Function make_nulltest_from_distinct

src/backend/parser/parse_expr.c:3147–3162

* Produce a NullTest node from an IS [NOT] DISTINCT FROM NULL construct * * "arg" is the untransformed other argument */

 * "arg" is the untransformed other argument
 */
static Node *
make_nulltest_from_distinct(ParseState *pstate, A_Expr *distincta, Node *arg)
{
	NullTest   *nt = makeNode(NullTest);

	nt->arg = (Expr *) transformExprRecurse(pstate, arg);
	/* the argument can be any type, so don't coerce it */
	if (distincta->kind == AEXPR_NOT_DISTINCT)
		nt->nulltesttype = IS_NULL;
	else
		nt->nulltesttype = IS_NOT_NULL;
	/* argisrow = false is correct whether or not arg is composite */
	nt->argisrow = false;
	nt->location = distincta->location;
	return (Node *) nt;
}

/*
 * Produce a string identifying an expression by kind.