refactor(flow): refine comments and code (#3785)

* refactor(flow): refine comments and code

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

* doc: description of the properties of removed keys

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>

* fix: `get`'s fast path for cur val

---------

Signed-off-by: Zhenchi <zhongzc_arch@outlook.com>
Co-authored-by: discord9 <discord9@163.com>

src/flow/src/compute/render/map.rs

@@ -124,7 +124,6 @@ fn mfp_subgraph(
     // 1. Read all updates that were emitted between the last time this arrangement had updates and the current time.
     // 2. Output the updates.
     // 3. Truncate all updates within that range.
-
     let from = arrange.read().last_compaction_time().map(|n| n + 1);
     let from = from.unwrap_or(repr::Timestamp::MIN);
     let output_kv = arrange.read().get_updates_in_range(from..=now);
@@ -135,7 +134,7 @@ fn mfp_subgraph(
         .collect_vec();
     send.give(output);
     let run_compaction = || {
-        arrange.write().compaction_to(now)?;
+        arrange.write().compact_to(now)?;
         Ok(())
     };
     err_collector.run(run_compaction);

src/flow/src/compute/state.rs

@@ -46,9 +46,7 @@ pub struct DataflowState {
 
 impl DataflowState {
     pub fn new_arrange(&mut self, name: Option<Vec<String>>) -> ArrangeHandler {
-        let arrange = name
-            .map(Arrangement::new_with_name)
-            .unwrap_or_else(Arrangement::new);
+        let arrange = name.map(Arrangement::new_with_name).unwrap_or_default();
 
         let arr = ArrangeHandler::from(arrange);
         // mark this arrange as used in this dataflow

src/flow/src/lib.rs

@@ -16,6 +16,7 @@
 //! It can transform substrait plan into it's own plan and execute it.
 //! It also contains definition of expression, adapter and plan, and internal state management.
 
+#![feature(let_chains)]
 #![allow(dead_code)]
 #![allow(unused_imports)]
 #![warn(missing_docs)]