Make 'required' optional in module docs (#15906)

Updated module dev docs, doc build, ansible-doc to match

docsite/rst/developing_modules.rst

@@ -638,8 +638,8 @@ The following  checklist items are important guidelines for people who want to c
     * Module documentation should briefly and accurately define what each module and option does, and how it works with others in the underlying system. Documentation should be written for broad audience--readable both by experts and non-experts. This documentation is not meant to teach a total novice, but it also should not be reserved for the Illuminati (hard balance).
     * If an argument takes both C(True)/C(False) and C(Yes)/C(No), the documentation should use C(True) and C(False). 
     * Descriptions should always start with a Capital letter and end with a full stop. Consistency always helps.
-    * The `required` setting should always be present, be it true *or* false
-    * If `required` is false, you should document `default`, even if the default is 'null' (which is the default if no parameter is supplied). Make sure default parameter in docs matches default parameter in code.
+    * The `required` setting is only required when true, otherwise it is assumed to be false.
+    * If `required` is false/missing, `default` may be specified (assumed 'null' if missing). Ensure that the default parameter in docs matches default parameter in code.
     * Documenting `default` is not needed for `required: true`.
     * Remove unnecessary doc like `aliases: []` or `choices: []`.
     * The version is not a float number and value the current development version.

hacking/module_formatter.py

@@ -289,8 +289,10 @@ def process_module(module, options, env, template, outputname, module_map, alias
                 del doc['options'][k]['version_added']
             if not 'description' in doc['options'][k]:
                 raise AnsibleError("Missing required description for option %s in %s " % (k, module))
-            if not 'required' in doc['options'][k]:
-                raise AnsibleError("Missing required 'required' for option %s in %s " % (k, module))
+
+            required_value = doc['options'][k].get('required', False)
+            if not isinstance(required_value, bool):
+                raise AnsibleError("Invalid required value '%s' for option '%s' in '%s' (must be truthy)" % (required_value, k, module))
             if not isinstance(doc['options'][k]['description'],list):
                 doc['options'][k]['description'] = [doc['options'][k]['description']]
 

lib/ansible/cli/doc.py

@@ -219,9 +219,7 @@ class DocCLI(CLI):
             opt = doc['options'][o]
             desc = CLI.tty_ify(" ".join(opt['description']))
 
-            required = opt.get('required')
-            if required is None:
-                raise("Missing required field 'Required'")
+            required = opt.get('required', False)
             if not isinstance(required, bool):
                 raise("Incorrect value for 'Required', a boolean is needed.: %s" % required)
             if required:
@@ -275,8 +273,8 @@ class DocCLI(CLI):
             if 'choices' in opt:
                 choices = ", ".join(str(i) for i in opt['choices'])
                 desc = desc + " (Choices: " + choices + ")"
-            if 'default' in opt:
-                default = str(opt['default'])
+            if 'default' in opt or not required:
+                default = str(opt.get('default', '(null)'))
                 desc = desc + " [Default: " + default + "]"
             text.append("%s\n" % textwrap.fill(CLI.tty_ify(desc), limit, initial_indent=opt_indent, subsequent_indent=opt_indent))