Fix call enum's metadata regression (#3513)

This fixes an issue introduced in
https://github.com/paritytech/substrate/pull/14101, in which I removed
the `Call` enum's documentation and replaced it with a link to the
`Pallet` struct, but this also removed any docs related to call from the
metadata.

I tried to add a regression test for this, but it seems to me that this
is not possible, given that using `type-info` we only assert in type-ids
for `Call`, `Event` and `Error`. I removed some doc comments from a test
setup in `frame-support-test` to demonstrate the issue there. @jsdw do
you have any comments on this?

I also fixed a small issue in the custom html/css of `polkadot-sdk-doc`
crate, making sure it does not affect the rust-doc page of all other
crates.

- [x] Investigate a regression test
- [x] prdoc

substrate/frame/support/test/tests/pallet.rs

@@ -209,7 +209,7 @@ pub mod pallet {
 	where
 		T::AccountId: From<SomeType1> + From<SomeType3> + SomeAssociation1,
 	{
-		/// Doc comment put in metadata
+		/// call foo doc comment put in metadata
 		#[pallet::call_index(0)]
 		#[pallet::weight(Weight::from_parts(*foo as u64, 0))]
 		pub fn foo(
@@ -225,7 +225,7 @@ pub mod pallet {
 			Ok(().into())
 		}
 
-		/// Doc comment put in metadata
+		/// call foo_storage_layer doc comment put in metadata
 		#[pallet::call_index(1)]
 		#[pallet::weight({1})]
 		pub fn foo_storage_layer(
@@ -270,7 +270,7 @@ pub mod pallet {
 	#[pallet::error]
 	#[derive(PartialEq, Eq)]
 	pub enum Error<T> {
-		/// doc comment put into metadata
+		/// error doc comment put in metadata
 		InsufficientProposersBalance,
 		NonExistentStorageValue,
 		Code(u8),
@@ -287,9 +287,8 @@ pub mod pallet {
 	where
 		T::AccountId: SomeAssociation1 + From<SomeType1>,
 	{
-		/// doc comment put in metadata
+		/// event doc comment put in metadata
 		Proposed(<T as frame_system::Config>::AccountId),
-		/// doc
 		Spending(BalanceOf<T>),
 		Something(u32),
 		SomethingElse(<T::AccountId as SomeAssociation1>::_1),
@@ -750,8 +749,7 @@ pub type UncheckedExtrinsic =
 	sp_runtime::testing::TestXt<RuntimeCall, frame_system::CheckNonZeroSender<Runtime>>;
 
 frame_support::construct_runtime!(
-	pub struct Runtime
-	{
+	pub struct Runtime {
 		// Exclude part `Storage` in order not to check its metadata in tests.
 		System: frame_system exclude_parts { Pallet, Storage },
 		Example: pallet,
@@ -772,6 +770,14 @@ fn _ensure_call_is_correctly_excluded_and_included(call: RuntimeCall) {
 	}
 }
 
+fn maybe_docs(doc: Vec<&'static str>) -> Vec<&'static str> {
+	if cfg!(feature = "no-metadata-docs") {
+		vec![]
+	} else {
+		doc
+	}
+}
+
 #[test]
 fn transactional_works() {
 	TestExternalities::default().execute_with(|| {
@@ -1362,19 +1368,47 @@ fn migrate_from_pallet_version_to_storage_version() {
 	});
 }
 
+#[test]
+fn pallet_item_docs_in_metadata() {
+	// call
+	let call_variants = match meta_type::<pallet::Call<Runtime>>().type_info().type_def {
+		scale_info::TypeDef::Variant(variants) => variants.variants,
+		_ => unreachable!(),
+	};
+
+	assert_eq!(call_variants[0].docs, maybe_docs(vec!["call foo doc comment put in metadata"]));
+	assert_eq!(
+		call_variants[1].docs,
+		maybe_docs(vec!["call foo_storage_layer doc comment put in metadata"])
+	);
+	assert!(call_variants[2].docs.is_empty());
+
+	// event
+	let event_variants = match meta_type::<pallet::Event<Runtime>>().type_info().type_def {
+		scale_info::TypeDef::Variant(variants) => variants.variants,
+		_ => unreachable!(),
+	};
+
+	assert_eq!(event_variants[0].docs, maybe_docs(vec!["event doc comment put in metadata"]));
+	assert!(event_variants[1].docs.is_empty());
+
+	// error
+	let error_variants = match meta_type::<pallet::Error<Runtime>>().type_info().type_def {
+		scale_info::TypeDef::Variant(variants) => variants.variants,
+		_ => unreachable!(),
+	};
+
+	assert_eq!(error_variants[0].docs, maybe_docs(vec!["error doc comment put in metadata"]));
+	assert!(error_variants[1].docs.is_empty());
+
+	// storage is already covered in the main `fn metadata` test.
+}
+
 #[test]
 fn metadata() {
 	use codec::Decode;
 	use frame_metadata::{v15::*, *};
 
-	fn maybe_docs(doc: Vec<&'static str>) -> Vec<&'static str> {
-		if cfg!(feature = "no-metadata-docs") {
-			vec![]
-		} else {
-			doc
-		}
-	}
-
 	let readme = "Support code for the runtime.\n\nLicense: Apache-2.0\n";
 	let expected_pallet_doc = vec![" Pallet documentation", readme, readme];