3 files changed, 73 insertions, 33 deletions

diff --git a/crates/ra_syntax/src/parsing/builder.rs b/crates/ra_syntax/src/parsing/builder.rs
index 0775b0900..cfe3139b8 100644
--- a/crates/ra_syntax/src/parsing/builder.rs
+++ b/crates/ra_syntax/src/parsing/builder.rs
@@ -1,4 +1,7 @@
+use std::mem;
+
 use ra_parser::{TreeSink, ParseError};
+use rowan::GreenNodeBuilder;
 
 use crate::{
     SmolStr, SyntaxError, SyntaxErrorKind, TextUnit, TextRange,
@@ -7,19 +10,32 @@ use crate::{
     syntax_node::{GreenNode, RaTypes},
 };
 
-use rowan::GreenNodeBuilder;
-
+/// Bridges the parser with our specific syntax tree representation.
+///
+/// `TreeBuilder` also handles attachment of trivia (whitespace) to nodes.
 pub(crate) struct TreeBuilder<'a> {
     text: &'a str,
     tokens: &'a [Token],
     text_pos: TextUnit,
     token_pos: usize,
+    state: State,
     errors: Vec<SyntaxError>,
     inner: GreenNodeBuilder<RaTypes>,
 }
 
+enum State {
+    PendingStart,
+    Normal,
+    PendingFinish,
+}
+
 impl<'a> TreeSink for TreeBuilder<'a> {
     fn leaf(&mut self, kind: SyntaxKind, n_tokens: u8) {
+        match mem::replace(&mut self.state, State::Normal) {
+            State::PendingStart => unreachable!(),
+            State::PendingFinish => self.inner.finish_internal(),
+            State::Normal => (),
+        }
         self.eat_trivias();
         let n_tokens = n_tokens as usize;
         let len = self.tokens[self.token_pos..self.token_pos + n_tokens]
@@ -29,11 +45,18 @@ impl<'a> TreeSink for TreeBuilder<'a> {
         self.do_leaf(kind, len, n_tokens);
     }
 
-    fn start_branch(&mut self, kind: SyntaxKind, root: bool) {
-        if root {
-            self.inner.start_internal(kind);
-            return;
+    fn start_branch(&mut self, kind: SyntaxKind) {
+        match mem::replace(&mut self.state, State::Normal) {
+            State::PendingStart => {
+                self.inner.start_internal(kind);
+                // No need to attach trivias to previous node: there is no
+                // previous node.
+                return;
+            }
+            State::PendingFinish => self.inner.finish_internal(),
+            State::Normal => (),
         }
+
         let n_trivias =
             self.tokens[self.token_pos..].iter().take_while(|it| it.kind.is_trivia()).count();
         let leading_trivias = &self.tokens[self.token_pos..self.token_pos + n_trivias];
@@ -54,11 +77,12 @@ impl<'a> TreeSink for TreeBuilder<'a> {
         self.eat_n_trivias(n_attached_trivias);
     }
 
-    fn finish_branch(&mut self, root: bool) {
-        if root {
-            self.eat_trivias()
+    fn finish_branch(&mut self) {
+        match mem::replace(&mut self.state, State::PendingFinish) {
+            State::PendingStart => unreachable!(),
+            State::PendingFinish => self.inner.finish_internal(),
+            State::Normal => (),
         }
-        self.inner.finish_internal();
     }
 
     fn error(&mut self, error: ParseError) {
@@ -74,12 +98,21 @@ impl<'a> TreeBuilder<'a> {
             tokens,
             text_pos: 0.into(),
             token_pos: 0,
+            state: State::PendingStart,
             errors: Vec::new(),
             inner: GreenNodeBuilder::new(),
         }
     }
 
-    pub(super) fn finish(self) -> (GreenNode, Vec<SyntaxError>) {
+    pub(super) fn finish(mut self) -> (GreenNode, Vec<SyntaxError>) {
+        match mem::replace(&mut self.state, State::Normal) {
+            State::PendingFinish => {
+                self.eat_trivias();
+                self.inner.finish_internal()
+            }
+            State::PendingStart | State::Normal => unreachable!(),
+        }
+
         (self.inner.finish(), self.errors)
     }
 
diff --git a/crates/ra_syntax/src/parsing/input.rs b/crates/ra_syntax/src/parsing/input.rs
index 58be795bc..31c6a3b9b 100644
--- a/crates/ra_syntax/src/parsing/input.rs
+++ b/crates/ra_syntax/src/parsing/input.rs
@@ -5,6 +5,26 @@ use crate::{
     parsing::lexer::Token,
 };
 
+pub(crate) struct ParserInput<'t> {
+    text: &'t str,
+    /// start position of each token(expect whitespace and comment)
+    /// ```non-rust
+    ///  struct Foo;
+    /// ^------^---
+    /// |      |  ^-
+    /// 0      7  10
+    /// ```
+    /// (token, start_offset): `[(struct, 0), (Foo, 7), (;, 10)]`
+    start_offsets: Vec<TextUnit>,
+    /// non-whitespace/comment tokens
+    /// ```non-rust
+    /// struct Foo {}
+    /// ^^^^^^ ^^^ ^^
+    /// ```
+    /// tokens: `[struct, Foo, {, }]`
+    tokens: Vec<Token>,
+}
+
 impl<'t> TokenSource for ParserInput<'t> {
     fn token_kind(&self, pos: usize) -> SyntaxKind {
         if !(pos < self.tokens.len()) {
@@ -28,26 +48,6 @@ impl<'t> TokenSource for ParserInput<'t> {
     }
 }
 
-pub(crate) struct ParserInput<'t> {
-    text: &'t str,
-    /// start position of each token(expect whitespace and comment)
-    /// ```non-rust
-    ///  struct Foo;
-    /// ^------^---
-    /// |      |  ^-
-    /// 0      7  10
-    /// ```
-    /// (token, start_offset): `[(struct, 0), (Foo, 7), (;, 10)]`
-    start_offsets: Vec<TextUnit>,
-    /// non-whitespace/comment tokens
-    /// ```non-rust
-    /// struct Foo {}
-    /// ^^^^^^ ^^^ ^^
-    /// ```
-    /// tokens: `[struct, Foo, {, }]`
-    tokens: Vec<Token>,
-}
-
 impl<'t> ParserInput<'t> {
     /// Generate input from tokens(expect comment and whitespace).
     pub fn new(text: &'t str, raw_tokens: &'t [Token]) -> ParserInput<'t> {
diff --git a/crates/ra_syntax/src/parsing/reparsing.rs b/crates/ra_syntax/src/parsing/reparsing.rs
index ffcb512ad..6957c26c0 100644
--- a/crates/ra_syntax/src/parsing/reparsing.rs
+++ b/crates/ra_syntax/src/parsing/reparsing.rs
@@ -1,11 +1,18 @@
+//! Implementation of incremental re-parsing.
+//!
+//! We use two simple strategies for this:
+//!   - if the edit modifies only a single token (like changing an identifier's
+//!     letter), we replace only this token.
+//!   - otherwise, we search for the nearest `{}` block which contains the edit
+//!     and try to parse only this block.
+
 use ra_text_edit::AtomTextEdit;
 use ra_parser::Reparser;
 
 use crate::{
-    SyntaxKind::*, TextRange, TextUnit,
+    SyntaxKind::*, TextRange, TextUnit, SyntaxError,
     algo,
     syntax_node::{GreenNode, SyntaxNode},
-    syntax_error::SyntaxError,
     parsing::{
         input::ParserInput,
         builder::TreeBuilder,