Comment

crates/oxc_parser/src/lexer/source.rs

@@ -175,6 +175,11 @@ impl<'a> Source<'a> {
     /// * Moving back `n` bytes would not place current position on a UTF-8 character boundary.
     #[inline]
     pub(super) fn back(&mut self, n: usize) {
+        // This assertion is essential to ensure safety of `read_u8()` call below.
+        // Without this check, calling `back(0)` on an empty `Source` would cause reading
+        // out of bounds.
+        // Compiler should remove this assertion when inlining this function,
+        // as long as it can deduce from calling code that `n` is non-zero.
         assert!(n > 0, "Cannot call `Source::back` with 0");
 
         // Ensure not attempting to go back to before start of source