iffyio commented on code in PR #2352:
URL:
https://github.com/apache/datafusion-sqlparser-rs/pull/2352#discussion_r3310342696
##########
src/parser/mod.rs:
##########
@@ -1717,6 +1731,23 @@ impl<'a> Parser<'a> {
return prefix;
}
+ // Memoize parse_prefix failures to break 2^N speculation when both
+ // prefix arms fail at every level (e.g. `IF(current_time(...x`).
+ // The per-arm cache in `parse_prefix_inner` complements this for
+ // chains where the reserved arm fails but the unreserved fallback
+ // succeeds (e.g. `case-case-...c`).
+ let start_index = self.index;
+ if let Some(cached) = self.failed_prefix_positions.get(&start_index) {
+ return Err(cached.clone());
+ }
+ let result = self.parse_prefix_inner();
+ if let Err(ref e) = result {
+ self.failed_prefix_positions.insert(start_index, e.clone());
Review Comment:
wondering about memory usage, how large do we expect the caches to get in
the worse case scenarios?
##########
src/parser/mod.rs:
##########
@@ -1801,7 +1832,21 @@ impl<'a> Parser<'a> {
// We first try to parse the word and following tokens as a
special expression, and if that fails,
// we rollback and try to parse it as an identifier.
let w = w.clone();
- match self.try_parse(|parser|
parser.parse_expr_prefix_by_reserved_word(&w, span)) {
+ // Memoize failed speculative reserved-word parses. When
+ // the reserved arm (CASE, CURRENT_TIME, etc.) does
+ // exponential work but the unreserved fallback ultimately
+ // succeeds, the overall `parse_prefix` returns `Ok` and the
+ // outer cache never fires. Chains like `case-case-...c`
+ // need this per-arm cache to break the doubling.
Review Comment:
I wasn't able to follow this comment, what is 'outer cache' and 'break
doubling' referring to?
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