feat(parser): introduce ParserImpl::token_source method

crates/oxc_parser/src/cursor.rs

@@ -44,12 +44,29 @@ impl<'a> ParserImpl<'a> {
     }
 
     /// Get current source text
+    #[inline]
     pub(crate) fn cur_src(&self) -> &'a str {
-        let range = self.cur_token().span();
-        // SAFETY:
-        // range comes from the lexer, which are ensured to meeting the criteria of `get_unchecked`.
+        self.token_source(&self.token)
+    }
 
-        unsafe { self.source_text.get_unchecked(range.start as usize..range.end as usize) }
+    /// Get source text for a token
+    #[inline]
+    pub(crate) fn token_source(&self, token: &Token) -> &'a str {
+        let span = token.span();
+        if cfg!(debug_assertions) {
+            &self.source_text[span.start as usize..span.end as usize]
+        } else {
+            // SAFETY:
+            // Span comes from the lexer, which ensures:
+            // * `start` and `end` are in bounds of source text.
+            // * `end >= start`.
+            // * `start` and `end` are both on UTF-8 char boundaries.
+            // * `self.source_text` is same text that `Token`s are generated from.
+            //
+            // TODO: I (@overlookmotel) don't think we should really be doing this.
+            // We don't have static guarantees of these properties.
+            unsafe { self.source_text.get_unchecked(span.start as usize..span.end as usize) }
+        }
     }
 
     /// Get current string