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 <edwin0cheng@gmail.com>
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