcode 8 as the number of max parents

* Use map instead of for loops when generating code fragments

* Spelling

* cargo fmt

* More mapping, less for-looping

Author: KiChjang

Cargo.lock

@@ -43,6 +43,7 @@ members = [
 	"xcm/xcm-simulator",
 	"xcm/xcm-simulator/example",
 	"xcm/pallet-xcm",
+	"xcm/procedural",
 	"node/client",
 	"node/collation-generation",
 	"node/core/approval-voting",

Cargo.toml

@@ -10,6 +10,7 @@ impl-trait-for-tuples = "0.2.0"
 parity-scale-codec = { version = "2.0.0", default-features = false, features = [ "derive" ] }
 derivative = {version = "2.2.0", default-features = false, features = [ "use_core" ] }
 log = { version = "0.4.14", default-features = false }
+xcm-procedural = { path = "procedural" }
 
 [features]
 default = ["std"]

xcm/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+authors = ["Parity Technologies <admin@parity.io>"]
+name = "xcm-procedural"
+version = "0.1.0"
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0.28"
+quote = "1.0.9"
+syn = "1.0.74"

xcm/procedural/Cargo.toml

@@ -0,0 +1,36 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Procedural macros used in XCM.
+
+use proc_macro::TokenStream;
+
+mod v0;
+mod v1;
+
+#[proc_macro]
+pub fn impl_conversion_functions_for_multilocation_v0(input: TokenStream) -> TokenStream {
+	v0::multilocation::generate_conversion_functions(input)
+		.unwrap_or_else(syn::Error::into_compile_error)
+		.into()
+}
+
+#[proc_macro]
+pub fn impl_conversion_functions_for_multilocation_v1(input: TokenStream) -> TokenStream {
+	v1::multilocation::generate_conversion_functions(input)
+		.unwrap_or_else(syn::Error::into_compile_error)
+		.into()
+}

xcm/procedural/src/lib.rs

@@ -0,0 +1,17 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+pub mod multilocation;

xcm/procedural/src/v0.rs

@@ -0,0 +1,115 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use proc_macro2::{Span, TokenStream};
+use quote::{format_ident, quote};
+
+pub fn generate_conversion_functions(input: proc_macro::TokenStream) -> syn::Result<TokenStream> {
+	if !input.is_empty() {
+		return Err(syn::Error::new(Span::call_site(), "No arguments expected"))
+	}
+
+	let from_tuples = generate_conversion_from_tuples();
+	let from_v1 = generate_conversion_from_v1();
+
+	Ok(quote! {
+		#from_tuples
+		#from_v1
+	})
+}
+
+fn generate_conversion_from_tuples() -> TokenStream {
+	let from_tuples = (0..8usize)
+		.map(|num_junctions| {
+			let junctions =
+				(0..=num_junctions).map(|_| format_ident!("Junction")).collect::<Vec<_>>();
+			let idents = (0..=num_junctions).map(|i| format_ident!("j{}", i)).collect::<Vec<_>>();
+			let variant = &format_ident!("X{}", num_junctions + 1);
+			let array_size = num_junctions + 1;
+
+			quote! {
+				impl From<( #(#junctions,)* )> for MultiLocation {
+					fn from( ( #(#idents,)* ): ( #(#junctions,)* ) ) -> Self {
+						MultiLocation::#variant( #(#idents),* )
+					}
+				}
+
+				impl From<[Junction; #array_size]> for MultiLocation {
+					fn from(j: [Junction; #array_size]) -> Self {
+						let [#(#idents),*] = j;
+						MultiLocation::#variant( #(#idents),* )
+					}
+				}
+			}
+		})
+		.collect::<TokenStream>();
+
+	quote! {
+		impl From<()> for MultiLocation {
+			fn from(_: ()) -> Self {
+				MultiLocation::Null
+			}
+		}
+
+		impl From<Junction> for MultiLocation {
+			fn from(x: Junction) -> Self {
+				MultiLocation::X1(x)
+			}
+		}
+
+		impl From<[Junction; 0]> for MultiLocation {
+			fn from(_: [Junction; 0]) -> Self {
+				MultiLocation::Null
+			}
+		}
+
+		#from_tuples
+	}
+}
+
+fn generate_conversion_from_v1() -> TokenStream {
+	let match_variants = (0..8u8)
+		.map(|cur_num| {
+			let variant = format_ident!("X{}", cur_num + 1);
+			let idents = (1..=cur_num).map(|i| format_ident!("j{}", i)).collect::<Vec<_>>();
+
+			quote! {
+				crate::v1::Junctions::#variant( j0 #(, #idents)* ) => res
+					.pushed_with(Junction::from(j0))
+					#( .and_then(|res| res.pushed_with(Junction::from(#idents))) )*
+					.map_err(|_| ()),
+			}
+		})
+		.collect::<TokenStream>();
+
+	quote! {
+		impl TryFrom<crate::v1::MultiLocation> for MultiLocation {
+			type Error = ();
+			fn try_from(v1: crate::v1::MultiLocation) -> core::result::Result<Self, ()> {
+				let mut res = MultiLocation::Null;
+
+				for _ in 0..v1.parents {
+					res.push(Junction::Parent)?;
+				}
+
+				match v1.interior {
+					crate::v1::Junctions::Here => Ok(res),
+					#match_variants
+				}
+			}
+		}
+	}
+}

xcm/procedural/src/v0/multilocation.rs

@@ -0,0 +1,17 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+pub mod multilocation;