Fix clippy warnings (#691)

src/compaction_filter.rs

@@ -100,7 +100,7 @@ pub unsafe extern "C" fn destructor_callback<F>(raw_cb: *mut c_void)
 where
     F: CompactionFilter,
 {
-    Box::from_raw(raw_cb as *mut F);
+    drop(Box::from_raw(raw_cb as *mut F));
 }
 
 pub unsafe extern "C" fn name_callback<F>(raw_cb: *mut c_void) -> *const c_char

src/compaction_filter_factory.rs

@@ -30,7 +30,7 @@ pub unsafe extern "C" fn destructor_callback<F>(raw_self: *mut c_void)
 where
     F: CompactionFilterFactory,
 {
-    Box::from_raw(raw_self as *mut F);
+    drop(Box::from_raw(raw_self as *mut F));
 }
 
 pub unsafe extern "C" fn name_callback<F>(raw_self: *mut c_void) -> *const c_char

src/comparator.rs

@@ -26,7 +26,7 @@ pub struct ComparatorCallback {
 }
 
 pub unsafe extern "C" fn destructor_callback(raw_cb: *mut c_void) {
-    Box::from_raw(raw_cb as *mut ComparatorCallback);
+    drop(Box::from_raw(raw_cb as *mut ComparatorCallback));
 }
 
 pub unsafe extern "C" fn name_callback(raw_cb: *mut c_void) -> *const c_char {

src/merge_operator.rs

@@ -77,7 +77,7 @@ pub struct MergeOperatorCallback<F: MergeFn, PF: MergeFn> {
 }
 
 pub unsafe extern "C" fn destructor_callback<F: MergeFn, PF: MergeFn>(raw_cb: *mut c_void) {
-    Box::from_raw(raw_cb as *mut MergeOperatorCallback<F, PF>);
+    drop(Box::from_raw(raw_cb as *mut MergeOperatorCallback<F, PF>));
 }
 
 pub unsafe extern "C" fn delete_callback(
@@ -86,10 +86,10 @@ pub unsafe extern "C" fn delete_callback(
     value_length: size_t,
 ) {
     if !value.is_null() {
-        Box::from_raw(slice::from_raw_parts_mut(
+        drop(Box::from_raw(slice::from_raw_parts_mut(
             value as *mut u8,
             value_length as usize,
-        ));
+        )));
     }
 }
 

src/slice_transform.rs

@@ -83,7 +83,7 @@ pub struct TransformCallback<'a> {
 }
 
 pub unsafe extern "C" fn slice_transform_destructor_callback(raw_cb: *mut c_void) {
-    Box::from_raw(raw_cb as *mut TransformCallback);
+    drop(Box::from_raw(raw_cb as *mut TransformCallback));
 }
 
 pub unsafe extern "C" fn slice_transform_name_callback(raw_cb: *mut c_void) -> *const c_char {

src/write_batch.rs

@@ -122,7 +122,7 @@ impl<const TRANSACTION: bool> WriteBatchWithTransaction<TRANSACTION> {
             );
             // we must manually set the raw box free since there is no
             // associated "destroy" callback for this object
-            Box::from_raw(state);
+            drop(Box::from_raw(state));
         }
     }