Fix Rust 1.37.0 compiler warnings (#5530)

Looks like most usages of trait objects should have introduced
a type variable instead.

kvstore/src/lib.rs

@@ -332,7 +332,7 @@ fn load_tables(root: &Path, mapper: &dyn Mapper) -> Result<Vec<BTreeMap<Key, SST
     Ok(tables)
 }
 
-fn dump_tables(root: &Path, mapper: &Mapper) -> Result<()> {
+fn dump_tables(root: &Path, mapper: &dyn Mapper) -> Result<()> {
     mapper.serialize_state_to(&root.join(TABLES_FILE))?;
     Ok(())
 }

kvstore/src/mapper.rs

@@ -12,7 +12,7 @@ pub use self::disk::Disk;
 pub use self::memory::Memory;
 
 pub trait Mapper: std::fmt::Debug + Send + Sync {
-    fn make_table(&self, kind: Kind, func: &mut FnMut(Writer, Writer)) -> Result<SSTable>;
+    fn make_table(&self, kind: Kind, func: &mut dyn FnMut(Writer, Writer)) -> Result<SSTable>;
     fn rotate_tables(&self) -> Result<()>;
     fn empty_trash(&self) -> Result<()>;
     fn active_set(&self) -> Result<Vec<SSTable>>;

kvstore/src/mapper/disk.rs

@@ -78,7 +78,7 @@ impl Disk {
 }
 
 impl Mapper for Disk {
-    fn make_table(&self, kind: Kind, func: &mut FnMut(Writer, Writer)) -> Result<SSTable> {
+    fn make_table(&self, kind: Kind, func: &mut dyn FnMut(Writer, Writer)) -> Result<SSTable> {
         let storage = self.choose_storage();
 
         let id = next_id(kind);

kvstore/src/mapper/memory.rs

@@ -51,7 +51,7 @@ impl Memory {
 }
 
 impl Mapper for Memory {
-    fn make_table(&self, kind: Kind, func: &mut FnMut(Writer, Writer)) -> Result<SSTable> {
+    fn make_table(&self, kind: Kind, func: &mut dyn FnMut(Writer, Writer)) -> Result<SSTable> {
         let backing = self.get_backing(kind);
         let id = next_id();
 

kvstore/src/writelog.rs

@@ -109,7 +109,7 @@ trait LogWriter: std::fmt::Debug + Write + Send + Sync {
 /// Holds actual logging related state
 #[derive(Debug)]
 struct Logger {
-    writer: Box<LogWriter>,
+    writer: Box<dyn LogWriter>,
 }
 
 impl Logger {