pam_limits: do not create file in check mode when it does not exist (#8057)

Do not create file in check mode when it does not exist.

changelogs/fragments/8057-pam_limits-check-mode.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "pam_limits - when the file does not exist, do not create it in check mode (https://github.com/ansible-collections/community.general/issues/8050, https://github.com/ansible-collections/community.general/pull/8057)."

plugins/modules/pam_limits.py

@@ -175,7 +175,6 @@ def main():
     limits_conf = '/etc/security/limits.conf'
 
     module = AnsibleModule(
-        # not checking because of daisy chain to file module
         argument_spec=dict(
             domain=dict(required=True, type='str'),
             limit_type=dict(required=True, type='str', choices=pam_types),
@@ -201,6 +200,7 @@ def main():
     new_comment = module.params['comment']
 
     changed = False
+    does_not_exist = False
 
     if os.path.isfile(limits_conf):
         if not os.access(limits_conf, os.W_OK):
@@ -208,7 +208,7 @@ def main():
     else:
         limits_conf_dir = os.path.dirname(limits_conf)
         if os.path.isdir(limits_conf_dir) and os.access(limits_conf_dir, os.W_OK):
-            open(limits_conf, 'a').close()
+            does_not_exist = True
             changed = True
         else:
             module.fail_json(msg="directory %s is not writable (check presence, access rights, use sudo)" % limits_conf_dir)
@@ -224,15 +224,20 @@ def main():
 
     space_pattern = re.compile(r'\s+')
 
+    if does_not_exist:
+        lines = []
+    else:
+        with open(limits_conf, 'rb') as f:
+            lines = list(f)
+
     message = ''
-    f = open(limits_conf, 'rb')
     # Tempfile
     nf = tempfile.NamedTemporaryFile(mode='w+')
 
     found = False
     new_value = value
 
-    for line in f:
+    for line in lines:
         line = to_native(line, errors='surrogate_or_strict')
         if line.startswith('#'):
             nf.write(line)
@@ -323,17 +328,17 @@ def main():
         message = new_limit
         nf.write(new_limit)
 
-    f.close()
     nf.flush()
 
-    with open(limits_conf, 'r') as content:
-        content_current = content.read()
-
     with open(nf.name, 'r') as content:
         content_new = content.read()
 
     if not module.check_mode:
-        # Copy tempfile to newfile
+        if does_not_exist:
+            with open(limits_conf, 'a'):
+                pass
+
+        # Move tempfile to newfile
         module.atomic_move(nf.name, limits_conf)
 
     try:
@@ -344,7 +349,7 @@ def main():
     res_args = dict(
         changed=changed,
         msg=message,
-        diff=dict(before=content_current, after=content_new),
+        diff=dict(before=b''.join(lines), after=content_new),
     )
 
     if backup: