Merge #1328

1328: Change TokenSource to iteration based r=matklad a=edwin0cheng

This PR change the `TokenSource` trait from random access to be an iteration based trait:
```rust

/// `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!
pub trait TokenSource {
    fn current(&self) -> Token;

    /// Lookahead n token
    fn lookahead_nth(&self, n: usize) -> Token;

    /// bump cursor to next token
    fn bump(&mut self);

    /// Is the current token a specified keyword?
    fn is_keyword(&self, kw: &str) -> bool;
}

/// `TokenCursor` abstracts the cursor of `TokenSource` operates one.
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub struct Token {
    /// What is the current token?
    pub kind: SyntaxKind,

    /// Is the current token joined to the next one (`> >` vs `>>`).
    pub is_jointed_to_next: bool,
}
```

Note that the refactoring based on this new trait will be separated to incoming PRs

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

1 files changed, 2 insertions, 2 deletions

diff --git a/crates/ra_mbe/src/subtree_parser.rs b/crates/ra_mbe/src/subtree_parser.rs
index 709b87a38..9cc989b23 100644
--- a/crates/ra_mbe/src/subtree_parser.rs
+++ b/crates/ra_mbe/src/subtree_parser.rs
@@ -68,13 +68,13 @@ impl<'a> Parser<'a> {
 
     fn parse<F>(self, f: F) -> Option<tt::TokenTree>
     where
-        F: FnOnce(&dyn TokenSource, &mut dyn TreeSink),
+        F: FnOnce(&mut dyn TokenSource, &mut dyn TreeSink),
     {
         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);
+        f(&mut src, &mut sink);
 
         let r = self.finish(sink.token_pos, &mut src);
         if sink.error {