[ansible-project] Cannot get customized facts when pushing with "--check"

Hi gentlemen,
We are using the Ansible to manage many servers, and we like the dry run
mode which with parameters "--check" and "--diff". We always run with these
parameters first to verify that if the changes will be made correctly.
The customized facts are very helpful, to generate some dynamic facts. But
the trouble is, when we ran with "--check", ansible skipped the customized
module.
So we can't use the dry run to check before we push if there are some
customized facts used in templates files.
Is there a way to fix this or work around?

Here are the detailed informations:

[[email protected] ansible]# cat roles/myfacts/tasks/main.yml
---
- name: run myfacts module to get customized facts
   myfacts: get_facts=yes

- name: update file with the customized facts
   template: src=myfacts.txt.j2 dest=/tmp/myfacts.txt

[[email protected] ansible]# cat roles/myfacts/templates/myfacts.txt.j2
ansible_private_ipv4_address : {{ ansible_private_ipv4_address }}

[[email protected] ansible]# cat library/heylinux/myfacts

#!/usr/bin/python

import sys
import json
import shlex
import commands
import re

def get_ansible_private_ipv4_address():
     iprex = "(^192\.168)|(^10\.)|(^172\.1[6-9])|(^172\.2[0-9])|(^172\.3[0-1])"
     output = commands.getoutput("""/sbin/ifconfig |grep "Link encap" |awk '{print $1}' |grep -wv 'lo'""")
     nics = output.split('\n')
     for i in nics:
         ipaddr = commands.getoutput("""/sbin/ifconfig %s |grep -w "inet addr" |cut -d: -f2 | awk '{print $1}'""" % (i))
         if re.match(iprex,ipaddr):
             ansible_private_ipv4_address = ipaddr
             return ansible_private_ipv4_address

ansible_facts_dict = {
         "changed" : False,
         "ansible_facts" : {
             }
     }

args_file = sys.argv[1]
args_data = file(args_file).read()

arguments = shlex.split(args_data)
for arg in arguments:
     if "=" in arg:
         (key, value) = arg.split("=")
         if key == "get_facts" and value == "yes":
             ansible_private_ipv4_address = get_ansible_private_ipv4_address()
             ansible_facts_dict['ansible_facts']['ansible_private_ipv4_address'] = ansible_private_ipv4_address

print json.dumps(ansible_facts_dict)


[[email protected] ansible]# cat myfacts.yml
---
- hosts: all
   roles:
   - myfacts

[root@idc1-server1 ansible]#ansroot myfacts.yml -i hosts.idc1 --limit
idc1-server1
PLAY [all]
********************************************************************

GATHERING FACTS
***************************************************************
ok: [idc1-server1]

TASK: [myfacts | run myfacts module to get customized facts] **************
ok: [idc1-server1]

TASK: [myfacts | update file with the customized facts]
*********************
changed: [idc1-server1]

PLAY RECAP
********************************************************************
idc1-server1 : ok=3 changed=1 unreachable=0
failed=0

[root@idc1-server1 ansible]#ansroot myfacts.yml -i hosts.idc1 --limit
idc1-server1 --check --diff
PLAY [all]
********************************************************************

GATHERING FACTS
***************************************************************

ok: [idc1-server1]

TASK: [myfacts | run myfacts module to get customized facts] **************
skipping: [idc1-server1]

TASK: [myfacts | update file with the customized facts]
*********************
fatal: [idc1-server1] => {'msg': "One or more undefined variables:
'ansible_private_ipv4_address' is undefined", 'failed': True}
fatal: [idc1-server1] => {'msg': "One or more undefined variables:
'ansible_private_ipv4_address' is undefined", 'failed': True}

FATAL: all hosts have already failed -- aborting

PLAY RECAP
********************************************************************
            to retry, use: --limit @/root/myfacts.retry

idc1-server1 : ok=1 changed=0 unreachable=1
failed=0