update genesis_config related docs and tests and error messages (pa…

…ritytech#1642)

Follow-up to paritytech/substrate#14306.

I hope this also showcases the important message of: **It is really not
that hard to make the examples codes in rust-docs compile, and therefore
remain correct. Please embrace this :)**

It moves the documentation of proc macros to their re-export, such that
can link other items in frame-support. This is a patter that we should
embrace for all of macro docs, and apply in PRs like
paritytech/substrate#13987 as well.

---------

Co-authored-by: Gonçalo Pestana <[email protected]>
Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: command-bot <>

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

@@ -1417,57 +1417,11 @@ pub fn type_value(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()
 }
 
-/// The `#[pallet::genesis_config]` attribute allows you to define the genesis configuration
-/// for the pallet.
-///
-/// Item is defined as either an enum or a struct. It needs to be public and implement the
-/// trait `GenesisBuild` with [`#[pallet::genesis_build]`](`macro@genesis_build`). The type
-/// generics are constrained to be either none, or `T` or `T: Config`.
-///
-/// E.g:
-///
-/// ```ignore
-/// #[pallet::genesis_config]
-/// pub struct GenesisConfig<T: Config> {
-/// 	_myfield: BalanceOf<T>,
-/// }
-/// ```
 #[proc_macro_attribute]
 pub fn genesis_config(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()
 }
 
-/// The `#[pallet::genesis_build]` attribute allows you to define how `genesis_configuration`
-/// is built. This takes as input the `GenesisConfig` type (as `self`) and constructs the pallet's
-/// initial state.
-///
-/// The impl must be defined as:
-///
-/// ```ignore
-/// #[pallet::genesis_build]
-/// impl<T: Config> GenesisBuild<T> for GenesisConfig<$maybe_generics> {
-/// 	fn build(&self) { $expr }
-/// }
-/// ```
-///
-/// I.e. a trait implementation with generic `T: Config`, of trait `GenesisBuild<T>` on
-/// type `GenesisConfig` with generics none or `T`.
-///
-/// E.g.:
-///
-/// ```ignore
-/// #[pallet::genesis_build]
-/// impl<T: Config> GenesisBuild<T> for GenesisConfig {
-/// 	fn build(&self) {}
-/// }
-/// ```
-///
-/// ## Macro expansion
-///
-/// The macro will add the following attribute:
-/// * `#[cfg(feature = "std")]`
-///
-/// The macro will implement `sp_runtime::BuildStorage`.
 #[proc_macro_attribute]
 pub fn genesis_build(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()

substrate/frame/support/procedural/src/pallet/expand/genesis_build.rs

@@ -38,7 +38,7 @@ pub fn expand_genesis_build(def: &mut Def) -> proc_macro2::TokenStream {
 		#[cfg(feature = "std")]
 			impl<#type_impl_gen> #frame_support::sp_runtime::BuildStorage for #gen_cfg_ident<#gen_cfg_use_gen> #where_clause
 			{
-				fn assimilate_storage(&self, storage: &mut sp_runtime::Storage) -> std::result::Result<(), std::string::String> {
+				fn assimilate_storage(&self, storage: &mut #frame_support::sp_runtime::Storage) -> std::result::Result<(), std::string::String> {
 					#frame_support::__private::BasicExternalities::execute_with_storage(storage, || {
 						self.build();
 						Ok(())

substrate/frame/support/procedural/src/pallet/parse/helper.rs

@@ -494,7 +494,7 @@ pub fn check_type_def_gen(
 /// return the instance if found for `GenesisBuild`
 /// return None for BuildGenesisConfig
 pub fn check_genesis_builder_usage(type_: &syn::Path) -> syn::Result<Option<InstanceUsage>> {
-	let expected = "expected `GenesisBuild<T>` or `GenesisBuild<T, I>`";
+	let expected = "expected `BuildGenesisConfig` (or the deprecated `GenesisBuild<T>` or `GenesisBuild<T, I>`)";
 	pub struct Checker(Option<InstanceUsage>);
 	impl syn::parse::Parse for Checker {
 		fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {

