Merge #1312

1312: Introduce TokenBuffer r=matklad a=edwin0cheng

As discussed in Zulip, this PR Introduce `TokenBuffer` , a safe version of  `syn` crate `TokenBuffer` which support cursor based traversal of `tt::TokenTree`. This is the basis of incoming refactoring of `TokenSource` iterator based API.

This PR do the following things:

* Add TokenBuffer in `ra_tt` crate.
* Try to use this new API to refactor the `SubtreeSource` to prove it usage.




Co-authored-by: Edwin Cheng <[email protected]>

5 files changed, 259 insertions, 201 deletions

diff --git a/crates/ra_mbe/src/subtree_parser.rs b/crates/ra_mbe/src/subtree_parser.rs
index f07107414..709b87a38 100644
--- a/crates/ra_mbe/src/subtree_parser.rs
+++ b/crates/ra_mbe/src/subtree_parser.rs
@@ -2,6 +2,7 @@ use crate::subtree_source::SubtreeTokenSource;
 
 use ra_parser::{TokenSource, TreeSink};
 use ra_syntax::{SyntaxKind};
+use tt::buffer::TokenBuffer;
 
 struct OffsetTokenSink {
     token_pos: usize,
@@ -69,7 +70,8 @@ impl<'a> Parser<'a> {
     where
         F: FnOnce(&dyn TokenSource, &mut dyn TreeSink),
     {
-        let mut src = SubtreeTokenSource::new(&self.subtree.token_trees[*self.cur_pos..]);
+        let buffer = TokenBuffer::new(&self.subtree.token_trees[*self.cur_pos..]);
+        let mut src = SubtreeTokenSource::new(&buffer);
         let mut sink = OffsetTokenSink { token_pos: 0, error: false };
 
         f(&src, &mut sink);
@@ -85,7 +87,7 @@ impl<'a> Parser<'a> {
         let res = src.bump_n(parsed_token);
         *self.cur_pos += res.len();
 
-        let res: Vec<_> = res.into_iter().cloned().collect();
+        let res: Vec<_> = res.into_iter().collect();
 
         match res.len() {
             0 => None,
diff --git a/crates/ra_mbe/src/subtree_source.rs b/crates/ra_mbe/src/subtree_source.rs
index c938acf64..972af4a7c 100644
--- a/crates/ra_mbe/src/subtree_source.rs
+++ b/crates/ra_mbe/src/subtree_source.rs
@@ -1,50 +1,10 @@
 use ra_parser::{TokenSource};
 use ra_syntax::{classify_literal, SmolStr, SyntaxKind, SyntaxKind::*, T};
-use std::cell::{RefCell};
+use std::cell::{RefCell, Cell};
+use tt::buffer::{TokenBuffer, Cursor};
 
-// A Sequece of Token,
-#[derive(Debug, Clone, Eq, PartialEq)]
-pub(super) enum TokenSeq<'a> {
-    Subtree(&'a tt::Subtree),
-    Seq(&'a [tt::TokenTree]),
-}
-
-impl<'a> From<&'a tt::Subtree> for TokenSeq<'a> {
-    fn from(s: &'a tt::Subtree) -> TokenSeq<'a> {
-        TokenSeq::Subtree(s)
-    }
-}
-
-impl<'a> From<&'a [tt::TokenTree]> for TokenSeq<'a> {
-    fn from(s: &'a [tt::TokenTree]) -> TokenSeq<'a> {
-        TokenSeq::Seq(s)
-    }
-}
-
-#[derive(Debug)]
-enum DelimToken<'a> {
-    Delim(&'a tt::Delimiter, bool),
-    Token(&'a tt::TokenTree),
-    End,
-}
-
-impl<'a> TokenSeq<'a> {
-    fn get(&self, pos: usize) -> DelimToken<'a> {
-        match self {
-            TokenSeq::Subtree(subtree) => {
-                let len = subtree.token_trees.len() + 2;
-                match pos {
-                    p if p >= len => DelimToken::End,
-                    p if p == len - 1 => DelimToken::Delim(&subtree.delimiter, true),
-                    0 => DelimToken::Delim(&subtree.delimiter, false),
-                    p => DelimToken::Token(&subtree.token_trees[p - 1]),
-                }
-            }
-            TokenSeq::Seq(tokens) => {
-                tokens.get(pos).map(DelimToken::Token).unwrap_or(DelimToken::End)
-            }
-        }
-    }
+pub(crate) trait Querier {
+    fn token(&self, uidx: usize) -> (SyntaxKind, SmolStr, bool);
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -54,183 +14,101 @@ struct TtToken {
     pub text: SmolStr,
 }
 
