Merge pull request #17248 from abadger/facts-module-dev-docs

Couple things to watch out for when reviewing facts modules

docsite/rst/developing_modules.rst

@@ -721,7 +721,14 @@ The following  checklist items are important guidelines for people who want to c
   fields of a dictionary and return the dictionary.
 * When fetching URLs, please use either fetch_url or open_url from ansible.module_utils.urls 
   rather than urllib2; urllib2 does not natively verify TLS certificates and so is insecure for https. 
-
+* facts modules must return facts in the ansible_facts field of the result
+  dictionary. :ref:`module_provided_facts`
+* modules that are purely about fact gathering need to implement check_mode.
+  they should not cause any changes anyway so it should be as simple as adding
+  check_mode=True when instantiating AnsibleModule.  (The reason is that
+  playbooks which conditionalize based on fact information will only
+  conditionalize correctly in check_mode if the facts are returned in
+  check_mode).
 
 Windows modules checklist
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