Implements pallet versioning (#7208)

* Start

* Make macro work

* Rename `ModuleToIndex` to `PalletRuntimeSetup`

Besides the renaming it also adds support getting the name of a pallet
as configured in the runtime.

* Rename it to `PalletInfo`

* Remove accidentally added files

* Some work

* Make everything compile

* Adds a test and fixes some bugs

* Implement ordering for `PalletVersion`

* Apply suggestions from code review

* Review feedback

* Update frame/support/src/dispatch.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Update frame/support/src/dispatch.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fix compilation

* Fix test

* Fix doc test

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

substrate/frame/support/procedural/src/lib.rs

@@ -21,6 +21,7 @@
 
 mod storage;
 mod construct_runtime;
+mod pallet_version;
 mod transactional;
 mod debug_no_bound;
 mod clone_no_bound;
@@ -402,3 +403,8 @@ pub fn derive_eq_no_bound(input: TokenStream) -> TokenStream {
 pub fn require_transactional(attr: TokenStream, input: TokenStream) -> TokenStream {
 	transactional::require_transactional(attr, input).unwrap_or_else(|e| e.to_compile_error().into())
 }
+
+#[proc_macro]
+pub fn crate_to_pallet_version(input: TokenStream) -> TokenStream {
+	pallet_version::crate_to_pallet_version(input).unwrap_or_else(|e| e.to_compile_error()).into()
+}

substrate/frame/support/procedural/src/pallet_version.rs

@@ -0,0 +1,64 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2020 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.
+
+//! Implementation of macros related to pallet versioning.
+
+use proc_macro2::{TokenStream, Span};
+use syn::{Result, Error};
+use std::{env, str::FromStr};
+use frame_support_procedural_tools::generate_crate_access_2018;
+
+/// Get the version from the given version environment variable.
+///
+/// The version is parsed into the requested destination type.
+fn get_version<T: FromStr>(version_env: &str) -> std::result::Result<T, ()> {
+	let version = env::var(version_env)
+		.expect(&format!("`{}` is always set by cargo; qed", version_env));
+
+	T::from_str(&version).map_err(drop)
+}
+
+/// Create an error that will be shown by rustc at the call site of the macro.
+fn create_error(message: &str) -> Error {
+	Error::new(Span::call_site(), message)
+}
+
+/// Implementation of the `crate_to_pallet_version!` macro.
+pub fn crate_to_pallet_version(input: proc_macro::TokenStream) -> Result<TokenStream> {
+	if !input.is_empty() {
+		return Err(create_error("No arguments expected!"))
+	}
+
+	let major_version = get_version::<u16>("CARGO_PKG_VERSION_MAJOR")
+		.map_err(|_| create_error("Major version needs to fit into `u16`"))?;
+
+	let minor_version = get_version::<u8>("CARGO_PKG_VERSION_MINOR")
+		.map_err(|_| create_error("Minor version needs to fit into `u8`"))?;
+
+	let patch_version = get_version::<u8>("CARGO_PKG_VERSION_PATCH")
+		.map_err(|_| create_error("Patch version needs to fit into `u8`"))?;
+
+	let crate_ = generate_crate_access_2018()?;
+
+	Ok(quote::quote! {
+		#crate_::traits::PalletVersion {
+			major: #major_version,
+			minor: #minor_version,
+			patch: #patch_version,
+		}
+	})
+}