pgbench: Improve error-handling in \sleep command.

This commit improves pgbench \sleep command so that it handles
the following three cases more properly.

(1) When only one argument was specified in \sleep command and
    it's not a number, previously pgbench reported a confusing error
    message like "unrecognized time unit, must be us, ms or s".
    This commit fixes this so that more proper error message like
    "invalid sleep time, must be an integer" is reported.

(2) When two arguments were specified in \sleep command and
    the first argument was not a number, previously pgbench treated
    that argument as the sleep time 0. No error was reported in this
    case. This commit fixes this so that an error is thrown in this
    case.

(3) When a variable was specified as the first argument in \sleep
    command and the variable stored non-digit value, previously
    pgbench treated that argument as the sleep time 0. No error
    was reported in this case. This commit fixes this so that
    an error is thrown in this case.

Author: Kota Miyake
Reviewed-by: Hayato Kuroda, Alvaro Herrera, Fujii Masao
Discussion: https://postgr.es/m/23b254daf20cec4332a2d9168505dbc9@oss.nttdata.com

src/bin/pgbench/pgbench.c

@@ -2953,7 +2953,16 @@ evaluateSleep(CState *st, int argc, char **argv, int *usecs)
 			pg_log_error("%s: undefined variable \"%s\"", argv[0], argv[1] + 1);
 			return false;
 		}
+
 		usec = atoi(var);
+
+		/* Raise an error if the value of a variable is not a number */
+		if (usec == 0 && !isdigit((unsigned char) *var))
+		{
+			pg_log_error("%s: invalid sleep time \"%s\" for variable \"%s\"",
+						 argv[0], var, argv[1] + 1);
+			return false;
+		}
 	}
 	else
 		usec = atoi(argv[1]);
@@ -4788,18 +4797,42 @@ process_backslash_command(PsqlScanState sstate, const char *source)
 		 * will be parsed with atoi, which ignores trailing non-digit
 		 * characters.
 		 */
-		if (my_command->argc == 2 && my_command->argv[1][0] != ':')
+		if (my_command->argv[1][0] != ':')
 		{
 			char	   *c = my_command->argv[1];
+			bool		have_digit = false;
 
-			while (isdigit((unsigned char) *c))
+			/* Skip sign */
+			if (*c == '+' || *c == '-')
 				c++;
+
+			/* Require at least one digit */
+			if (*c && isdigit((unsigned char) *c))
+				have_digit = true;
+
+			/* Eat all digits */
+			while (*c && isdigit((unsigned char) *c))
+				c++;
+
 			if (*c)
+			{
+				if (my_command->argc == 2 && have_digit)
 				{
 					my_command->argv[2] = c;
 					offsets[2] = offsets[1] + (c - my_command->argv[1]);
 					my_command->argc = 3;
 				}
+				else
+				{
+					/*
+					 * Raise an error if argument starts with non-digit
+					 * character (after sign).
+					 */
+					syntax_error(source, lineno, my_command->first_line, my_command->argv[0],
+								 "invalid sleep time, must be an integer",
+								 my_command->argv[1], offsets[1] - start_offset);
+				}
+			}
 		}
 
 		if (my_command->argc == 3)