LucaCappelletti94 commented on code in PR #2400:
URL:
https://github.com/apache/datafusion-sqlparser-rs/pull/2400#discussion_r4423955369
##########
src/ast/spans.rs:
##########
@@ -3423,4 +3431,48 @@ SETTINGS update_parallel_mode = 'auto'"#;
assert_eq!(test.get_source(expr.span()), expected, "{sql}");
}
}
+
+ #[test]
+ #[cfg(feature = "recursive-protection")]
+ fn test_deeply_nested_expr_span_does_not_overflow() {
+ // 200k nested nodes on a 512 KiB stack overflow unless the walk grows
the stack.
+ std::thread::Builder::new()
+ .stack_size(512 * 1024)
+ .spawn(|| {
+ let mut expr = Expr::Identifier(crate::ast::Ident::new("x"));
+ for _ in 0..200_000 {
+ expr = Expr::Nested(Box::new(expr));
+ }
+ let _ = expr.span();
+ // Dropping the chain recurses too; leak it so the test
measures only the span walk.
Review Comment:
Dropping a deep `OR` chain recurses too, but its frames are far smaller than
those of `span()`. On a 2 MiB thread in release, `span()` on main overflows at
about 2,400 `OR` terms, while dropping the same tree only overflows at about
32,000. In debug the figures are 313 against about 21,000. Of course all of
these inputs are only adversarial stuff.
I agree with you that a different representation is the long term solution,
and I think it is also worth adding that most of the spans current
implementations are different flavours of wrong, so a refactoring regarding
them will need to take place at some point in the future.
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