parser: reject IN without a parenthesised list/subquery (was silently dropped)#48
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… dropped) `IN` must be followed by a parenthesised value list or subquery. When it was not - e.g. `WHERE a IN 5` - the parser left `in_operand` null, hit the "neither list nor subquery" fallback, and `continue`d without building an InExpr: the IN was swallowed and the predicate degraded to its bare left operand `a`. That is a silent wrong result - the filter effectively vanished and the query would return all rows. Error out when IN is not followed by `(`, instead of dropping it. The valid parenthesised list and subquery forms (and NOT IN) are unchanged. Tests (test_parser_expr_hardening): `a IN 5` / `a NOT IN 5` are rejected; `a IN (1,2,3)`, `a IN (SELECT ...)`, and `a NOT IN (1,2)` still parse to InExpr. Full suite 37/37 green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01FyKDAbMWGwiZq4iJx3imsg
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What
WHERE a IN 5(anINnot followed by parentheses) silently dropped the predicate: the parser leftin_operandnull, hit the "neither list nor subquery" fallback, andcontinued without building anInExpr, so the predicate degraded to its bare left operanda. TheWHEREeffectively vanished — a silent wrong result that would return all rows.How
INmust be followed by a parenthesised value list or subquery. Error when it isn't, instead of dropping it. The valid forms are untouched.Before / after
WHERE a IN 5— before:WhereClause → ColumnRef('a')(theIN 5gone, 1 trailing token); after:PARSE ERROR: expected '(' with a value list or subquery after IN.Tests
test_parser_expr_hardening:a IN 5/a NOT IN 5rejected;a IN (1,2,3),a IN (SELECT …),a NOT IN (1,2)still parse toInExpr(regression guard). Full suite 37/37 green.Part of the parser-layer robustness pass (CASE #46 and
IS DISTINCT FROM#47 merged; the set-operation drops follow).