Support extra constant renaming

frame/support/procedural/src/pallet/expand/constants.rs

@@ -26,6 +26,8 @@ struct ConstDef {
 	pub doc: Vec<syn::Lit>,
 	/// default_byte implementation
 	pub default_byte_impl: proc_macro2::TokenStream,
+	/// Constant name for Metadata (optional)
+	pub metadata_name: Option<syn::Ident>,
 }
 
 ///
@@ -54,6 +56,7 @@ pub fn expand_constants(def: &mut Def) -> proc_macro2::TokenStream {
 					#frame_support::traits::Get<#const_type>>::get();
 				#frame_support::codec::Encode::encode(&value)
 			),
+			metadata_name: None,
 		}
 	});
 
@@ -68,13 +71,14 @@ pub fn expand_constants(def: &mut Def) -> proc_macro2::TokenStream {
 				let value = <Pallet<#type_use_gen>>::#ident();
 				#frame_support::codec::Encode::encode(&value)
 			),
+			metadata_name: const_.metadata_name.clone(),
 		}
 	});
 
 	let consts = config_consts.chain(extra_consts).map(|const_| {
 		let const_type = &const_.type_;
-		let ident = &const_.ident;
-		let ident_str = format!("{}", ident);
+		let ident_str = format!("{}", const_.metadata_name.unwrap_or(const_.ident));
+
 		let doc = const_.doc.clone().into_iter();
 		let default_byte_impl = &const_.default_byte_impl;
 

frame/support/procedural/src/pallet/parse/extra_constants.rs

@@ -28,6 +28,7 @@ mod keyword {
 	syn::custom_keyword!(compact);
 	syn::custom_keyword!(T);
 	syn::custom_keyword!(pallet);
+	syn::custom_keyword!(constant_name);
 }
 
 /// Definition of extra constants typically `impl<T: Config> Pallet<T> { ... }`
@@ -50,14 +51,40 @@ pub struct ExtraConstantDef {
 	pub type_: syn::Type,
 	/// The doc associated
 	pub doc: Vec<syn::Lit>,
+	/// Optional MetaData Name
+	pub metadata_name: Option<syn::Ident>,
+}
+
+/// Attributes for functions in extra_constants impl block.
+/// Parse for `#[pallet::constant_name(ConstantName)]`
+pub struct ExtraConstAttr {
+	metadata_name: syn::Ident,
+}
+
+impl syn::parse::Parse for ExtraConstAttr {
+	fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+		input.parse::<syn::Token![#]>()?;
+		let content;
+		syn::bracketed!(content in input);
+		content.parse::<keyword::pallet>()?;
+		content.parse::<syn::Token![::]>()?;
+		content.parse::<keyword::constant_name>()?;
+
+		let metadata_name;
+		syn::parenthesized!(metadata_name in content);
+		Ok(ExtraConstAttr { metadata_name: metadata_name.parse::<syn::Ident>()? })
+	}
 }
 
 impl ExtraConstantsDef {
 	pub fn try_from(index: usize, item: &mut syn::Item) -> syn::Result<Self> {
 		let item = if let syn::Item::Impl(item) = item {
 			item
 		} else {
-			return Err(syn::Error::new(item.span(), "Invalid pallet::call, expected item impl"))
+			return Err(syn::Error::new(
+				item.span(),
+				"Invalid pallet::extra_constants, expected item impl",
+			))
 		};
 
 		let mut instances = vec![];
@@ -102,10 +129,23 @@ impl ExtraConstantsDef {
 				syn::ReturnType::Type(_, type_) => *type_.clone(),
 			};
 
+			// parse metadata_name
+			let mut extra_constant_attrs: Vec<ExtraConstAttr> =
+				helper::take_item_pallet_attrs(method)?;
+
+			if extra_constant_attrs.len() > 1 {
+				let msg =
+					"Invalid attribute in pallet::constant_name, only one attribute is expected";
+				return Err(syn::Error::new(extra_constant_attrs[1].metadata_name.span(), msg))
+			}
+
+			let metadata_name = extra_constant_attrs.pop().map(|attr| attr.metadata_name);
+
 			extra_constants.push(ExtraConstantDef {
 				ident: method.sig.ident.clone(),
 				type_,
 				doc: get_doc_literals(&method.attrs),
+				metadata_name,
 			});
 		}
 

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

@@ -139,6 +139,12 @@ impl MutItemAttrs for syn::ItemMod {
 	}
 }
 
+impl MutItemAttrs for syn::ImplItemMethod {
+	fn mut_item_attrs(&mut self) -> Option<&mut Vec<syn::Attribute>> {
+		Some(&mut self.attrs)
+	}
+}
+
 /// Parse for `()`
 struct Unit;
 impl syn::parse::Parse for Unit {

frame/support/test/tests/pallet.rs

@@ -146,6 +146,12 @@ pub mod pallet {
 		fn some_extra_extra() -> T::AccountId {
 			SomeType1.into()
 		}
+
+		/// Some doc
+		#[pallet::constant_name(SomeExtraRename)]
+		fn some_extra_rename() -> T::AccountId {
+			SomeType1.into()
+		}
 	}
 
 	#[pallet::pallet]
@@ -1220,6 +1226,12 @@ fn metadata() {
 					value: vec![0, 0, 0, 0, 0, 0, 0, 0],
 					docs: vec![" Some doc"],
 				},
+				PalletConstantMetadata {
+					name: "SomeExtraRename",
+					ty: meta_type::<u64>(),
+					value: vec![0, 0, 0, 0, 0, 0, 0, 0],
+					docs: vec![" Some doc"],
+				},
 			],
 			error: Some(PalletErrorMetadata { ty: meta_type::<pallet::Error<Runtime>>() }),
 		},