1 files changed, 84 insertions, 0 deletions

diff --git a/crates/syntax/src/parsing/text_token_source.rs b/crates/syntax/src/parsing/text_token_source.rs
new file mode 100644
index 000000000..df866dc2b
--- /dev/null
+++ b/crates/syntax/src/parsing/text_token_source.rs
@@ -0,0 +1,84 @@
+//! See `TextTokenSource` docs.
+
+use parser::TokenSource;
+
+use crate::{parsing::lexer::Token, SyntaxKind::EOF, TextRange, TextSize};
+
+/// Implementation of `parser::TokenSource` that takes tokens from source code text.
+pub(crate) struct TextTokenSource<'t> {
+    text: &'t str,
+    /// token and its start position (non-whitespace/comment tokens)
+    /// ```non-rust
+    ///  struct Foo;
+    ///  ^------^--^-
+    ///  |      |    \________
+    ///  |      \____         \
+    ///  |           \         |
+    ///  (struct, 0) (Foo, 7) (;, 10)
+    /// ```
+    /// `[(struct, 0), (Foo, 7), (;, 10)]`
+    token_offset_pairs: Vec<(Token, TextSize)>,
+
+    /// Current token and position
+    curr: (parser::Token, usize),
+}
+
+impl<'t> TokenSource for TextTokenSource<'t> {
+    fn current(&self) -> parser::Token {
+        self.curr.0
+    }
+
+    fn lookahead_nth(&self, n: usize) -> parser::Token {
+        mk_token(self.curr.1 + n, &self.token_offset_pairs)
+    }
+
+    fn bump(&mut self) {
+        if self.curr.0.kind == EOF {
+            return;
+        }
+
+        let pos = self.curr.1 + 1;
+        self.curr = (mk_token(pos, &self.token_offset_pairs), pos);
+    }
+
+    fn is_keyword(&self, kw: &str) -> bool {
+        self.token_offset_pairs
+            .get(self.curr.1)
+            .map(|(token, offset)| &self.text[TextRange::at(*offset, token.len)] == kw)
+            .unwrap_or(false)
+    }
+}
+
+fn mk_token(pos: usize, token_offset_pairs: &[(Token, TextSize)]) -> parser::Token {
+    let (kind, is_jointed_to_next) = match token_offset_pairs.get(pos) {
+        Some((token, offset)) => (
+            token.kind,
+            token_offset_pairs
+                .get(pos + 1)
+                .map(|(_, next_offset)| offset + token.len == *next_offset)
+                .unwrap_or(false),
+        ),
+        None => (EOF, false),
+    };
+    parser::Token { kind, is_jointed_to_next }
+}
+
+impl<'t> TextTokenSource<'t> {
+    /// Generate input from tokens(expect comment and whitespace).
+    pub fn new(text: &'t str, raw_tokens: &'t [Token]) -> TextTokenSource<'t> {
+        let token_offset_pairs: Vec<_> = raw_tokens
+            .iter()
+            .filter_map({
+                let mut len = 0.into();
+                move |token| {
+                    let pair = if token.kind.is_trivia() { None } else { Some((*token, len)) };
+                    len += token.len;
+                    pair
+                }
+            })
+            .collect();
+
+        let first = mk_token(0, &token_offset_pairs);
+        TextTokenSource { text, token_offset_pairs, curr: (first, 0) }
+    }
+}