Apply suggestions from code review

Co-authored-by: str4d <[email protected]>

Author: nuttycom

zcash_client_sqlite/src/wallet/common.rs

@@ -31,7 +31,7 @@ fn per_protocol_names(protocol: ShieldedProtocol) -> (&'static str, &'static str
 fn unscanned_tip_exists(
     conn: &Connection,
     anchor_height: BlockHeight,
-    table_prefix: &str,
+    table_prefix: &'static str,
 ) -> Result<bool, rusqlite::Error> {
     // v_sapling_shard_unscanned_ranges only returns ranges ending on or after wallet birthday, so
     // we don't need to refer to the birthday in this query.
@@ -140,8 +140,6 @@ where
     // 3) Select all notes for which the running sum was less than the required value, as
     //    well as a single note for which the sum was greater than or equal to the
     //    required value, bringing the sum of all selected notes across the threshold.
-    //
-    // 4) Match the selected notes against the witnesses at the desired height.
     let mut stmt_select_notes = conn.prepare_cached(
         &format!(
             "WITH eligible AS (

zcash_client_sqlite/src/wallet/orchard.rs

@@ -140,6 +140,13 @@ fn to_spendable_note<P: consensus::Parameters>(
     let ufvk_str: Option<String> = row.get(8)?;
     let scope_code: Option<i64> = row.get(9)?;
 
+    // If we don't have information about the recipient key scope or the ufvk we can't determine
+    // which spending key to use. This may be because the received note was associated with an
+    // imported viewing key, so we treat such notes as not spendable. Although this method is
+    // presently only called using the results of queries where both the ufvk and
+    // recipient_key_scope columns are checked to be non-null, this is method is written
+    // defensively to account for the fact that both of these are nullable columns in case it
+    // is used elsewhere in the future.
     ufvk_str
         .zip(scope_code)
         .map(|(ufvk_str, scope_code)| {
@@ -176,10 +183,6 @@ fn to_spendable_note<P: consensus::Parameters>(
         .transpose()
 }
 
-// The `clippy::let_and_return` lint is explicitly allowed here because a bug in Clippy
-// (https://github.com/rust-lang/rust-clippy/issues/11308) means it fails to identify that the `result` temporary
-// is required in order to resolve the borrows involved in the `query_and_then` call.
-#[allow(clippy::let_and_return)]
 pub(crate) fn get_spendable_orchard_note<P: consensus::Parameters>(
     conn: &Connection,
     params: &P,