more comments, sync check

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm/src/block/builder.rs

@@ -2,15 +2,18 @@ use bytes::BufMut;
 
 use super::{Block, SIZEOF_U16};
 
-/// Builds a block
+/// Builds a block.
 pub struct BlockBuilder {
+    /// Offsets of each key-value entries.
     offsets: Vec<u16>,
+    /// All key-value pairs in the block.
     data: Vec<u8>,
+    /// The expected block size.
     block_size: usize,
 }
 
 impl BlockBuilder {
-    /// Creates a new block builder
+    /// Creates a new block builder.
     pub fn new(block_size: usize) -> Self {
         Self {
             offsets: Vec::new(),
@@ -23,7 +26,7 @@ impl BlockBuilder {
         self.offsets.len() * SIZEOF_U16 + self.data.len() + SIZEOF_U16
     }
 
-    /// Adds a key-value pair to the block
+    /// Adds a key-value pair to the block. Returns false when the block is full.
     #[must_use]
     pub fn add(&mut self, key: &[u8], value: &[u8]) -> bool {
         assert!(!key.is_empty(), "key must not be empty");
@@ -41,11 +44,12 @@ impl BlockBuilder {
         true
     }
 
+    /// Check if there is no key-value pair in the block.
     pub fn is_empty(&self) -> bool {
         self.offsets.is_empty()
     }
 
-    /// Builds a block
+    /// Finalize the block.
     pub fn build(self) -> Block {
         if self.is_empty() {
             panic!("block should not be empty");