Adds ability to use default hasher in dev_mode for explicit key binding

frame/support/procedural/src/lib.rs

@@ -468,7 +468,8 @@ pub fn construct_runtime(input: TokenStream) -> TokenStream {
 ///   storage types. This is equivalent to specifying `#[pallet::unbounded]` on all storage type
 ///   definitions.
 /// * Storage hashers no longer need to be specified and can be replaced by `_`. In dev mode, these
-///   will be replaced by `Blake2_128Concat`.
+///   will be replaced by `Blake2_128Concat`. In case of explicit key-binding, `Hasher` can simply
+///   be ignored when in `dev_mode`.
 ///
 /// Note that the `dev_mode` argument can only be supplied to the `#[pallet]` or
 /// `#[frame_support::pallet]` attribute macro that encloses your pallet module. This argument

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

@@ -332,6 +332,7 @@ fn process_named_generics(
 	storage: &StorageKind,
 	args_span: proc_macro2::Span,
 	args: &[syn::AssocType],
+	dev_mode: bool,
 ) -> syn::Result<(Option<StorageGenerics>, Metadata, Option<syn::Type>, bool)> {
 	let mut parsed = HashMap::<String, syn::AssocType>::new();
 
@@ -346,6 +347,14 @@ fn process_named_generics(
 		parsed.insert(arg.ident.to_string(), arg.clone());
 	}
 
+	let mut map_mandatory_generics = vec!["Key", "Value"];
+	let mut map_optional_generics = vec!["QueryKind", "OnEmpty", "MaxValues"];
+	if dev_mode {
+		map_optional_generics.push("Hasher");
+	} else {
+		map_mandatory_generics.push("Hasher");
+	}
+
 	let generics = match storage {
 		StorageKind::Value => {
 			check_generics(
@@ -368,8 +377,8 @@ fn process_named_generics(
 		StorageKind::Map => {
 			check_generics(
 				&parsed,
-				&["Hasher", "Key", "Value"],
-				&["QueryKind", "OnEmpty", "MaxValues"],
+				&map_mandatory_generics,
+				&map_optional_generics,
 				"StorageMap",
 				args_span,
 			)?;
@@ -378,7 +387,7 @@ fn process_named_generics(
 				hasher: parsed
 					.remove("Hasher")
 					.map(|binding| binding.ty)
-					.expect("checked above as mandatory generic"),
+					.unwrap_or(syn::parse_quote!(Blake2_128Concat)),
 				key: parsed
 					.remove("Key")
 					.map(|binding| binding.ty)
@@ -395,8 +404,8 @@ fn process_named_generics(
 		StorageKind::CountedMap => {
 			check_generics(
 				&parsed,
-				&["Hasher", "Key", "Value"],
-				&["QueryKind", "OnEmpty", "MaxValues"],
+				&map_mandatory_generics,
+				&map_optional_generics,
 				"CountedStorageMap",
 				args_span,
 			)?;
@@ -405,7 +414,7 @@ fn process_named_generics(
 				hasher: parsed
 					.remove("Hasher")
 					.map(|binding| binding.ty)
-					.expect("checked above as mandatory generic"),
+					.unwrap_or(syn::Type::Verbatim(quote::quote! { Blake2_128Concat })),
 				key: parsed
 					.remove("Key")
 					.map(|binding| binding.ty)
@@ -420,10 +429,17 @@ fn process_named_generics(
 			}
 		},
 		StorageKind::DoubleMap => {
+			let mut double_map_mandatory_generics = vec!["Key1", "Key2", "Value"];
+			if dev_mode {
+				map_optional_generics.extend(["Hasher1", "Hasher2"]);
+			} else {
+				double_map_mandatory_generics.extend(["Hasher1", "Hasher2"]);
+			}
+
 			check_generics(
 				&parsed,
-				&["Hasher1", "Key1", "Hasher2", "Key2", "Value"],
-				&["QueryKind", "OnEmpty", "MaxValues"],
+				&double_map_mandatory_generics,
+				&map_optional_generics,
 				"StorageDoubleMap",
 				args_span,
 			)?;
@@ -432,15 +448,15 @@ fn process_named_generics(
 				hasher1: parsed
 					.remove("Hasher1")
 					.map(|binding| binding.ty)
-					.expect("checked above as mandatory generic"),
+					.unwrap_or(syn::parse_quote!(Blake2_128Concat)),
 				key1: parsed
 					.remove("Key1")
 					.map(|binding| binding.ty)
 					.expect("checked above as mandatory generic"),
 				hasher2: parsed
 					.remove("Hasher2")
 					.map(|binding| binding.ty)
-					.expect("checked above as mandatory generic"),
+					.unwrap_or(syn::parse_quote!(Blake2_128Concat)),
 				key2: parsed
 					.remove("Key2")
 					.map(|binding| binding.ty)
@@ -619,7 +635,7 @@ fn process_generics(
 				_ => unreachable!("It is asserted above that all generics are bindings"),
 			})
 			.collect::<Vec<_>>();
-		process_named_generics(&storage_kind, args_span, &args)
+		process_named_generics(&storage_kind, args_span, &args, dev_mode)
 	} else {
 		let msg = "Invalid pallet::storage, invalid generic declaration for storage. Expect only \
 			type generics or binding generics, e.g. `<Name1 = Gen1, Name2 = Gen2, ..>` or \