-#[derive(Debug, Clone, Eq, PartialEq)]
-enum WalkCursor {
-    Token(usize, TtToken),
-    Eof,
-}
-
-#[derive(Debug)]
-struct SubTreeWalker<'a> {
-    pos: usize,
-    stack: Vec<(TokenSeq<'a>, usize)>,
-    cursor: WalkCursor,
-    ts: TokenSeq<'a>,
-}
-
-impl<'a> SubTreeWalker<'a> {
-    fn new(ts: TokenSeq<'a>) -> SubTreeWalker {
-        let mut res = SubTreeWalker { pos: 0, stack: vec![], cursor: WalkCursor::Eof, ts };
-
-        res.reset();
-        res
-    }
-
-    fn is_eof(&self) -> bool {
-        self.cursor == WalkCursor::Eof
-    }
-
-    fn reset(&mut self) {
-        self.pos = 0;
-        self.stack = vec![];
-
-        self.cursor = match self.ts.get(0) {
-            DelimToken::Token(token) => match token {
-                tt::TokenTree::Subtree(subtree) => {
-                    let ts = TokenSeq::from(subtree);
-                    self.stack.push((ts, 0));
-                    WalkCursor::Token(0, convert_delim(subtree.delimiter, false))
-                }
-                tt::TokenTree::Leaf(leaf) => WalkCursor::Token(0, convert_leaf(leaf)),
-            },
-            DelimToken::Delim(delim, is_end) => {
-                assert!(!is_end);
-                WalkCursor::Token(0, convert_delim(*delim, false))
-            }
-            DelimToken::End => WalkCursor::Eof,
-        }
-    }
-
-    fn current(&self) -> Option<&TtToken> {
-        match &self.cursor {
-            WalkCursor::Token(_, t) => Some(t),
-            WalkCursor::Eof => None,
-        }
-    }
-
-    fn top(&self) -> &TokenSeq {
-        self.stack.last().map(|(t, _)| t).unwrap_or(&self.ts)
-    }
-
-    /// Move cursor forward by 1 step        
-    fn forward(&mut self) {
-        if self.is_eof() {
-            return;
-        }
-        self.pos += 1;
-
-        if let WalkCursor::Token(u, _) = self.cursor {
-            self.cursor = self.walk_token(u)
-        }
-    }
-
-    /// Traversal child token
-    fn walk_token(&mut self, pos: usize) -> WalkCursor {
-        let top = self.stack.last().map(|(t, _)| t).unwrap_or(&self.ts);
-        let pos = pos + 1;
-
-        match top.get(pos) {
-            DelimToken::Token(token) => match token {
-                tt::TokenTree::Subtree(subtree) => {
-                    let ts = TokenSeq::from(subtree);
-                    self.stack.push((ts, pos));
-                    WalkCursor::Token(0, convert_delim(subtree.delimiter, false))
-                }
-                tt::TokenTree::Leaf(leaf) => WalkCursor::Token(pos, convert_leaf(leaf)),
-            },
-            DelimToken::Delim(delim, is_end) => {
-                WalkCursor::Token(pos, convert_delim(*delim, is_end))
-            }
-            DelimToken::End => {
-                // it is the top level
-                if let Some((_, last_idx)) = self.stack.pop() {
-                    self.walk_token(last_idx)
-                } else {
-                    WalkCursor::Eof
-                }
-            }
-        }
-    }
-}
-
-pub(crate) trait Querier {
-    fn token(&self, uidx: usize) -> (SyntaxKind, SmolStr, bool);
-}
-
 // A wrapper class for ref cell
 #[derive(Debug)]
-pub(crate) struct WalkerOwner<'a> {
-    walker: RefCell<SubTreeWalker<'a>>,
+pub(crate) struct SubtreeWalk<'a> {
+    start: Cursor<'a>,
+    cursor: Cell<Cursor<'a>>,
     cached: RefCell<Vec<Option<TtToken>>>,
 }
 
