perf(parser): remove bounds check for getting strings from lexer

Author: camchenry

crates/oxc_parser/src/lexer/string.rs

@@ -255,15 +255,26 @@ impl<'a> Lexer<'a> {
             return self.escaped_strings[&token.start()];
         }
 
-        let raw = &self.source.whole()[token.start() as usize..token.end() as usize];
-        match token.kind() {
+        let start = token.start() as usize;
+        let end = token.end() as usize;
+        let (start, end) = match token.kind() {
             Kind::Str => {
-                &raw[1..raw.len() - 1] // omit surrounding quotes
+                // Omit surrounding quotes
+                (start + 1, end - 1)
             }
             Kind::PrivateIdentifier => {
-                &raw[1..] // omit leading `#`
+                // Omit leading `#`
+                (start + 1, end)
             }
-            _ => raw,
-        }
+            _ => (start, end),
+        };
+        let whole_source = self.source.whole();
+        debug_assert!(start <= whole_source.len());
+        debug_assert!(end <= whole_source.len());
+        debug_assert!(start <= end);
+        debug_assert!(whole_source.is_char_boundary(start));
+        debug_assert!(whole_source.is_char_boundary(end));
+        // SAFETY: `token` is guaranteed to be within the source and on UTF-8 boundaries.
+        unsafe { whole_source.get_unchecked(start..end) }
     }
 }