fix issue with legacy pugins and no docs (#78686)

* fix issue with legacy pugins and no docs

changelogs/fragments/legacy_no_file_skip.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - ansible-doc will not traceback when legacy plugins don't have docs nor adjacent file with docs

lib/ansible/utils/plugin_docs.py

@@ -340,6 +340,7 @@ def get_plugin_docs(plugin, plugin_type, loader, fragment_loader, verbose):
     if not docs[0]:
         try:
             newfile = _find_adjacent(filename, plugin, C.DOC_EXTENSIONS)
+            if newfile:
                 docs = get_docstring(newfile, fragment_loader, verbose=verbose, collection_name=collection_name, plugin_type=plugin_type)
         except Exception as e:
             raise AnsibleParserError('Adjacent file %s did not contain a DOCUMENTATION attribute (%s)' % (plugin, filename), orig_exc=e)

test/integration/targets/ansible-doc/filter_plugins/other.py

@@ -19,4 +19,5 @@ class FilterModule(object):
     def filters(self):
         return {
             'donothing': donothing,
+            'nodocs': donothing,
         }

test/integration/targets/ansible-doc/runme.sh

@@ -160,6 +160,9 @@ count=$(ANSIBLE_LIBRARY='./nolibrary' ansible-doc -l ansible.builtin |wc -l)
 [ "$(ansible-doc -t filter --playbook-dir ./ donothing| wc -l)" -gt "0" ]
 [ "$(ansible-doc -t filter --playbook-dir ./ ansible.legacy.donothing| wc -l)" -gt "0" ]
 
+# no docs and no sidecar
+ansible-doc -t filter --playbook-dir ./ nodocs 2>&1| grep -c 'missing documentation' || true
+
 # produce 'sidecar' docs for module
 [ "$(ansible-doc -M ./library test_win_module| wc -l)" -gt "0" ]
 [ "$(ansible-doc --playbook-dir ./ test_win_module| wc -l)" -gt "0" ]