4 files changed, 34 insertions, 25 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 13872a3d9..d95e26662 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,6 @@ mod parser;
 
 pub mod syntax_kinds;
 pub use text::{TextUnit, TextRange};
-pub use tree::{SyntaxKind, Token, FileBuilder, File, Node};
+pub use tree::{SyntaxKind, Token, FileBuilder, Sink, File, Node};
 pub use lexer::{next_token, tokenize};
 pub use parser::parse;
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index 7336c5136..0a136266c 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -1,4 +1,4 @@
-use {Token, File, FileBuilder};
+use {Token, File, FileBuilder, Sink};
 
 use syntax_kinds::*;
 
diff --git a/src/tree/file_builder.rs b/src/tree/file_builder.rs
index 430303ce9..eba850fef 100644
--- a/src/tree/file_builder.rs
+++ b/src/tree/file_builder.rs
@@ -1,6 +1,13 @@
 use {SyntaxKind, TextUnit, TextRange};
 use super::{NodeData, NodeIdx, File};
 
+pub trait Sink {
+    fn leaf(&mut self, kind: SyntaxKind, len: TextUnit);
+    fn start_internal(&mut self, kind: SyntaxKind);
+    fn finish_internal(&mut self);
+}
+
+
 pub struct FileBuilder {
     text: String,
     nodes: Vec<NodeData>,
@@ -8,26 +15,8 @@ pub struct FileBuilder {
     pos: TextUnit,
 }
 
-impl FileBuilder {
-    pub fn new(text: String) -> FileBuilder {
-        FileBuilder {
-            text,
-            nodes: Vec::new(),
-            in_progress: Vec::new(),
-            pos: TextUnit::new(0),
-        }
-    }
-
-    pub fn finish(self) -> File {
-        assert!(self.in_progress.is_empty());
-        assert!(self.pos == (self.text.len() as u32).into());
-        File {
-            text: self.text,
-            nodes: self.nodes,
-        }
-    }
-
-    pub fn leaf(&mut self, kind: SyntaxKind, len: TextUnit) {
+impl Sink for FileBuilder {
+    fn leaf(&mut self, kind: SyntaxKind, len: TextUnit) {
         let leaf = NodeData {
             kind,
             range: TextRange::from_len(self.pos, len),
@@ -40,7 +29,7 @@ impl FileBuilder {
         self.add_len(id);
     }
 
-    pub fn start_internal(&mut self, kind: SyntaxKind) {
+    fn start_internal(&mut self, kind: SyntaxKind) {
         let node = NodeData {
             kind,
             range: TextRange::from_len(self.pos, 0.into()),
@@ -56,12 +45,32 @@ impl FileBuilder {
         self.in_progress.push((id, None))
     }
 
-    pub fn finish_internal(&mut self) {
+    fn finish_internal(&mut self) {
         let (id, _) = self.in_progress.pop().unwrap();
         if !self.in_progress.is_empty() {
             self.add_len(id);
         }
     }
+}
+
+impl FileBuilder {
+    pub fn new(text: String) -> FileBuilder {
+        FileBuilder {
+            text,
+            nodes: Vec::new(),
+            in_progress: Vec::new(),
+            pos: TextUnit::new(0),
+        }
+    }
+
+    pub fn finish(self) -> File {
+        assert!(self.in_progress.is_empty());
+        assert!(self.pos == (self.text.len() as u32).into());
+        File {
+            text: self.text,
+            nodes: self.nodes,
+        }
+    }
 
     fn new_node(&mut self, data: NodeData) -> NodeIdx {
         let id = NodeIdx(self.nodes.len() as u32);
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 6bacb46ef..7a5d429a3 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -4,7 +4,7 @@ use syntax_kinds::syntax_info;
 use std::fmt;
 
 mod file_builder;
-pub use self::file_builder::FileBuilder;
+pub use self::file_builder::{FileBuilder, Sink};
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SyntaxKind(pub(crate) u32);