Support extra constant renaming (#9814)

* Rebased with master. Resolved merge conflict in
frame/support/test/tests/pallet.rs

* Switching Account ID to SomeType1, as SomeType3 was giving me conversion error.

* Wrong indent config.  Fixed.

* These tabs look fine locally, but look different on Github.  Trying to get the style config right.

* Parsing pallet::constant_name.
Passing unit tests, which is confusing because I didn't change `ident` in the ExtraConstantDef initialization.

* Finalized parsing of extra constant name by adding optional metadata field.
Added expansion logic that replaces respective `idents` where they exist.

* Erasing this to try to keep the format the same across the source code.

* Another formatting change for consistency.

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

strictly more idiomatic.

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

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

strictly idiomatic change.

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

* Fixing formatting and CI warnings.

* switched to nightly compiler to use rustfmt.toml

Co-authored-by: Eric Miller <emiller@lirio.co>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

substrate/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> { ... }`
@@ -50,6 +51,29 @@ 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 {
@@ -57,7 +81,10 @@ impl ExtraConstantsDef {
 		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,
 			});
 		}
 

substrate/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 {