Implement StorageNMap (#8635)

* Implement StorageNMap

* Change copyright date to 2021

* Rewrite keys to use impl_for_tuples instead of recursion

* Implement prefix iteration on StorageNMap

* Implement EncodeLike for key arguments

* Rename KeyGenerator::Arg to KeyGenerator::KArg

* Support StorageNMap in decl_storage and #[pallet::storage] macros

* Use StorageNMap in assets pallet

* Support migrate_keys in StorageNMap

* Reduce line characters on select files

* Refactor crate imports in decl_storage macros

* Some more line char reductions and doc comment update

* Update UI test expectations

* Revert whitespace changes to untouched files

* Generate Key struct instead of a 1-tuple when only 1 pair of key and hasher is provided

* Revert formatting changes to unrelated files

* Introduce KeyGeneratorInner

* Add tests for StorageNMap in FRAMEv2 pallet macro

* Small fixes to unit tests for StorageNMap

* Bump runtime metadata version

* Remove unused import

* Update tests to use runtime metadata v13

* Introduce and use EncodeLikeTuple as a trait bound for KArg

* Add some rustdocs

* Revert usage of StorageNMap in assets pallet

* Make use of ext::PunctuatedTrailing

* Add rustdoc for final_hash

* Fix StorageNMap proc macro expansions for single key cases

* Create associated const in KeyGenerator for hasher metadata

* Refactor code according to comments from Basti

* Add module docs for generator/nmap.rs

* Re-export storage::Key as NMapKey in pallet prelude

* Seal the EncodeLikeTuple trait

* Extract sealing code out of key.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

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

@@ -29,6 +29,7 @@ mod keyword {
 	syn::custom_keyword!(get);
 	syn::custom_keyword!(map);
 	syn::custom_keyword!(double_map);
+	syn::custom_keyword!(nmap);
 	syn::custom_keyword!(opaque_blake2_256);
 	syn::custom_keyword!(opaque_blake2_128);
 	syn::custom_keyword!(blake2_128_concat);
@@ -199,6 +200,7 @@ impl_parse_for_opt!(DeclStorageBuild => keyword::build);
 enum DeclStorageType {
 	Map(DeclStorageMap),
 	DoubleMap(Box<DeclStorageDoubleMap>),
+	NMap(DeclStorageNMap),
 	Simple(syn::Type),
 }
 
@@ -208,6 +210,8 @@ impl syn::parse::Parse for DeclStorageType {
 			Ok(Self::Map(input.parse()?))
 		} else if input.peek(keyword::double_map) {
 			Ok(Self::DoubleMap(input.parse()?))
+		} else if input.peek(keyword::nmap) {
+			Ok(Self::NMap(input.parse()?))
 		} else {
 			Ok(Self::Simple(input.parse()?))
 		}
@@ -235,7 +239,21 @@ struct DeclStorageDoubleMap {
 	pub value: syn::Type,
 }
 
-#[derive(ToTokens, Debug)]
+#[derive(Parse, ToTokens, Debug)]
+struct DeclStorageKey {
+	pub hasher: Opt<SetHasher>,
+	pub key: syn::Type,
+}
+
+#[derive(Parse, ToTokens, Debug)]
+struct DeclStorageNMap {
+	pub map_keyword: keyword::nmap,
+	pub storage_keys: ext::PunctuatedTrailing<DeclStorageKey, Token![,]>,
+	pub ass_keyword: Token![=>],
+	pub value: syn::Type,
+}
+
+#[derive(Clone, ToTokens, Debug)]
 enum Hasher {
 	Blake2_256(keyword::opaque_blake2_256),
 	Blake2_128(keyword::opaque_blake2_128),
@@ -291,7 +309,7 @@ impl syn::parse::Parse for Opt<DeclStorageDefault> {
 	}
 }
 
-#[derive(Parse, ToTokens, Debug)]
+#[derive(Clone, Parse, ToTokens, Debug)]
 struct SetHasher {
 	pub hasher_keyword: keyword::hasher,
 	pub inner: ext::Parens<Hasher>,
@@ -495,6 +513,18 @@ fn parse_storage_line_defs(
 					value: map.value,
 				})
 			),
+			DeclStorageType::NMap(map) => super::StorageLineTypeDef::NMap(
+				super::NMapDef {
+					hashers: map
+						.storage_keys
+						.inner
+						.iter()
+						.map(|pair| Ok(pair.hasher.inner.clone().ok_or_else(no_hasher_error)?.into()))
+						.collect::<Result<Vec<_>, syn::Error>>()?,
+					keys: map.storage_keys.inner.iter().map(|pair| pair.key.clone()).collect(),
+					value: map.value,
+				}
+			),
 			DeclStorageType::Simple(expr) => super::StorageLineTypeDef::Simple(expr),
 		};