Support tree rebalancing

3 files changed, 32 insertions, 4 deletions

diff --git a/src/parser/event_parser/grammar/items.rs b/src/parser/event_parser/grammar/items.rs
index 522986ed0..725f04d1e 100644
--- a/src/parser/event_parser/grammar/items.rs
+++ b/src/parser/event_parser/grammar/items.rs
@@ -32,6 +32,7 @@ fn mod_contents_item(p: &mut Parser) {
 }
 
 fn item(p: &mut Parser) -> bool {
+    let attrs_start = p.mark();
     attributes::outer_attributes(p);
     visibility(p);
     //    node_if(p, USE_KW, USE_ITEM, use_item)
@@ -41,11 +42,17 @@ fn item(p: &mut Parser) -> bool {
     // || unsafe trait, impl
     // || node_if(p, FN_KW, FN_ITEM, fn_item)
     // || node_if(p, TYPE_KW, TYPE_ITEM, type_item)
-    node_if(p, [EXTERN_KW, CRATE_KW], EXTERN_CRATE_ITEM, extern_crate_item)
+    let item_start = p.mark();
+    let item_parsed = node_if(p, [EXTERN_KW, CRATE_KW], EXTERN_CRATE_ITEM, extern_crate_item)
         || node_if(p, MOD_KW, MOD_ITEM, mod_item)
         || node_if(p, USE_KW, USE_ITEM, use_item)
         || node_if(p, STRUCT_KW, STRUCT_ITEM, struct_item)
-        || node_if(p, FN_KW, FN_ITEM, fn_item)
+        || node_if(p, FN_KW, FN_ITEM, fn_item);
+
+    if item_parsed && attrs_start != item_start {
+        p.forward_parent(attrs_start, item_start);
+    }
+    item_parsed
 }
 
 fn struct_item(p: &mut Parser) {
diff --git a/src/parser/event_parser/mod.rs b/src/parser/event_parser/mod.rs
index 87b317c84..c89a3ebe7 100644
--- a/src/parser/event_parser/mod.rs
+++ b/src/parser/event_parser/mod.rs
@@ -5,7 +5,10 @@ mod parser;
 
 #[derive(Debug)]
 pub(crate) enum Event {
-    Start { kind: SyntaxKind },
+    Start {
+        kind: SyntaxKind,
+        forward_parent: Option<u32>,
+    },
     Finish,
     Token {
         kind: SyntaxKind,
diff --git a/src/parser/event_parser/parser.rs b/src/parser/event_parser/parser.rs
index 8bc382b12..14c0efe2d 100644
--- a/src/parser/event_parser/parser.rs
+++ b/src/parser/event_parser/parser.rs
@@ -22,6 +22,9 @@ pub(crate) struct Parser<'t> {
 #[derive(Debug, Clone, Copy,PartialEq, Eq)]
 pub(crate) struct Pos(u32);
 
+#[derive(Debug, Clone, Copy,PartialEq, Eq)]
+pub(crate) struct Mark(u32);
+
 impl<'t> Parser<'t> {
     pub(crate) fn new(text: &'t str, raw_tokens: &'t [Token]) -> Parser<'t> {
         let mut tokens = Vec::new();
@@ -47,6 +50,21 @@ impl<'t> Parser<'t> {
         }
     }
 
+    pub(crate) fn mark(&self) -> Mark {
+        Mark(self.events.len() as u32)
+    }
+
+    pub(crate) fn forward_parent(&mut self, child: Mark, parent: Mark) {
+        assert!(child.0 < parent.0);
+        let diff = parent.0 - child.0;
+        match self.events[child.0 as usize] {
+            Event::Start { ref mut forward_parent, .. } => {
+                *forward_parent = Some(diff);
+            }
+            _ => unreachable!()
+        }
+    }
+
     pub(crate) fn pos(&self) -> Pos {
         Pos(self.pos as u32)
     }
@@ -71,7 +89,7 @@ impl<'t> Parser<'t> {
     }
 
     pub(crate) fn start(&mut self, kind: SyntaxKind) {
-        self.event(Event::Start { kind });
+        self.event(Event::Start { kind, forward_parent: None });
     }
 
     pub(crate) fn finish(&mut self) {