engine_traits: Stub out get_range_approximate_middle

Signed-off-by: Brian Anderson <andersrb@gmail.com>

components/engine_panic/src/range_properties.rs

@@ -27,4 +27,13 @@ impl RangePropertiesExt for PanicEngine {
     fn get_range_approximate_split_keys_cf(&self, cfname: &str, range: Range, region_id: u64, split_size: u64, max_size: u64, batch_split_limit: u64) -> Result<Vec<Vec<u8>>> {
         panic!()
     }
+
+    fn get_range_approximate_middle(&self, range: Range, region_id: u64) -> Result<Option<Vec<u8>>> {
+        panic!()
+    }
+
+    fn get_range_approximate_middle_cf(&self, cfname: &str, range: Range, region_id: u64) -> Result<Option<Vec<u8>>> {
+        panic!()
+    }
+
 }

components/engine_rocks/src/range_properties.rs

@@ -224,4 +224,13 @@ impl RangePropertiesExt for RocksEngine {
         }
         Ok(split_keys)
     }
+
+    fn get_range_approximate_middle(&self, range: Range, region_id: u64) -> Result<Option<Vec<u8>>> {
+        panic!()
+    }
+
+    fn get_range_approximate_middle_cf(&self, cfname: &str, range: Range, region_id: u64) -> Result<Option<Vec<u8>>> {
+        panic!()
+    }
+
 }

components/engine_traits/src/range_properties.rs

@@ -29,5 +29,18 @@ pub trait RangePropertiesExt {
     fn get_range_approximate_split_keys(&self, range: Range, region_id: u64, split_size: u64, max_size: u64, batch_split_limit: u64) -> Result<Vec<Vec<u8>>>;
 
     fn get_range_approximate_split_keys_cf(&self, cfname: &str, range: Range, region_id: u64, split_size: u64, max_size: u64, batch_split_limit: u64) -> Result<Vec<Vec<u8>>>;
+
+    /// Get range approximate middle key based on default and write cf size.
+    ///
+    /// The region_id is used only for logging and means nothing internally.
+    fn get_range_approximate_middle(&self, range: Range, region_id: u64) -> Result<Option<Vec<u8>>>;
+
+    /// Get the approximate middle key of the region. If we suppose the region
+    /// is stored on disk as a plain file, "middle key" means the key whose
+    /// position is in the middle of the file.
+    ///
+    /// The returned key maybe is timestamped if transaction KV is used,
+    /// and must start with "z".
+    fn get_range_approximate_middle_cf(&self, cfname: &str, range: Range, region_id: u64) -> Result<Option<Vec<u8>>>;
 }
 

components/raftstore/src/coprocessor/split_check/half.rs

@@ -133,6 +133,7 @@ pub fn get_region_approximate_middle(
 /// The returned key maybe is timestamped if transaction KV is used,
 /// and must start with "z".
 fn get_region_approximate_middle_cf(
+
     db: &impl KvEngine,
     cfname: &str,
     region: &Region,