From 6997adfee7a317ed758fa26e86298c7f1e4c01f0 Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Sat, 25 Sep 2021 18:07:51 +0300
Subject: [PATCH] simplify attribute parsing

---
 crates/parser/src/grammar/expressions.rs | 14 +++-------
 crates/parser/src/parser.rs              | 33 +++++++++---------------
 2 files changed, 16 insertions(+), 31 deletions(-)

diff --git a/crates/parser/src/grammar/expressions.rs b/crates/parser/src/grammar/expressions.rs
index ba64f58e6dc..30d3d4421ac 100644
--- a/crates/parser/src/grammar/expressions.rs
+++ b/crates/parser/src/grammar/expressions.rs
@@ -27,11 +27,7 @@ pub(super) fn expr_with_attrs(p: &mut Parser) -> bool {
     let success = cm.is_some();
 
     match (has_attrs, cm) {
-        (true, Some(cm)) => {
-            let kind = cm.kind();
-            cm.undo_completion(p).abandon(p);
-            m.complete(p, kind);
-        }
+        (true, Some(cm)) => cm.extend_to(p, m),
         _ => m.abandon(p),
     }
 
@@ -92,11 +88,9 @@ pub(super) fn stmt(p: &mut Parser, with_semi: StmtWithSemi, prefer_expr: bool) {
         //     { #[A] bar!()? }
         //     #[B] &()
         // }
-        if let Some(cm) = cm {
-            cm.undo_completion(p).abandon(p);
-            m.complete(p, kind);
-        } else {
-            m.abandon(p);
+        match cm {
+            Some(cm) => cm.extend_to(p, m),
+            None => m.abandon(p),
         }
     } else {
         // test no_semi_after_block
diff --git a/crates/parser/src/parser.rs b/crates/parser/src/parser.rs
index a3aca3d591d..f6b8308c57a 100644
--- a/crates/parser/src/parser.rs
+++ b/crates/parser/src/parser.rs
@@ -285,9 +285,8 @@ impl Marker {
             }
             _ => unreachable!(),
         }
-        let finish_pos = p.events.len() as u32;
         p.push_event(Event::Finish);
-        CompletedMarker::new(self.pos, finish_pos, kind)
+        CompletedMarker::new(self.pos, kind)
     }
 
     /// Abandons the syntax tree node. All its children
@@ -305,14 +304,13 @@ impl Marker {
 }
 
 pub(crate) struct CompletedMarker {
-    start_pos: u32,
-    finish_pos: u32,
+    pos: u32,
     kind: SyntaxKind,
 }
 
 impl CompletedMarker {
-    fn new(start_pos: u32, finish_pos: u32, kind: SyntaxKind) -> Self {
-        CompletedMarker { start_pos, finish_pos, kind }
+    fn new(pos: u32, kind: SyntaxKind) -> Self {
+        CompletedMarker { pos, kind }
     }
 
     /// This method allows to create a new node which starts
@@ -330,29 +328,22 @@ impl CompletedMarker {
     /// distance to `NEWSTART` into forward_parent(=2 in this case);
     pub(crate) fn precede(self, p: &mut Parser) -> Marker {
         let new_pos = p.start();
-        let idx = self.start_pos as usize;
+        let idx = self.pos as usize;
         match &mut p.events[idx] {
             Event::Start { forward_parent, .. } => {
-                *forward_parent = Some(new_pos.pos - self.start_pos);
+                *forward_parent = Some(new_pos.pos - self.pos);
             }
             _ => unreachable!(),
         }
         new_pos
     }
 
-    /// Undo this completion and turns into a `Marker`
-    pub(crate) fn undo_completion(self, p: &mut Parser) -> Marker {
-        let start_idx = self.start_pos as usize;
-        let finish_idx = self.finish_pos as usize;
-        match &mut p.events[start_idx] {
-            Event::Start { kind, forward_parent: None } => *kind = TOMBSTONE,
-            _ => unreachable!(),
-        }
-        match &mut p.events[finish_idx] {
-            slot @ Event::Finish => *slot = Event::tombstone(),
-            _ => unreachable!(),
-        }
-        Marker::new(self.start_pos)
+    /// Extends this completed marker *to the left* up to `m`.
+    pub(crate) fn extend_to(self, p: &mut Parser, mut m: Marker) {
+        assert!(m.pos <= self.pos);
+        m.bomb.defuse();
+
+        p.events.swap(self.pos as usize, m.pos as usize);
     }
 
     pub(crate) fn kind(&self) -> SyntaxKind {