Updating yarn.list to not fail when when warnings are emitted (#6129)

* Updating yarn.list to not fail when when warnings are emitted

* Adding changelog fragment

* Adding _process_yarn_error function

* - Adding back changes to the changelog fragment
- Fixing formatting

* Fix trailing whitespace

* Update plugins/modules/yarn.py

Co-authored-by: Felix Fontein <felix@fontein.de>

---------

Co-authored-by: Felix Fontein <felix@fontein.de>

changelogs/fragments/6127-yarn-ignore-warnings.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - yarn - fixes bug where yarn module tasks would fail when warnings were emitted from Yarn. The ``yarn.list`` method was not filtering out warnings (https://github.com/ansible-collections/community.general/issues/6127).

plugins/modules/yarn.py

@@ -226,6 +226,15 @@ class Yarn(object):
 
         return None, None
 
+    def _process_yarn_error(self, err):
+        try:
+            # We need to filter for errors, since Yarn warnings are included in stderr
+            for line in err.splitlines():
+                if json.loads(line)['type'] == 'error':
+                    self.module.fail_json(msg=err)
+        except Exception:
+            self.module.fail_json(msg="Unexpected stderr output from Yarn: %s" % err, stderr=err)
+
     def list(self):
         cmd = ['list', '--depth=0', '--json']
 
@@ -240,8 +249,7 @@ class Yarn(object):
         # because it only only lists binaries, but `yarn global add` can install libraries too.
         result, error = self._exec(cmd, run_in_check_mode=True, check_rc=False, unsupported_with_global=True)
 
-        if error:
-            self.module.fail_json(msg=error)
+        self._process_yarn_error(error)
 
         for json_line in result.strip().split('\n'):
             data = json.loads(json_line)
@@ -279,9 +287,7 @@ class Yarn(object):
         cmd_result, err = self._exec(['outdated', '--json'], True, False, unsupported_with_global=True)
 
         # the package.json in the global dir is missing a license field, so warnings are expected on stderr
-        for line in err.splitlines():
-            if json.loads(line)['type'] == 'error':
-                self.module.fail_json(msg=err)
+        self._process_yarn_error(err)
 
         if not cmd_result:
             return outdated