-impl<'a> WalkerOwner<'a> {
-    fn new<I: Into<TokenSeq<'a>>>(ts: I) -> Self {
-        WalkerOwner {
-            walker: RefCell::new(SubTreeWalker::new(ts.into())),
+impl<'a> SubtreeWalk<'a> {
+    fn new(cursor: Cursor<'a>) -> Self {
+        SubtreeWalk {
+            start: cursor,
+            cursor: Cell::new(cursor),
             cached: RefCell::new(Vec::with_capacity(10)),
         }
     }
 
-    fn get<'b>(&self, pos: usize) -> Option<TtToken> {
+    fn get(&self, pos: usize) -> Option<TtToken> {
         let mut cached = self.cached.borrow_mut();
         if pos < cached.len() {
             return cached[pos].clone();
         }
 
         while pos >= cached.len() {
-            self.set_pos(cached.len());
-            let walker = self.walker.borrow();
-            cached.push(walker.current().cloned());
+            let cursor = self.cursor.get();
+            if cursor.eof() {
+                cached.push(None);
+                continue;
+            }
+
+            match cursor.token_tree() {
+                Some(tt::TokenTree::Leaf(leaf)) => {
+                    cached.push(Some(convert_leaf(&leaf)));
+                    self.cursor.set(cursor.bump());
+                }
+                Some(tt::TokenTree::Subtree(subtree)) => {
+                    self.cursor.set(cursor.subtree().unwrap());
+                    cached.push(Some(convert_delim(subtree.delimiter, false)));
+                }
+                None => {
+                    if let Some(subtree) = cursor.end() {
+                        cached.push(Some(convert_delim(subtree.delimiter, true)));
+                        self.cursor.set(cursor.bump());
+                    }
+                }
+            }
         }
 
         return cached[pos].clone();
     }
 
-    fn set_pos(&self, pos: usize) {
-        let mut walker = self.walker.borrow_mut();
-        assert!(walker.pos <= pos);
+    fn collect_token_trees(&mut self, n: usize) -> Vec<tt::TokenTree> {
+        let mut res = vec![];
 
-        while pos > walker.pos && !walker.is_eof() {
-            walker.forward();
-        }
-    }
+        let mut pos = 0;
+        let mut cursor = self.start;
+        let mut level = 0;
 
-    fn collect_token_trees(&mut self, n: usize) -> Vec<&tt::TokenTree> {
-        let mut res = vec![];
-        let mut walker = self.walker.borrow_mut();
-        walker.reset();
+        while pos < n {
+            if cursor.eof() {
+                break;
+            }
 
-        while walker.pos < n {
-            if let WalkCursor::Token(u, _) = &walker.cursor {
-                // We only collect the topmost child
-                if walker.stack.len() == 0 {
-                    if let DelimToken::Token(token) = walker.ts.get(*u) {
-                        res.push(token);
+            match cursor.token_tree() {
+                Some(tt::TokenTree::Leaf(leaf)) => {
+                    if level == 0 {
+                        res.push(leaf.into());
                     }
+                    cursor = cursor.bump();
+                    pos += 1;
                 }
-                // Check whether the second level is a subtree
-                // if so, collect its parent which is topmost child
-                else if walker.stack.len() == 1 {
-                    if let DelimToken::Delim(_, is_end) = walker.top().get(*u) {
-                        if !is_end {
-                            let (_, last_idx) = &walker.stack[0];
-                            if let DelimToken::Token(token) = walker.ts.get(*last_idx) {
-                                res.push(token);
-                            }
-                        }
+                Some(tt::TokenTree::Subtree(subtree)) => {
+                    if level == 0 {
+                        res.push(subtree.into());
                     }
+                    pos += 1;
+                    level += 1;
+                    cursor = cursor.subtree().unwrap();
                 }
-            }
 
