Adds UI test for error when _ is used without dev_mode

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

@@ -23,7 +23,7 @@ use crate::{
 	},
 };
 use quote::ToTokens;
-use std::{collections::HashMap, ops::{IndexMut, Index}};
+use std::{collections::HashMap, ops::{IndexMut}};
 use syn::spanned::Spanned;
 
 /// Generate the prefix_ident related to the storage.

frame/support/test/tests/pallet_ui/dev_mode_without_arg_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<_, _, u32, u64>;
+
+	#[pallet::storage]
+	type MyStorageDoubleMap<T: Config> = StorageDoubleMap<_, _, u32, _, u64, u64>;
+
+	#[pallet::storage]
+	type MyCountedStorageMap<T: Config> = CountedStorageMap<_, _, u32, u64>;
+
+	// Your Pallet's internal functions.
+	impl<T: Config> Pallet<T> {}
+}
+
+fn main() {}

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

@@ -0,0 +1,19 @@
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for type aliases
+  --> tests/pallet_ui/dev_mode_without_arg_default_hasher.rs:21:47
+   |
+21 |     type MyStorageMap<T: Config> = StorageMap<_, _, u32, u64>;
+   |                                                  ^ not allowed in type signatures
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for type aliases
+  --> tests/pallet_ui/dev_mode_without_arg_default_hasher.rs:24:59
+   |
+24 |     type MyStorageDoubleMap<T: Config> = StorageDoubleMap<_, _, u32, _, u64, u64>;
+   |                                                              ^       ^ not allowed in type signatures
+   |                                                              |
+   |                                                              not allowed in type signatures
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for type aliases
+  --> tests/pallet_ui/dev_mode_without_arg_default_hasher.rs:27:61
+   |
+27 |     type MyCountedStorageMap<T: Config> = CountedStorageMap<_, _, u32, u64>;
+   |                                                                ^ not allowed in type signatures

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

@@ -24,10 +24,10 @@ pub mod pallet {
 	type MyStorageMap<T: Config> = StorageMap<_, _, u32, u64>;
 
 	#[pallet::storage]
-	type MyStorageDoubleMap<T: Config> = StorageDoubleMap<_, _, u32, _, u64>;
+	type MyStorageDoubleMap<T: Config> = StorageDoubleMap<_, _, u32, _, u64, u64>;
 
 	#[pallet::storage]
-	type MyCountedStorageMap<T: Config> = CountedStorageMap<_, _, u32, _, u64>;
+	type MyCountedStorageMap<T: Config> = CountedStorageMap<_, _, u32, u64>;
 
 	// Your Pallet's callable functions.
 	#[pallet::call]