frame/support/test/tests/pallet_ui/non_dev_mode_storage_map_explicit_key_default_hasher.rs

@@ -0,0 +1,33 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+pub use pallet::*;
+
+#[frame_support::pallet]
+pub mod pallet {
+	use frame_support::pallet_prelude::*;
+
+	// The struct on which we build all of our Pallet logic.
+	#[pallet::pallet]
+	pub struct Pallet<T>(_);
+
+	// Your Pallet's configuration trait, representing custom external types and interfaces.
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::storage]
+	type MyStorage<T: Config> = StorageValue<_, Vec<u8>>;
+
+	#[pallet::storage]
+	type MyStorageMap<T: Config> = StorageMap<Key = u32, Value = u64>;
+
+	#[pallet::storage]
+	type MyStorageDoubleMap<T: Config> = StorageDoubleMap<Key1 = u32, Key2 = u64, Value = u64>;
+
+	#[pallet::storage]
+	type MyCountedStorageMap<T: Config> = CountedStorageMap<Key = u32, Value = u64>;
+
+	// Your Pallet's internal functions.
+	impl<T: Config> Pallet<T> {}
+}
+
+fn main() {}

frame/support/test/tests/pallet_ui/non_dev_mode_storage_map_explicit_key_default_hasher.stderr

@@ -0,0 +1,11 @@
+error: Invalid pallet::storage, cannot find `Hasher` generic, required for `StorageMap`.
+  --> tests/pallet_ui/dev_mode_explicit_key_without_arg_default_hasher.rs:21:43
+   |
+21 |     type MyStorageMap<T: Config> = StorageMap<Key = u32, Value = u64>;
+   |                                              ^
+
+error[E0432]: unresolved import `pallet`
+ --> tests/pallet_ui/dev_mode_explicit_key_without_arg_default_hasher.rs:3:9
+  |
+3 | pub use pallet::*;
+  |         ^^^^^^ help: a similar path exists: `test_pallet::pallet`

frame/support/test/tests/pallet_ui/pass/dev_mode_valid.rs

@@ -35,6 +35,15 @@ pub mod pallet {
 	#[pallet::storage]
 	type MyCountedStorageMap<T: Config> = CountedStorageMap<_, _, u32, u64>;
 
+	#[pallet::storage]
+	pub type MyStorageMap2<T: Config> = StorageMap<Key = u32, Value = u64>;
+
+	#[pallet::storage]
+	type MyStorageDoubleMap2<T: Config> = StorageDoubleMap<Key1 = u32, Key2 = u64, Value = u64>;
+
+	#[pallet::storage]
+	type MyCountedStorageMap2<T: Config> = CountedStorageMap<Key = u32, Value = u64>;
+
 	// Your Pallet's callable functions.
 	#[pallet::call]
 	impl<T: Config> Pallet<T> {