5 files changed, 46 insertions, 4 deletions

diff --git a/crates/libsyntax2/src/grammar/expressions/mod.rs b/crates/libsyntax2/src/grammar/expressions/mod.rs
index 59a0564d9..bd6c84886 100644
--- a/crates/libsyntax2/src/grammar/expressions/mod.rs
+++ b/crates/libsyntax2/src/grammar/expressions/mod.rs
@@ -25,7 +25,7 @@ fn expr_no_struct(p: &mut Parser) {
 // fn b() { let _ = 1; }
 // fn c() { 1; 2; }
 // fn d() { 1; 2 }
-pub(super) fn block(p: &mut Parser) {
+pub(crate) fn block(p: &mut Parser) {
     assert!(p.at(L_CURLY));
     let m = p.start();
     p.bump();
diff --git a/crates/libsyntax2/src/grammar/items/mod.rs b/crates/libsyntax2/src/grammar/items/mod.rs
index 206c85280..44ab92c63 100644
--- a/crates/libsyntax2/src/grammar/items/mod.rs
+++ b/crates/libsyntax2/src/grammar/items/mod.rs
@@ -1,10 +1,12 @@
-use super::*;
 
 mod consts;
 mod structs;
 mod traits;
 mod use_item;
 
+use super::*;
+pub(crate) use self::structs::named_field_def_list;
+
 // test mod_contents
 // fn foo() {}
 // macro_rules! foo {}
diff --git a/crates/libsyntax2/src/grammar/items/structs.rs b/crates/libsyntax2/src/grammar/items/structs.rs
index ca027d718..93d3381f8 100644
--- a/crates/libsyntax2/src/grammar/items/structs.rs
+++ b/crates/libsyntax2/src/grammar/items/structs.rs
@@ -82,7 +82,7 @@ fn enum_variant_list(p: &mut Parser) {
     m.complete(p, ENUM_VARIANT_LIST);
 }
 
-fn named_field_def_list(p: &mut Parser) {
+pub(crate) fn named_field_def_list(p: &mut Parser) {
     assert!(p.at(L_CURLY));
     let m = p.start();
     p.bump();
diff --git a/crates/libsyntax2/src/grammar/mod.rs b/crates/libsyntax2/src/grammar/mod.rs
index e3ca2714c..46ba8a89a 100644
--- a/crates/libsyntax2/src/grammar/mod.rs
+++ b/crates/libsyntax2/src/grammar/mod.rs
@@ -35,6 +35,10 @@ use {
     parser_api::{Marker, CompletedMarker, Parser, TokenSet},
     SyntaxKind::{self, *},
 };
+pub(crate) use self::{
+    expressions::block,
+    items::named_field_def_list,
+};
 
 pub(crate) fn file(p: &mut Parser) {
     let file = p.start();
diff --git a/crates/libsyntax2/src/lib.rs b/crates/libsyntax2/src/lib.rs
index 86fdbd23f..3a36a57b1 100644
--- a/crates/libsyntax2/src/lib.rs
+++ b/crates/libsyntax2/src/lib.rs
@@ -50,7 +50,11 @@ pub use {
     yellow::{SyntaxNode, SyntaxNodeRef, OwnedRoot, RefRoot, TreeRoot, SyntaxError},
 };
 
-use yellow::{GreenNode, SyntaxRoot};
+use {
+    SyntaxKind::*,
+    yellow::{GreenNode, SyntaxRoot},
+    parser_api::Parser,
+};
 
 #[derive(Clone, Debug)]
 pub struct File {
@@ -69,6 +73,22 @@ impl File {
         let (root, errors) = parser_impl::parse::<yellow::GreenBuilder>(text, &tokens);
         File::new(root, errors)
     }
+    pub fn reparse(&self, edit: &AtomEdit) -> File {
+        self.incremental_reparse(edit).unwrap_or_else(|| {
+            self.full_reparse(edit)
+        })
+    }
+    fn incremental_reparse(&self, edit: &AtomEdit) -> Option<File> {
+        let (node, reparser) = find_reparsable_node(self.syntax(), edit.delete)?;
+        None
+    }
+    fn full_reparse(&self, edit: &AtomEdit) -> File {
+        let start = u32::from(edit.delete.start()) as usize;
+        let end = u32::from(edit.delete.end()) as usize;
+        let mut text = self.syntax().text();
+        text.replace_range(start..end, &edit.insert);
+        File::parse(&text)
+    }
     pub fn ast(&self) -> ast::Root {
         ast::Root::cast(self.syntax()).unwrap()
     }
@@ -132,3 +152,19 @@ impl AtomEdit {
         AtomEdit::replace(TextRange::offset_len(offset, 0.into()), text)
     }
 }
+
+fn find_reparsable_node(node: SyntaxNodeRef, range: TextRange) -> Option<(SyntaxNodeRef, fn(&mut Parser))> {
+    let node = algo::find_covering_node(node, range);
+    return algo::ancestors(node)
+        .filter_map(|node| reparser(node).map(|r| (node, r)))
+        .next();
+
+    fn reparser(node: SyntaxNodeRef) -> Option<fn(&mut Parser)> {
+        let res = match node.kind() {
+            BLOCK => grammar::block,
+            NAMED_FIELD_DEF_LIST => grammar::named_field_def_list,
+            _ => return None,
+        };
+        Some(res)
+    }
+}