execExprInterp IS_UPDATEXML: NULL arguments crash; missing hook returns Datum 0 as non-null

[Aias00]

Bug Report

IvorySQL Version

master at c3529ba4789ee220caefc858e58bbe6f1563ad14

Current Behavior

src/backend/executor/execExprInterp.c (IS_UPDATEXML case, lines 4741-4752):

1. NULL arguments crash (high): the argument list is built with DatumGetPointer(argvalue[i]) without checking op->d.xmlexpr.argnull[i]. A NULL argument (NULL column or NULL subexpression) leaves argvalue[i] as uninitialized garbage, and the updatexml() hook dereferences it — backend crash. The sibling IS_XMLSERIALIZE / IS_DOCUMENT cases check argnull[0] first.

2. Missing-hook fallback returns a non-null Datum 0 (medium): when ora_updatexml_hook is NULL (extension not loaded / stale plan), the else branch sets *op->resvalue = (Datum) 0; *op->resnull = false; — a "non-null" zero Datum that downstream code treats as a valid text pointer.

Expected behavior/code

• Skip (return with resnull already true) when any argument is NULL
• else { *op->resnull = true; }

[Aias00]

Hi @NotHimmel,

We re-verified this report by actually running it locally and by tracing the expression's reachability.

Verification:

• IS_UPDATEXML is an XmlExpr variant (primnodes.h), but neither gram.y nor ora_gram.y contains any production that creates it, and no updatexml SQL function exists in the catalog (SELECT ... FROM pg_proc WHERE proname ILIKE '%updatexml%' -> 0 rows). A SQL statement therefore cannot produce an IS_UPDATEXML expression node.
• The missing-hook fallback requires ora_updatexml_hook == NULL, but the hook is unconditionally assigned at extension load (ivorysql_ora.c:113), and Oracle mode requires the extension.

Decision: the executor branch exists but is unreachable from SQL - no syntax and no function can create the expression. The report does not reproduce. We will close PR #1673 and this issue.

[Aias00]

Closing per the verification above - the executor branch is unreachable from SQL.