Function ParseComplexProjection

src/backend/parser/parse_func.c:1966–2033

* ParseComplexProjection - * handles function calls with a single argument that is of complex type. * If the function call is actually a column projection, return a suitably * transformed expression tree. If not, return NULL. */

 *	  transformed expression tree.  If not, return NULL.
 */
static Node *
ParseComplexProjection(ParseState *pstate, const char *funcname, Node *first_arg,
					   int location)
{
	TupleDesc	tupdesc;
	int			i;

	/*
	 * Special case for whole-row Vars so that we can resolve (foo.*).bar even
	 * when foo is a reference to a subselect, join, or RECORD function. A
	 * bonus is that we avoid generating an unnecessary FieldSelect; our
	 * result can omit the whole-row Var and just be a Var for the selected
	 * field.
	 *
	 * This case could be handled by expandRecordVariable, but it's more
	 * efficient to do it this way when possible.
	 */
	if (IsA(first_arg, Var) &&
		((Var *) first_arg)->varattno == InvalidAttrNumber)
	{
		ParseNamespaceItem *nsitem;

		nsitem = GetNSItemByRangeTablePosn(pstate,
										   ((Var *) first_arg)->varno,
										   ((Var *) first_arg)->varlevelsup);
		/* Return a Var if funcname matches a column, else NULL */
		return scanNSItemForColumn(pstate, nsitem,
								   ((Var *) first_arg)->varlevelsup,
								   funcname, location);
	}

	/*
	 * Else do it the hard way with get_expr_result_tupdesc().
	 *
	 * If it's a Var of type RECORD, we have to work even harder: we have to
	 * find what the Var refers to, and pass that to get_expr_result_tupdesc.
	 * That task is handled by expandRecordVariable().
	 */
	if (IsA(first_arg, Var) &&
		((Var *) first_arg)->vartype == RECORDOID)
		tupdesc = expandRecordVariable(pstate, (Var *) first_arg, 0);
	else
		tupdesc = get_expr_result_tupdesc(first_arg, true);
	if (!tupdesc)
		return NULL;			/* unresolvable RECORD type */

	for (i = 0; i < tupdesc->natts; i++)
	{
		Form_pg_attribute att = TupleDescAttr(tupdesc, i);

		if (strcmp(funcname, NameStr(att->attname)) == 0 &&
			!att->attisdropped)
		{
			/* Success, so generate a FieldSelect expression */
			FieldSelect *fselect = makeNode(FieldSelect);

			fselect->arg = (Expr *) first_arg;
			fselect->fieldnum = i + 1;