5 files changed, 94 insertions, 86 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 38d3ec7e1..84ce2b783 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -21,6 +21,7 @@ mod mbe_expander;
 mod syntax_bridge;
 mod tt_cursor;
 mod subtree_source;
+mod subtree_parser;
 
 use ra_syntax::SmolStr;
 
diff --git a/crates/ra_mbe/src/subtree_parser.rs b/crates/ra_mbe/src/subtree_parser.rs
new file mode 100644
index 000000000..48eee6fa7
--- /dev/null
+++ b/crates/ra_mbe/src/subtree_parser.rs
@@ -0,0 +1,59 @@
+use crate::subtree_source::SubtreeTokenSource;
+
+use ra_parser::{TokenSource, TreeSink};
+use ra_syntax::{SyntaxKind};
+
+struct OffsetTokenSink {
+    token_pos: usize,
+}
+
+impl TreeSink for OffsetTokenSink {
+    fn token(&mut self, _kind: SyntaxKind, n_tokens: u8) {
+        self.token_pos += n_tokens as usize;
+    }
+    fn start_node(&mut self, _kind: SyntaxKind) {}
+    fn finish_node(&mut self) {}
+    fn error(&mut self, _error: ra_parser::ParseError) {}
+}
+
+pub(crate) struct Parser<'a> {
+    subtree: &'a tt::Subtree,
+    pos: &'a mut usize,
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(pos: &'a mut usize, subtree: &'a tt::Subtree) -> Parser<'a> {
+        Parser { pos, subtree }
+    }
+
+    pub fn parse_path(self) -> Option<tt::TokenTree> {
+        self.parse(ra_parser::parse_path)
+    }
+
+    fn parse<F>(self, f: F) -> Option<tt::TokenTree>
+    where
+        F: FnOnce(&dyn TokenSource, &mut dyn TreeSink),
+    {
+        let mut src = SubtreeTokenSource::new(self.subtree);
+        src.advance(*self.pos, true);
+        let mut sink = OffsetTokenSink { token_pos: 0 };
+
+        f(&src, &mut sink);
+
+        self.finish(sink.token_pos, &mut src)
+    }
+
+    fn finish(self, parsed_token: usize, src: &mut SubtreeTokenSource) -> Option<tt::TokenTree> {
+        let res = src.bump_n(parsed_token, self.pos);
+        let res: Vec<_> = res.into_iter().cloned().collect();
+
+        match res.len() {
+            0 => None,
+            1 => Some(res[0].clone()),
+            _ => Some(tt::TokenTree::Subtree(tt::Subtree {
+                delimiter: tt::Delimiter::None,
+                token_trees: res,
+            })),
+        }
+    }
+}
diff --git a/crates/ra_mbe/src/subtree_source.rs b/crates/ra_mbe/src/subtree_source.rs
index 8f5ce4ed5..d9ba5d3d0 100644
--- a/crates/ra_mbe/src/subtree_source.rs
+++ b/crates/ra_mbe/src/subtree_source.rs
@@ -9,12 +9,12 @@ struct TtToken {
     pub n_tokens: usize,
 }
 
-/// SubtreeSourceQuerier let outside to query internal tokens as string
-pub(crate) struct SubtreeSourceQuerier<'a> {
+/// Querier let outside to query internal tokens as string
+pub(crate) struct Querier<'a> {
     src: &'a SubtreeTokenSource<'a>,
 }
 
-impl<'a> SubtreeSourceQuerier<'a> {
+impl<'a> Querier<'a> {
     pub(crate) fn token(&self, uidx: usize) -> (SyntaxKind, &SmolStr) {
         let tkn = &self.src.tokens[uidx];
         (tkn.kind, &tkn.text)
@@ -32,7 +32,8 @@ impl<'a> SubtreeTokenSource<'a> {
         SubtreeTokenSource { tokens: TtTokenBuilder::build(subtree), tt_pos: 0, subtree }
     }
 
-    pub fn advance(&mut self, curr: usize, skip_first_delimiter: bool) {
+    // Advance token source and skip the first delimiter
+    pub fn advance(&mut self, n_token: usize, skip_first_delimiter: bool) {
         if skip_first_delimiter {
             self.tt_pos += 1;
         }
@@ -47,32 +48,20 @@ impl<'a> SubtreeTokenSource<'a> {
         // Such that we cannot simpliy advance the cursor
         // We have to bump it one by one
         let mut pos = 0;
-        while pos < curr {
+        while pos < n_token {
             pos += self.bump(&self.subtree.token_trees[pos]);
         }
     }
 
-    pub fn querier(&self) -> SubtreeSourceQuerier {
-        SubtreeSourceQuerier { src: self }
-    }
-
-    fn count(&self, tt: &tt::TokenTree) -> usize {
-        assert!(!self.tokens.is_empty());
-        TtTokenBuilder::count_tt_tokens(tt, None)
-    }
-
-    pub(crate) fn bump(&mut self, tt: &tt::TokenTree) -> usize {
-        let cur = &self.tokens[self.tt_pos];
-        let n_tokens = cur.n_tokens;
-        self.tt_pos += self.count(tt);
-        n_tokens
+    pub fn querier(&self) -> Querier {
+        Querier { src: self }
     }
 
