2 files changed, 72 insertions, 2 deletions

diff --git a/src/tree/file_builder.rs b/src/tree/file_builder.rs
index 712602168..4983006cd 100644
--- a/src/tree/file_builder.rs
+++ b/src/tree/file_builder.rs
@@ -7,8 +7,13 @@
 //! tree builder: the parser produces a stream of events like
 //! `start node`, `finish node`, and `FileBuilder` converts
 //! this stream to a real tree.
-use {SyntaxKind, TextRange, TextUnit};
+use std::sync::Arc;
+use {
+    SyntaxKind, TextRange, TextUnit,
+    yellow::GreenNode
+};
 use super::{File, NodeData, NodeIdx, SyntaxErrorData};
+use SError;
 
 pub(crate) trait Sink {
     fn leaf(&mut self, kind: SyntaxKind, len: TextUnit);
@@ -159,3 +164,68 @@ fn grow(left: &mut TextRange, right: TextRange) {
 pub(crate) struct ErrorMsg {
     pub(crate) msg: String,
 }
+
+pub(crate) struct GreenBuilder {
+    text: String,
+    stack: Vec<GreenNode>,
+    pos: TextUnit,
+    root: Option<GreenNode>,
+    errors: Vec<SError>,
+}
+
+impl GreenBuilder {
+    pub(crate) fn new(text: String) -> GreenBuilder {
+        GreenBuilder {
+            text,
+            stack: Vec::new(),
+            pos: 0.into(),
+            root: None,
+            errors: Vec::new(),
+        }
+    }
+
+    pub(crate) fn finish(self) -> (GreenNode, Vec<SError>) {
+        (self.root.unwrap(), self.errors)
+    }
+}
+
+impl Sink for GreenBuilder {
+    fn leaf(&mut self, kind: SyntaxKind, len: TextUnit) {
+        let range = TextRange::offset_len(self.pos, len);
+        self.pos += len;
+        let text = self.text[range].to_owned();
+        let parent = self.stack.last_mut().unwrap();
+        if kind.is_trivia() {
+            parent.push_trivia(kind, text);
+        } else {
+            let node = GreenNode::new_leaf(kind, text);
+            parent.push_child(Arc::new(node));
+        }
+    }
+
+    fn start_internal(&mut self, kind: SyntaxKind) {
+        self.stack.push(GreenNode::new_branch(kind))
+    }
+
+    fn finish_internal(&mut self) {
+        let node = self.stack.pop().unwrap();
+        if let Some(parent) = self.stack.last_mut() {
+            parent.push_child(Arc::new(node))
+        } else {
+            self.root = Some(node);
+        }
+    }
+
+    fn error(&mut self, err: ErrorMsg) {
+        self.errors.push(SError { message: err.msg, offset: self.pos })
+    }
+}
+impl SyntaxKind {
+    fn is_trivia(self) -> bool {
+        match self {
+            SyntaxKind::WHITESPACE | SyntaxKind::DOC_COMMENT | SyntaxKind::COMMENT => true,
+            _ => false
+        }
+    }
+}
+
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index f7b16d7b5..7abe17592 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -2,7 +2,7 @@ mod file_builder;
 
 use ::{TextRange, TextUnit};
 use std::{fmt, cmp};
-pub(crate) use self::file_builder::{ErrorMsg, FileBuilder, Sink};
+pub(crate) use self::file_builder::{ErrorMsg, FileBuilder, Sink, GreenBuilder};
 
 pub use syntax_kinds::SyntaxKind;