Implement a CountedStorageMap (#9125)

* initial impl

* expose in pallet_prelude

* temp test

* Apply suggestions from code review

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Xiliang Chen <xlchen1291@gmail.com>

* implement with macro help.

* test for macro generation

* add iterable functions, some test and fixes

* fix merge

* doc

* Update frame/support/src/storage/types/counted_map.rs

Co-authored-by: Zeke Mostov <32168567+emostov@users.noreply.github.com>

* fix merge

* fmt

* fix spelling

* improve on removal

* fix partial storage info

* fmt

* add license

* suggested renames

* fix typo

* fix test

* fmt

* fix ui tests

* clearer doc

* better doc

* add metadata test

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Xiliang Chen <xlchen1291@gmail.com>
Co-authored-by: Zeke Mostov <32168567+emostov@users.noreply.github.com>

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

@@ -86,6 +86,7 @@ impl syn::parse::Parse for PalletStorageAttr {
 pub enum Metadata {
 	Value { value: syn::Type },
 	Map { value: syn::Type, key: syn::Type },
+	CountedMap { value: syn::Type, key: syn::Type },
 	DoubleMap { value: syn::Type, key1: syn::Type, key2: syn::Type },
 	NMap { keys: Vec<syn::Type>, keygen: syn::Type, value: syn::Type },
 }
@@ -153,6 +154,14 @@ pub enum StorageGenerics {
 		on_empty: Option<syn::Type>,
 		max_values: Option<syn::Type>,
 	},
+	CountedMap {
+		hasher: syn::Type,
+		key: syn::Type,
+		value: syn::Type,
+		query_kind: Option<syn::Type>,
+		on_empty: Option<syn::Type>,
+		max_values: Option<syn::Type>,
+	},
 	Value {
 		value: syn::Type,
 		query_kind: Option<syn::Type>,
@@ -173,6 +182,7 @@ impl StorageGenerics {
 		let res = match self.clone() {
 			Self::DoubleMap { value, key1, key2, .. } => Metadata::DoubleMap { value, key1, key2 },
 			Self::Map { value, key, .. } => Metadata::Map { value, key },
+			Self::CountedMap { value, key, .. } => Metadata::CountedMap { value, key },
 			Self::Value { value, .. } => Metadata::Value { value },
 			Self::NMap { keygen, value, .. } =>
 				Metadata::NMap { keys: collect_keys(&keygen)?, keygen, value },
@@ -186,6 +196,7 @@ impl StorageGenerics {
 		match &self {
 			Self::DoubleMap { query_kind, .. } |
 			Self::Map { query_kind, .. } |
+			Self::CountedMap { query_kind, .. } |
 			Self::Value { query_kind, .. } |
 			Self::NMap { query_kind, .. } => query_kind.clone(),
 		}
@@ -195,6 +206,7 @@ impl StorageGenerics {
 enum StorageKind {
 	Value,
 	Map,
+	CountedMap,
 	DoubleMap,
 	NMap,
 }
@@ -324,6 +336,33 @@ fn process_named_generics(
 				max_values: parsed.remove("MaxValues").map(|binding| binding.ty),
 			}
 		},
+		StorageKind::CountedMap => {
+			check_generics(
+				&parsed,
+				&["Hasher", "Key", "Value"],
+				&["QueryKind", "OnEmpty", "MaxValues"],
+				"CountedStorageMap",
+				args_span,
+			)?;
+
+			StorageGenerics::CountedMap {
+				hasher: parsed
+					.remove("Hasher")
+					.map(|binding| binding.ty)
+					.expect("checked above as mandatory generic"),
+				key: parsed
+					.remove("Key")
+					.map(|binding| binding.ty)
+					.expect("checked above as mandatory generic"),
+				value: parsed
+					.remove("Value")
+					.map(|binding| binding.ty)
+					.expect("checked above as mandatory generic"),
+				query_kind: parsed.remove("QueryKind").map(|binding| binding.ty),
+				on_empty: parsed.remove("OnEmpty").map(|binding| binding.ty),
+				max_values: parsed.remove("MaxValues").map(|binding| binding.ty),
+			}
+		},
 		StorageKind::DoubleMap => {
 			check_generics(
 				&parsed,
@@ -425,6 +464,11 @@ fn process_unnamed_generics(
 			Metadata::Map { key: retrieve_arg(2)?, value: retrieve_arg(3)? },
 			retrieve_arg(4).ok(),
 		),
+		StorageKind::CountedMap => (
+			None,
+			Metadata::CountedMap { key: retrieve_arg(2)?, value: retrieve_arg(3)? },
+			retrieve_arg(4).ok(),
+		),
 		StorageKind::DoubleMap => (
 			None,
 			Metadata::DoubleMap {
@@ -451,6 +495,7 @@ fn process_generics(
 	let storage_kind = match &*segment.ident.to_string() {
 		"StorageValue" => StorageKind::Value,
 		"StorageMap" => StorageKind::Map,
+		"CountedStorageMap" => StorageKind::CountedMap,
 		"StorageDoubleMap" => StorageKind::DoubleMap,
 		"StorageNMap" => StorageKind::NMap,
 		found => {