-            walker.forward();
+                None => {
+                    if let Some(_) = cursor.end() {
+                        level -= 1;
+                        pos += 1;
+                        cursor = cursor.bump();
+                    }
+                }
+            }
         }
 
         res
     }
 }
 
-impl<'a> Querier for WalkerOwner<'a> {
+impl<'a> Querier for SubtreeWalk<'a> {
     fn token(&self, uidx: usize) -> (SyntaxKind, SmolStr, bool) {
         self.get(uidx)
             .map(|tkn| (tkn.kind, tkn.text, tkn.is_joint_to_next))
@@ -239,22 +117,22 @@ impl<'a> Querier for WalkerOwner<'a> {
 }
 
 pub(crate) struct SubtreeTokenSource<'a> {
-    walker: WalkerOwner<'a>,
+    walker: SubtreeWalk<'a>,
 }
 
 impl<'a> SubtreeTokenSource<'a> {
-    pub fn new<I: Into<TokenSeq<'a>>>(ts: I) -> SubtreeTokenSource<'a> {
-        SubtreeTokenSource { walker: WalkerOwner::new(ts) }
+    pub fn new(buffer: &'a TokenBuffer) -> SubtreeTokenSource<'a> {
+        SubtreeTokenSource { walker: SubtreeWalk::new(buffer.begin()) }
     }
 
-    pub fn querier<'b>(&'a self) -> &'b WalkerOwner<'a>
+    pub fn querier<'b>(&'a self) -> &'b SubtreeWalk<'a>
     where
         'a: 'b,
     {
         &self.walker
     }
 
-    pub(crate) fn bump_n(&mut self, parsed_tokens: usize) -> Vec<&tt::TokenTree> {
+    pub(crate) fn bump_n(&mut self, parsed_tokens: usize) -> Vec<tt::TokenTree> {
         let res = self.walker.collect_token_trees(parsed_tokens);
         res
     }
diff --git a/crates/ra_mbe/src/syntax_bridge.rs b/crates/ra_mbe/src/syntax_bridge.rs
index d8e344557..0a75305b4 100644
--- a/crates/ra_mbe/src/syntax_bridge.rs
+++ b/crates/ra_mbe/src/syntax_bridge.rs
@@ -47,7 +47,8 @@ pub fn syntax_node_to_token_tree(node: &SyntaxNode) -> Option<(tt::Subtree, Toke
 
 /// Parses the token tree (result of macro expansion) to an expression
 pub fn token_tree_to_expr(tt: &tt::Subtree) -> Result<TreeArc<ast::Expr>, ExpandError> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse_expr(&token_source, &mut tree_sink);
     if tree_sink.roots.len() != 1 {
@@ -62,7 +63,8 @@ pub fn token_tree_to_expr(tt: &tt::Subtree) -> Result<TreeArc<ast::Expr>, Expand
 
 /// Parses the token tree (result of macro expansion) to a Pattern
 pub fn token_tree_to_pat(tt: &tt::Subtree) -> Result<TreeArc<ast::Pat>, ExpandError> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse_pat(&token_source, &mut tree_sink);
     if tree_sink.roots.len() != 1 {
@@ -75,7 +77,8 @@ pub fn token_tree_to_pat(tt: &tt::Subtree) -> Result<TreeArc<ast::Pat>, ExpandEr
 
 /// Parses the token tree (result of macro expansion) to a Type
 pub fn token_tree_to_ty(tt: &tt::Subtree) -> Result<TreeArc<ast::TypeRef>, ExpandError> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse_ty(&token_source, &mut tree_sink);
     if tree_sink.roots.len() != 1 {
@@ -89,7 +92,8 @@ pub fn token_tree_to_ty(tt: &tt::Subtree) -> Result<TreeArc<ast::TypeRef>, Expan
 pub fn token_tree_to_macro_stmts(
     tt: &tt::Subtree,
 ) -> Result<TreeArc<ast::MacroStmts>, ExpandError> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse_macro_stmts(&token_source, &mut tree_sink);
     if tree_sink.roots.len() != 1 {
@@ -103,7 +107,8 @@ pub fn token_tree_to_macro_stmts(
 pub fn token_tree_to_macro_items(
     tt: &tt::Subtree,
 ) -> Result<TreeArc<ast::MacroItems>, ExpandError> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse_macro_items(&token_source, &mut tree_sink);
     if tree_sink.roots.len() != 1 {
@@ -115,7 +120,8 @@ pub fn token_tree_to_macro_items(
 
