process_edges and expand_var_length carried the expansion budget in the LOOP
condition (`ei < edge_count && *new_count < max_new`). Once new_count reached
max_new they stopped iterating entirely, so match_count was never incremented
for the remaining sources -- even though those sources had real neighbours.
expand_pattern_rels' OPTIONAL fallback is ungated (it has a reserved slot per
binding since the #1177 sizing fix), so it saw match_count == 0 and emitted an
unbound row for every such source.
The result is a false negative that reads as a positive assertion:
MATCH (f:Function) OPTIONAL MATCH (f)-[:CALLS]->(c) WHERE c IS NULL
reports a function as having no callers when it has callers, once an earlier
function in the same scan saturated the budget. That is a dead-code query
telling a user that live code is dead.
The budget caps MATERIALISATION, never detection. Both loops now iterate the
full candidate set, increment match_count whenever a real neighbour passes the
filters, and gate only the write into new_bindings. The bound proof from #1177
is unchanged -- writes are still capped at max_new and fallbacks are still at
most one per binding -- so allocation safety does not depend on this change.
Cost: a saturated source still performs its node lookups and filter checks, the
same ones the unsaturated path performs, and materialises nothing.
Reported by @SEPURI-SAI-KRISHNA while working on the sibling bound-terminal path
in #1378; this is the same defect in expand_pattern_rels, which was already live
on main rather than introduced there.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel
27d9831ab8