     pub(crate) fn bump_n(
         &mut self,
-        n_tokens: usize,
-        mut token_pos: usize,
-    ) -> (usize, Vec<&tt::TokenTree>) {
+        n_tt_tokens: usize,
+        token_pos: &mut usize,
+    ) -> Vec<&tt::TokenTree> {
         let mut res = vec![];
         // Matching `TtToken` cursor to `tt::TokenTree` cursor
         // It is because TtToken is not One to One mapping to tt::Token
@@ -83,17 +72,28 @@ impl<'a> SubtreeTokenSource<'a> {
         //
         // Such that we cannot simpliy advance the cursor
         // We have to bump it one by one
-        let next_pos = self.tt_pos + n_tokens;
-        let old_token_pos = token_pos;
+        let next_pos = self.tt_pos + n_tt_tokens;
 
         while self.tt_pos < next_pos {
-            let current = &self.subtree.token_trees[token_pos];
+            let current = &self.subtree.token_trees[*token_pos];
             let n = self.bump(current);
-            res.extend((0..n).map(|i| &self.subtree.token_trees[token_pos + i]));
-            token_pos += n;
+            res.extend((0..n).map(|i| &self.subtree.token_trees[*token_pos + i]));
+            *token_pos += n;
         }
 
-        (token_pos - old_token_pos, res)
+        res
+    }
+
+    fn count(&self, tt: &tt::TokenTree) -> usize {
+        assert!(!self.tokens.is_empty());
+        TtTokenBuilder::count_tt_tokens(tt, None)
+    }
+
+    fn bump(&mut self, tt: &tt::TokenTree) -> usize {
+        let cur = &self.tokens[self.tt_pos];
+        let n_tokens = cur.n_tokens;
+        self.tt_pos += self.count(tt);
+        n_tokens
     }
 }
 
diff --git a/crates/ra_mbe/src/syntax_bridge.rs b/crates/ra_mbe/src/syntax_bridge.rs
index 102bba341..b0fb91a63 100644
--- a/crates/ra_mbe/src/syntax_bridge.rs
+++ b/crates/ra_mbe/src/syntax_bridge.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     ast, SyntaxKind::*, TextUnit
 };
 
-use crate::subtree_source::{SubtreeTokenSource, SubtreeSourceQuerier};
+use crate::subtree_source::{SubtreeTokenSource, Querier};
 
 /// Maps `tt::TokenId` to the relative range of the original token.
 #[derive(Default)]
@@ -107,14 +107,14 @@ fn convert_tt(
 
 struct TtTreeSink<'a> {
     buf: String,
-    src_querier: SubtreeSourceQuerier<'a>,
+    src_querier: Querier<'a>,
     text_pos: TextUnit,
     token_pos: usize,
     inner: SyntaxTreeBuilder,
 }
 
 impl<'a> TtTreeSink<'a> {
-    fn new(src_querier: SubtreeSourceQuerier<'a>) -> TtTreeSink {
+    fn new(src_querier: Querier<'a>) -> TtTreeSink {
         TtTreeSink {
             buf: String::new(),
             src_querier,
diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
index 52e072599..d29faa77c 100644
--- a/crates/ra_mbe/src/tt_cursor.rs
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -1,25 +1,5 @@
 use crate::ParseError;
-use crate::subtree_source::SubtreeTokenSource;
-
-use ra_parser::{TokenSource, TreeSink};
-
-use ra_syntax::{
-    SyntaxKind
-};
-
-struct SubtreeTokenSink {
-    token_pos: usize,
-}
-
-impl TreeSink for SubtreeTokenSink {
-    fn token(&mut self, _kind: SyntaxKind, n_tokens: u8) {
-        self.token_pos += n_tokens as usize;
-    }
-
-    fn start_node(&mut self, _kind: SyntaxKind) {}
-    fn finish_node(&mut self) {}
-    fn error(&mut self, _error: ra_parser::ParseError) {}
-}
+use crate::subtree_parser::Parser;
 
 #[derive(Clone)]
 pub(crate) struct TtCursor<'a> {
@@ -99,41 +79,9 @@ impl<'a> TtCursor<'a> {
         })
     }
 
-    fn eat_parse_result(
-        &mut self,
-        parsed_token: usize,
-        src: &mut SubtreeTokenSource,
-    ) -> Option<tt::TokenTree> {
-        let (adv, res) = src.bump_n(parsed_token, self.pos);
-        self.pos += adv;
-
-        let res: Vec<_> = res.into_iter().cloned().collect();
-
-        match res.len() {
-            0 => None,
-            1 => Some(res[0].clone()),
-            _ => Some(tt::TokenTree::Subtree(tt::Subtree {
-                delimiter: tt::Delimiter::None,
-                token_trees: res,
-            })),
-        }
-    }
-
-    fn eat_parse<F>(&mut self, f: F) -> Option<tt::TokenTree>
-    where
-        F: FnOnce(&dyn TokenSource, &mut dyn TreeSink),
-    {
-        let mut src = SubtreeTokenSource::new(self.subtree);
-        src.advance(self.pos, true);
-        let mut sink = SubtreeTokenSink { token_pos: 0 };
-
-        f(&src, &mut sink);
-
-        self.eat_parse_result(sink.token_pos, &mut src)
-    }
-
     pub(crate) fn eat_path(&mut self) -> Option<tt::TokenTree> {
-        self.eat_parse(ra_parser::parse_path)
+        let parser = Parser::new(&mut self.pos, self.subtree);
+        parser.parse_path()
     }
 
     pub(crate) fn expect_char(&mut self, char: char) -> Result<(), ParseError> {