 /// Parses the token tree (result of macro expansion) as a sequence of items
 pub fn token_tree_to_ast_item_list(tt: &tt::Subtree) -> TreeArc<ast::SourceFile> {
-    let token_source = SubtreeTokenSource::new(tt);
+    let buffer = tt::buffer::TokenBuffer::new(&[tt.clone().into()]);
+    let token_source = SubtreeTokenSource::new(&buffer);
     let mut tree_sink = TtTreeSink::new(token_source.querier());
     ra_parser::parse(&token_source, &mut tree_sink);
     let syntax = tree_sink.inner.finish();
@@ -381,7 +387,8 @@ mod tests {
             "#,
         );
         let expansion = expand(&rules, "literals!(foo)");
-        let tt_src = SubtreeTokenSource::new(&expansion);
+        let buffer = tt::buffer::TokenBuffer::new(&[expansion.clone().into()]);
+        let tt_src = SubtreeTokenSource::new(&buffer);
 
         let query = tt_src.querier();
 
diff --git a/crates/ra_tt/src/buffer.rs b/crates/ra_tt/src/buffer.rs
new file mode 100644
index 000000000..56b844b8b
--- /dev/null
+++ b/crates/ra_tt/src/buffer.rs
@@ -0,0 +1,169 @@
+use crate::{TokenTree, Subtree, Leaf};
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+struct EntryId(usize);
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+struct EntryPtr(EntryId, usize);
+
+/// Internal type which is used instead of `TokenTree` to represent a token tree
+/// within a `TokenBuffer`.
+#[derive(Debug)]
+enum Entry {
+    // Mimicking types from proc-macro.
+    Subtree(Subtree, EntryId),
+    Leaf(Leaf),
+    // End entries contain a pointer to the entry from the containing
+    // token tree, or None if this is the outermost level.
+    End(Option<EntryPtr>),
+}
+
+/// A token tree buffer
+/// The safe version of `syn` [`TokenBuffer`](https://github.com/dtolnay/syn/blob/6533607f91686545cb034d2838beea338d9d0742/src/buffer.rs#L41)
+#[derive(Debug)]
+pub struct TokenBuffer {
+    buffers: Vec<Box<[Entry]>>,
+}
+
+impl TokenBuffer {
+    pub fn new(tokens: &[TokenTree]) -> TokenBuffer {
+        let mut buffers = vec![];
+
+        let idx = TokenBuffer::new_inner(tokens, &mut buffers, None);
+        assert_eq!(idx, 0);
+
+        TokenBuffer { buffers }
+    }
+
+    fn new_inner(
+        tokens: &[TokenTree],
+        buffers: &mut Vec<Box<[Entry]>>,
+        next: Option<EntryPtr>,
+    ) -> usize {
+        let mut entries = vec![];
+        let mut children = vec![];
+
+        for (idx, tt) in tokens.iter().cloned().enumerate() {
+            match tt {
+                TokenTree::Leaf(leaf) => {
+                    entries.push(Entry::Leaf(leaf));
+                }
+                TokenTree::Subtree(subtree) => {
+                    entries.push(Entry::End(None));
+                    children.push((idx, subtree));
+                }
+            }
+        }
+
+        entries.push(Entry::End(next));
+        let res = buffers.len();
+        buffers.push(entries.into_boxed_slice());
+
+        for (child_idx, subtree) in children {
+            let idx = TokenBuffer::new_inner(
+                &subtree.token_trees,
+                buffers,
+                Some(EntryPtr(EntryId(res), child_idx + 1)),
+            );
+            buffers[res].as_mut()[child_idx] = Entry::Subtree(subtree, EntryId(idx));
+        }
