Limit max parameter number with MaxAllocSize

MaxAllocSize puts an upper bound on the largest possible parameter
number ($268435455).  Use that limit instead of INT_MAX to report that
no parameters exist beyond that point instead of reporting an error
about the maximum allocation size being exceeded.

Author: Erik Wienhold <ewie@ewie.name>
Discussion: https://www.postgresql.org/message-id/flat/5d216d1c-91f6-4cbe-95e2-b4cbd930520c@ewie.name

src/backend/parser/parse_param.c

@@ -31,6 +31,7 @@
 #include "parser/parse_param.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
+#include "utils/memutils.h"
 
 
 typedef struct FixedParamState
@@ -136,7 +137,7 @@ variable_paramref_hook(ParseState *pstate, ParamRef *pref)
 	Param	   *param;
 
 	/* Check parameter number is in range */
-	if (paramno <= 0 || paramno > INT_MAX / sizeof(Oid))
+	if (paramno <= 0 || paramno > MaxAllocSize / sizeof(Oid))
 		ereport(ERROR,
 				(errcode(ERRCODE_UNDEFINED_PARAMETER),
 				 errmsg("there is no parameter $%d", paramno),

src/test/regress/expected/prepare.out

@@ -184,6 +184,11 @@ SELECT name, statement, parameter_types, result_types FROM pg_prepared_statement
       |     UPDATE tenk1 SET stringu1 = $2 WHERE unique1 = $1;           |                                                    | 
 (6 rows)
 
+-- max parameter number and one above
+PREPARE q9 AS SELECT $268435455, $268435456;
+ERROR:  there is no parameter $268435456
+LINE 1: PREPARE q9 AS SELECT $268435455, $268435456;
+                                         ^
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements

src/test/regress/sql/prepare.sql

@@ -78,6 +78,9 @@ PREPARE q8 AS
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements
     ORDER BY name;
 
+-- max parameter number and one above
+PREPARE q9 AS SELECT $268435455, $268435456;
+
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements