fix(clippy): Resolve some lifetime and reference lints (#4578)

* Fix significant drop in match scrutinee

https://github.com/rust-lang/rust/issues/93883

* Fix deref immutable value

* Fix explicit 0 index when first() would do

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

zebra-chain/src/orchard/tree.rs

@@ -335,7 +335,8 @@ impl NoteCommitmentTree {
             .cached_root
             .write()
             .expect("a thread that previously held exclusive lock access panicked");
-        match *write_root {
+        let read_root = write_root.as_ref().cloned();
+        match read_root {
             // Another thread got write access first, return cached root.
             Some(root) => root,
             None => {

zebra-chain/src/sapling/tree.rs

@@ -340,7 +340,8 @@ impl NoteCommitmentTree {
             .cached_root
             .write()
             .expect("a thread that previously held exclusive lock access panicked");
-        match *write_root {
+        let read_root = write_root.as_ref().cloned();
+        match read_root {
             // Another thread got write access first, return cached root.
             Some(root) => root,
             None => {

zebra-chain/src/sprout/tree.rs

@@ -274,7 +274,8 @@ impl NoteCommitmentTree {
             .cached_root
             .write()
             .expect("a thread that previously held exclusive lock access panicked");
-        match *write_root {
+        let read_root = write_root.as_ref().cloned();
+        match read_root {
             // Another thread got write access first, return cached root.
             Some(root) => root,
             None => {

zebra-chain/src/transparent/serialize.rs

@@ -98,7 +98,7 @@ pub(crate) fn parse_coinbase_height(
     mut data: Vec<u8>,
 ) -> Result<(block::Height, CoinbaseData), SerializationError> {
     use block::Height;
-    match (data.get(0), data.len()) {
+    match (data.first(), data.len()) {
         // Blocks 1 through 16 inclusive encode block height with OP_N opcodes.
         (Some(op_n @ 0x51..=0x60), len) if len >= 1 => Ok((
             Height((op_n - 0x50) as u32),

zebra-state/src/service/chain_tip.rs

@@ -195,12 +195,18 @@ impl ChainTipSender {
         // a read-lock being created and living beyond the `self.sender.send(..)` call. If that
         // happens, the `send` method will attempt to obtain a write-lock and will dead-lock.
         // Without the binding, the guard is dropped at the end of the expression.
-        let needs_update = match (new_tip.as_ref(), self.sender.borrow().as_ref()) {
+        let active_hash = self
+            .sender
+            .borrow()
+            .as_ref()
+            .map(|active_value| active_value.hash);
+
+        let needs_update = match (new_tip.as_ref(), active_hash) {
             // since the blocks have been contextually validated,
             // we know their hashes cover all the block data
-            (Some(new_tip), Some(active_value)) => new_tip.hash != active_value.hash,
+            (Some(new_tip), Some(active_hash)) => new_tip.hash != active_hash,
             (Some(_new_tip), None) => true,
-            (None, _active_value) => false,
+            (None, _active_value_hash) => false,
         };
 
         if needs_update {

zebra-state/src/service/finalized_state/disk_format.rs

@@ -73,7 +73,7 @@ where
     type Bytes = T::Bytes;
 
     fn as_bytes(&self) -> Self::Bytes {
-        T::as_bytes(&*self)
+        T::as_bytes(self)
     }
 }