Make get_stack_depth_rlimit() handle RLIM_INFINITY more sanely.

Rather than considering this result as meaning "unknown", report LONG_MAX.
This won't change what superusers can set max_stack_depth to, but it will
cause InitializeGUCOptions() to set the built-in default to 2MB not 100kB.
The latter seems like a fairly unreasonable interpretation of "infinity".
Per my investigation of odd buildfarm results as well as an old complaint
from Heikki.

Since this should persuade all the buildfarm animals to use a reasonable
stack depth setting during "make check", revert previous patch that dumbed
down a recursive regression test to only 5 levels.

src/backend/tcop/postgres.c

@@ -19,10 +19,11 @@
 
 #include "postgres.h"
 
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
 #include <time.h>
 #include <unistd.h>
-#include <signal.h>
-#include <fcntl.h>
 #include <sys/socket.h>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
@@ -4107,7 +4108,7 @@ PostgresMain(int argc, char *argv[], const char *username)
 /*
  * Obtain platform stack depth limit (in bytes)
  *
- * Return -1 if unlimited or not known
+ * Return -1 if unknown
  */
 long
 get_stack_depth_rlimit(void)
@@ -4123,7 +4124,10 @@ get_stack_depth_rlimit(void)
 		if (getrlimit(RLIMIT_STACK, &rlim) < 0)
 			val = -1;
 		else if (rlim.rlim_cur == RLIM_INFINITY)
-			val = -1;
+			val = LONG_MAX;
+		/* rlim_cur is probably of an unsigned type, so check for overflow */
+		else if (rlim.rlim_cur >= LONG_MAX)
+			val = LONG_MAX;
 		else
 			val = rlim.rlim_cur;
 	}

src/backend/utils/misc/guc.c

@@ -3485,14 +3485,14 @@ InitializeGUCOptions(void)
 	stack_rlimit = get_stack_depth_rlimit();
 	if (stack_rlimit > 0)
 	{
-		int			new_limit = (stack_rlimit - STACK_DEPTH_SLOP) / 1024L;
+		long		new_limit = (stack_rlimit - STACK_DEPTH_SLOP) / 1024L;
 
 		if (new_limit > 100)
 		{
 			char		limbuf[16];
 
 			new_limit = Min(new_limit, 2048);
-			sprintf(limbuf, "%d", new_limit);
+			sprintf(limbuf, "%ld", new_limit);
 			SetConfigOption("max_stack_depth", limbuf,
 							PGC_POSTMASTER, PGC_S_ENV_VAR);
 		}

src/test/regress/expected/plpgsql.out

@@ -4006,7 +4006,7 @@ $$ language plpgsql;
 -- "limit" is to prevent this from being inlined
 create function sql_recurse(float8) returns float8 as
 $$ select recurse($1) limit 1; $$ language sql;
-select recurse(5);
+select recurse(10);
  recurse 
 ---------
        0

src/test/regress/sql/plpgsql.sql

@@ -3211,7 +3211,7 @@ $$ language plpgsql;
 create function sql_recurse(float8) returns float8 as
 $$ select recurse($1) limit 1; $$ language sql;
 
-select recurse(5);
+select recurse(10);
 
 create function error1(text) returns text language sql as
 $$ SELECT relname::text FROM pg_class c WHERE c.oid = $1::regclass $$;