add iter_on_single_itemsclippy lint (#8542)

Cargo.toml

@@ -155,6 +155,7 @@ useless_let_if_seq = "warn"
 use_self = "warn"
 missing_const_for_fn = "warn"
 empty_line_after_doc_comments = "warn"
+iter_on_single_items = "warn"
 
 # These are nursery lints which have findings. Allow them for now. Some are not
 # quite mature enough for use in our codebase and some we don't really want.
@@ -165,7 +166,6 @@ collection_is_never_read = "allow"
 debug_assert_with_mut_call = "allow"
 fallible_impl_from = "allow"
 future_not_send = "allow"
-iter_on_single_items = "allow"
 needless_collect = "allow"
 non_send_fields_in_send_ty = "allow"
 redundant_pub_crate = "allow"

crates/consensus/beacon/src/engine/mod.rs

@@ -2325,7 +2325,7 @@ mod tests {
                     chain_spec.clone(),
                     StaticFileProvider::read_write(static_dir_path).unwrap(),
                 ),
-                [&next_head].into_iter(),
+                std::iter::once(&next_head),
             );
 
             let expected_result = ForkchoiceUpdated::from_status(PayloadStatusEnum::Syncing);
@@ -2695,7 +2695,7 @@ mod tests {
                     chain_spec.clone(),
                     StaticFileProvider::read_write(static_dir_path).unwrap(),
                 ),
-                [&genesis].into_iter(),
+                std::iter::once(&genesis),
             );
 
             let mut engine_rx = spawn_consensus_engine(consensus_engine);

crates/trie/trie/src/hashed_cursor/post_state.rs

@@ -689,7 +689,7 @@ mod tests {
         let tx = db.tx().unwrap();
         let factory = HashedPostStateCursorFactory::new(&tx, &sorted);
         let expected =
-            [(address, db_storage.into_iter().chain(post_state_storage).collect())].into_iter();
+            std::iter::once((address, db_storage.into_iter().chain(post_state_storage).collect()));
         assert_storage_cursor_order(&factory, expected);
     }
 
@@ -724,11 +724,10 @@ mod tests {
         let sorted = hashed_post_state.into_sorted();
         let tx = db.tx().unwrap();
         let factory = HashedPostStateCursorFactory::new(&tx, &sorted);
-        let expected = [(
+        let expected = std::iter::once((
             address,
             post_state_storage.into_iter().filter(|(_, value)| *value > U256::ZERO).collect(),
-        )]
-        .into_iter();
+        ));
         assert_storage_cursor_order(&factory, expected);
     }
 
@@ -762,7 +761,7 @@ mod tests {
         let sorted = hashed_post_state.into_sorted();
         let tx = db.tx().unwrap();
         let factory = HashedPostStateCursorFactory::new(&tx, &sorted);
-        let expected = [(address, post_state_storage)].into_iter();
+        let expected = std::iter::once((address, post_state_storage));
         assert_storage_cursor_order(&factory, expected);
     }
 
@@ -797,7 +796,7 @@ mod tests {
         let sorted = hashed_post_state.into_sorted();
         let tx = db.tx().unwrap();
         let factory = HashedPostStateCursorFactory::new(&tx, &sorted);
-        let expected = [(address, storage)].into_iter();
+        let expected = std::iter::once((address, storage));
         assert_storage_cursor_order(&factory, expected);
     }