Adds support for generics inderive-impl (#5584)

As raised by @kianenigma in
sam0x17/macro_magic#15, this PR adds the
support for generics while using `derive_impl`.

This can then be used in conjunction with `FliteFrameSystem` being
defined [here](https://github.com/kianenigma/flite) as
```diff
+#[derive_impl(FliteFrameSystem<Configuration>)]
impl frame_system::Config for Runtime {
  type Block = Block;

  // .. Rest can be removed
}
```

---------

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

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

@@ -17,13 +17,13 @@
 
 //! Implementation of the `derive_impl` attribute macro.
 
-use derive_syn_parse::Parse;
 use macro_magic::mm_core::ForeignPath;
 use proc_macro2::TokenStream as TokenStream2;
 use quote::{quote, ToTokens};
 use std::collections::HashSet;
 use syn::{
-	parse2, parse_quote, spanned::Spanned, token, Ident, ImplItem, ItemImpl, Path, Result, Token,
+	parse2, parse_quote, spanned::Spanned, token, AngleBracketedGenericArguments, Ident, ImplItem,
+	ItemImpl, Path, PathArguments, PathSegment, Result, Token,
 };
 
 mod keyword {
@@ -56,18 +56,60 @@ fn is_runtime_type(item: &syn::ImplItemType) -> bool {
 		false
 	})
 }
-
-#[derive(Parse, Debug)]
 pub struct DeriveImplAttrArgs {
 	pub default_impl_path: Path,
+	pub generics: Option<AngleBracketedGenericArguments>,
 	_as: Option<Token![as]>,
-	#[parse_if(_as.is_some())]
 	pub disambiguation_path: Option<Path>,
 	_comma: Option<Token![,]>,
-	#[parse_if(_comma.is_some())]
 	pub no_aggregated_types: Option<keyword::no_aggregated_types>,
 }
 
+impl syn::parse::Parse for DeriveImplAttrArgs {
+	fn parse(input: syn::parse::ParseStream) -> Result<Self> {
+		let mut default_impl_path: Path = input.parse()?;
+		// Extract the generics if any
+		let (default_impl_path, generics) = match default_impl_path.clone().segments.last() {
+			Some(PathSegment { ident, arguments: PathArguments::AngleBracketed(args) }) => {
+				default_impl_path.segments.pop();
+				default_impl_path
+					.segments
+					.push(PathSegment { ident: ident.clone(), arguments: PathArguments::None });
+				(default_impl_path, Some(args.clone()))
+			},
+			Some(PathSegment { arguments: PathArguments::None, .. }) => (default_impl_path, None),
+			_ => return Err(syn::Error::new(default_impl_path.span(), "Invalid default impl path")),
+		};
+
+		let lookahead = input.lookahead1();
+		let (_as, disambiguation_path) = if lookahead.peek(Token![as]) {
+			let _as: Token![as] = input.parse()?;
+			let disambiguation_path: Path = input.parse()?;
+			(Some(_as), Some(disambiguation_path))
+		} else {
+			(None, None)
+		};
+
+		let lookahead = input.lookahead1();
+		let (_comma, no_aggregated_types) = if lookahead.peek(Token![,]) {
+			let _comma: Token![,] = input.parse()?;
+			let no_aggregated_types: keyword::no_aggregated_types = input.parse()?;
+			(Some(_comma), Some(no_aggregated_types))
+		} else {
+			(None, None)
+		};
+
+		Ok(DeriveImplAttrArgs {
+			default_impl_path,
+			generics,
+			_as,
+			disambiguation_path,
+			_comma,
+			no_aggregated_types,
+		})
+	}
+}
+
 impl ForeignPath for DeriveImplAttrArgs {
 	fn foreign_path(&self) -> &Path {
 		&self.default_impl_path
@@ -77,6 +119,7 @@ impl ForeignPath for DeriveImplAttrArgs {
 impl ToTokens for DeriveImplAttrArgs {
 	fn to_tokens(&self, tokens: &mut TokenStream2) {
 		tokens.extend(self.default_impl_path.to_token_stream());
+		tokens.extend(self.generics.to_token_stream());
 		tokens.extend(self._as.to_token_stream());
 		tokens.extend(self.disambiguation_path.to_token_stream());
 		tokens.extend(self._comma.to_token_stream());
@@ -117,6 +160,7 @@ fn combine_impls(
 	default_impl_path: Path,
 	disambiguation_path: Path,
 	inject_runtime_types: bool,
+	generics: Option<AngleBracketedGenericArguments>,
 ) -> ItemImpl {
 	let (existing_local_keys, existing_unsupported_items): (HashSet<ImplItem>, HashSet<ImplItem>) =
 		local_impl
@@ -155,7 +199,7 @@ fn combine_impls(
 				// modify and insert uncolliding type items
 				let modified_item: ImplItem = parse_quote! {
 					#( #cfg_attrs )*
-					type #ident = <#default_impl_path as #disambiguation_path>::#ident;
+					type #ident = <#default_impl_path #generics as #disambiguation_path>::#ident;
 				};
 				return Some(modified_item)
 			}
@@ -216,6 +260,7 @@ pub fn derive_impl(
 	local_tokens: TokenStream2,
 	disambiguation_path: Option<Path>,
 	no_aggregated_types: Option<keyword::no_aggregated_types>,
+	generics: Option<AngleBracketedGenericArguments>,
 ) -> Result<TokenStream2> {
 	let local_impl = parse2::<ItemImpl>(local_tokens)?;
 	let foreign_impl = parse2::<ItemImpl>(foreign_tokens)?;
@@ -234,6 +279,7 @@ pub fn derive_impl(
 		default_impl_path,
 		disambiguation_path,
 		no_aggregated_types.is_none(),
+		generics,
 	);
 
 	Ok(quote!(#combined_impl))
@@ -301,3 +347,16 @@ fn test_disambiguation_path() {
 		compute_disambiguation_path(None, foreign_impl.clone(), parse_quote!(SomeType));
 	assert_eq!(disambiguation_path.unwrap(), parse_quote!(SomeTrait));
 }
+
+#[test]
+fn test_derive_impl_attr_args_parsing_with_generic() {
+	let args = parse2::<DeriveImplAttrArgs>(quote!(
+		some::path::TestDefaultConfig<Config> as some::path::DefaultConfig
+	))
+	.unwrap();
+	assert_eq!(args.default_impl_path, parse_quote!(some::path::TestDefaultConfig));
+	assert_eq!(args.generics.unwrap().args[0], parse_quote!(Config));
+	let args = parse2::<DeriveImplAttrArgs>(quote!(TestDefaultConfig<Config2>)).unwrap();
+	assert_eq!(args.default_impl_path, parse_quote!(TestDefaultConfig));
+	assert_eq!(args.generics.unwrap().args[0], parse_quote!(Config2));
+}

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

@@ -683,6 +683,7 @@ pub fn derive_impl(attrs: TokenStream, input: TokenStream) -> TokenStream {
 		input.into(),
 		custom_attrs.disambiguation_path,
 		custom_attrs.no_aggregated_types,
+		custom_attrs.generics,
 	)
 	.unwrap_or_else(|r| r.into_compile_error())
 	.into()