In transformRowExpr(), check for too many columns in the row.

A RowExpr with more than MaxTupleAttributeNumber columns would fail at
execution anyway, since we cannot form a tuple datum with more than that
many columns.  While heap_form_tuple() has a check for too many columns,
it emerges that there are some intermediate bits of code that don't
check and can be driven to failure with sufficiently many columns.
Checking this at parse time seems like the most appropriate place to
install a defense, since we already check SELECT list length there.

While at it, make the SELECT-list-length error use the same errcode
(TOO_MANY_COLUMNS) as heap_form_tuple does, rather than the generic
PROGRAM_LIMIT_EXCEEDED.

Per bug #17561 from Egor Chindyaskin.  The given test case crashes
in all supported branches (and probably a lot further back),
so patch all.

Discussion: https://postgr.es/m/17561-80350151b9ad2ad4@postgresql.org

src/backend/parser/parse_expr.c

@@ -2091,6 +2091,14 @@ transformRowExpr(ParseState *pstate, RowExpr *r, bool allowDefault)
 	newr->args = transformExpressionList(pstate, r->args,
 										 pstate->p_expr_kind, allowDefault);
 
+	/* Disallow more columns than will fit in a tuple */
+	if (list_length(newr->args) > MaxTupleAttributeNumber)
+		ereport(ERROR,
+				(errcode(ERRCODE_TOO_MANY_COLUMNS),
+				 errmsg("ROW expressions can have at most %d entries",
+						MaxTupleAttributeNumber),
+				 parser_errposition(pstate, r->location)));
+
 	/* Barring later casting, we consider the type RECORD */
 	newr->row_typeid = RECORDOID;
 	newr->row_format = COERCE_IMPLICIT_CAST;

src/backend/parser/parse_node.c

@@ -83,7 +83,7 @@ free_parsestate(ParseState *pstate)
 	 */
 	if (pstate->p_next_resno - 1 > MaxTupleAttributeNumber)
 		ereport(ERROR,
-				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				(errcode(ERRCODE_TOO_MANY_COLUMNS),
 				 errmsg("target lists can have at most %d entries",
 						MaxTupleAttributeNumber)));