1 files changed, 49 insertions, 1 deletions

diff --git a/crates/ra_syntax/src/parsing.rs b/crates/ra_syntax/src/parsing.rs
index 761accd7b..6c2c5f78b 100644
--- a/crates/ra_syntax/src/parsing.rs
+++ b/crates/ra_syntax/src/parsing.rs
@@ -8,7 +8,7 @@ mod grammar;
 mod reparsing;
 
 use crate::{
-    SyntaxError,
+    SyntaxError, SyntaxKind, SmolStr,
     parsing::builder::GreenBuilder,
     syntax_node::GreenNode,
 };
@@ -23,3 +23,51 @@ pub(crate) fn parse_text(text: &str) -> (GreenNode, Vec<SyntaxError>) {
         parser_impl::parse_with(GreenBuilder::new(), text, &tokens, grammar::root);
     (green, errors)
 }
+
+/// `TreeSink` abstracts details of a particular syntax tree implementation.
+trait TreeSink {
+    type Tree;
+
+    /// Adds new leaf to the current branch.
+    fn leaf(&mut self, kind: SyntaxKind, text: SmolStr);
+
+    /// Start new branch and make it current.
+    fn start_branch(&mut self, kind: SyntaxKind);
+
+    /// Finish current branch and restore previous
+    /// branch as current.
+    fn finish_branch(&mut self);
+
+    fn error(&mut self, error: SyntaxError);
+
+    /// Complete tree building. Make sure that
+    /// `start_branch` and `finish_branch` calls
+    /// are paired!
+    fn finish(self) -> Self::Tree;
+}
+
+/// `TokenSource` abstracts the source of the tokens parser operates one.
+///
+/// Hopefully this will allow us to treat text and token trees in the same way!
+trait TokenSource {
+    fn token_kind(&self, pos: TokenPos) -> SyntaxKind;
+    fn is_token_joint_to_next(&self, pos: TokenPos) -> bool;
+    fn is_keyword(&self, pos: TokenPos, kw: &str) -> bool;
+}
+
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Default)]
+pub(crate) struct TokenPos(pub u32);
+
+impl std::ops::Add<u32> for TokenPos {
+    type Output = TokenPos;
+
+    fn add(self, rhs: u32) -> TokenPos {
+        TokenPos(self.0 + rhs)
+    }
+}
+
+impl std::ops::AddAssign<u32> for TokenPos {
+    fn add_assign(&mut self, rhs: u32) {
+        self.0 += rhs
+    }
+}