substrate/frame/support/src/lib.rs

@@ -2188,10 +2188,80 @@ pub mod pallet_macros {
 	pub use frame_support_procedural::{
 		call_index, compact, composite_enum, config, constant,
 		disable_frame_system_supertrait_check, error, event, extra_constants, generate_deposit,
-		generate_store, genesis_build, genesis_config, getter, hooks, import_section, inherent,
-		no_default, no_default_bounds, origin, pallet_section, storage, storage_prefix,
-		storage_version, type_value, unbounded, validate_unsigned, weight, whitelist_storage,
+		generate_store, getter, hooks, import_section, inherent, no_default, no_default_bounds,
+		origin, pallet_section, storage, storage_prefix, storage_version, type_value, unbounded,
+		validate_unsigned, weight, whitelist_storage,
 	};
+
+	/// Allows you to define the genesis configuration for the pallet.
+	///
+	/// Item is defined as either an enum or a struct. It needs to be public and implement the
+	/// trait [`frame_support::traits::BuildGenesisConfig`].
+	///
+	/// See [`genesis_build`] for an example.
+	pub use frame_support_procedural::genesis_config;
+
+	/// Allows you to define how the state of your pallet at genesis is built. This
+	/// takes as input the `GenesisConfig` type (as `self`) and constructs the pallet's initial
+	/// state.
+	///
+	/// The fields of the `GenesisConfig` can in turn be populated by the chain-spec.
+	///
+	/// ## Example:
+	///
+	/// ```
+	/// #[frame_support::pallet]
+	/// pub mod pallet {
+	/// # 	#[pallet::config]
+	/// # 	pub trait Config: frame_system::Config {}
+	/// # 	#[pallet::pallet]
+	/// # 	pub struct Pallet<T>(_);
+	/// # 	use frame_support::traits::BuildGenesisConfig;
+	///     #[pallet::genesis_config]
+	///     #[derive(frame_support::DefaultNoBound)]
+	///     pub struct GenesisConfig<T: Config> {
+	///         foo: Vec<T::AccountId>
+	///     }
+	///
+	///     #[pallet::genesis_build]
+	///     impl<T: Config> BuildGenesisConfig for GenesisConfig<T> {
+	///         fn build(&self) {
+	///             // use &self to access fields.
+	///             let foo = &self.foo;
+	///             todo!()
+	///         }
+	///     }
+	/// }
+	/// ```
+	///
+	/// ## Former Usage
+	///
+	/// Prior to <https://github.com/paritytech/substrate/pull/14306>, the following syntax was used.
+	/// This is deprecated and will soon be removed.
+	///
+	/// ```
+	/// #[frame_support::pallet]
+	/// pub mod pallet {
+	/// #     #[pallet::config]
+	/// #     pub trait Config: frame_system::Config {}
+	/// #     #[pallet::pallet]
+	/// #     pub struct Pallet<T>(_);
+	/// #     use frame_support::traits::GenesisBuild;
+	///     #[pallet::genesis_config]
+	///     #[derive(frame_support::DefaultNoBound)]
+	///     pub struct GenesisConfig<T: Config> {
+	/// 		foo: Vec<T::AccountId>
+	/// 	}
+	///
+	///     #[pallet::genesis_build]
+	///     impl<T: Config> GenesisBuild<T> for GenesisConfig<T> {
+	///         fn build(&self) {
+	///             todo!()
+	///         }
+	///     }
+	/// }
+	/// ```
+	pub use frame_support_procedural::genesis_build;
 }
 
 #[deprecated(note = "Will be removed after July 2023; Use `sp_runtime::traits` directly instead.")]

substrate/frame/support/test/tests/pallet_ui/genesis_invalid_generic.stderr

@@ -1,4 +1,4 @@
-error: Invalid genesis builder: expected `GenesisBuild<T>` or `GenesisBuild<T, I>`
+error: Invalid genesis builder: expected `BuildGenesisConfig` (or the deprecated `GenesisBuild<T>` or `GenesisBuild<T, I>`)
   --> tests/pallet_ui/genesis_invalid_generic.rs:36:7
    |
 36 |     impl GenesisBuild for GenesisConfig {}