+
+        res
+    }
+
+    /// Creates a cursor referencing the first token in the buffer and able to
+    /// traverse until the end of the buffer.
+    pub fn begin(&self) -> Cursor {
+        Cursor::create(self, EntryPtr(EntryId(0), 0))
+    }
+
+    fn entry(&self, ptr: &EntryPtr) -> Option<&Entry> {
+        let id = ptr.0;
+        self.buffers[id.0].get(ptr.1)
+    }
+}
+
+/// A safe version of `Cursor` from `syn` crate https://github.com/dtolnay/syn/blob/6533607f91686545cb034d2838beea338d9d0742/src/buffer.rs#L125
+#[derive(Copy, Clone, Debug)]
+pub struct Cursor<'a> {
+    buffer: &'a TokenBuffer,
+    ptr: EntryPtr,
+}
+
+impl<'a> PartialEq for Cursor<'a> {
+    fn eq(&self, other: &Cursor) -> bool {
+        self.ptr == other.ptr && std::ptr::eq(self.buffer, other.buffer)
+    }
+}
+
+impl<'a> Eq for Cursor<'a> {}
+
+impl<'a> Cursor<'a> {
+    /// Check whether it is eof
+    pub fn eof(self) -> bool {
+        match self.buffer.entry(&self.ptr) {
+            None | Some(Entry::End(None)) => true,
+            _ => false,
+        }
+    }
+
+    /// If the cursor is pointing at the end of a subtree, returns
+    /// the parent subtree
+    pub fn end(self) -> Option<(&'a Subtree)> {
+        match self.entry() {
+            Some(Entry::End(Some(ptr))) => {
+                let idx = ptr.1;
+                if let Some(Entry::Subtree(subtree, _)) =
+                    self.buffer.entry(&EntryPtr(ptr.0, idx - 1))
+                {
+                    return Some(subtree);
+                }
+
+                None
+            }
+            _ => None,
+        }
+    }
+
+    fn entry(self) -> Option<(&'a Entry)> {
+        self.buffer.entry(&self.ptr)
+    }
+
+    /// If the cursor is pointing at a `Subtree`, returns
+    /// a cursor into that subtree
+    pub fn subtree(self) -> Option<Cursor<'a>> {
+        match self.entry() {
+            Some(Entry::Subtree(_, entry_id)) => {
+                Some(Cursor::create(self.buffer, EntryPtr(*entry_id, 0)))
+            }
+            _ => None,
+        }
+    }
+
+    /// If the cursor is pointing at a `TokenTree`, returns it
+    pub fn token_tree(self) -> Option<(TokenTree)> {
+        match self.entry() {
+            Some(Entry::Leaf(leaf)) => Some(leaf.clone().into()),
+            Some(Entry::Subtree(subtree, _)) => Some(subtree.clone().into()),
+            Some(Entry::End(_)) => None,
+            None => None,
+        }
+    }
+
+    fn create(buffer: &'a TokenBuffer, ptr: EntryPtr) -> Cursor<'a> {
+        Cursor { buffer, ptr }
+    }
+
+    /// Bump the cursor
+    pub fn bump(self) -> Cursor<'a> {
+        if let Some(Entry::End(exit)) = self.buffer.entry(&self.ptr) {
+            if let Some(exit) = exit {
+                Cursor::create(self.buffer, *exit)
+            } else {
+                self
+            }
+        } else {
+            Cursor::create(self.buffer, EntryPtr(self.ptr.0, self.ptr.1 + 1))
+        }
+    }
+}
diff --git a/crates/ra_tt/src/lib.rs b/crates/ra_tt/src/lib.rs
index 62c5ac52a..2a48c66c4 100644
--- a/crates/ra_tt/src/lib.rs
+++ b/crates/ra_tt/src/lib.rs
@@ -165,3 +165,5 @@ impl Subtree {
         self.token_trees.len() + children_count
     }
 }
+
+pub mod buffer;