yaml callback: prevent plugin from modifying PyYAML (#3478) (#3494)

* Prevent yaml callback from modifying PyYAML.

* Fix changelog fragment.

* Update changelogs/fragments/3478-yaml-callback.yml

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>

Co-authored-by: Brian Scholer <1260690+briantist@users.noreply.github.com>
(cherry picked from commit 5895e50185)

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

changelogs/fragments/3478-yaml-callback.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "yaml callback plugin - avoid modifying PyYAML so that other plugins using it on the controller, like the ``to_yaml`` filter, do not produce different output (https://github.com/ansible-collections/community.general/issues/3471, https://github.com/ansible-collections/community.general/pull/3478)."

plugins/callback/yaml.py

@@ -42,28 +42,29 @@ def should_use_block(value):
     return False
 
 
-def my_represent_scalar(self, tag, value, style=None):
+class MyDumper(AnsibleDumper):
-    """Uses block style for multi-line strings"""
+    def represent_scalar(self, tag, value, style=None):
-    if style is None:
+        """Uses block style for multi-line strings"""
-        if should_use_block(value):
+        if style is None:
-            style = '|'
+            if should_use_block(value):
-            # we care more about readable than accuracy, so...
+                style = '|'
-            # ...no trailing space
+                # we care more about readable than accuracy, so...
-            value = value.rstrip()
+                # ...no trailing space
-            # ...and non-printable characters
+                value = value.rstrip()
-            value = ''.join(x for x in value if x in string.printable or ord(x) >= 0xA0)
+                # ...and non-printable characters
-            # ...tabs prevent blocks from expanding
+                value = ''.join(x for x in value if x in string.printable or ord(x) >= 0xA0)
-            value = value.expandtabs()
+                # ...tabs prevent blocks from expanding
-            # ...and odd bits of whitespace
+                value = value.expandtabs()
-            value = re.sub(r'[\x0b\x0c\r]', '', value)
+                # ...and odd bits of whitespace
-            # ...as does trailing space
+                value = re.sub(r'[\x0b\x0c\r]', '', value)
-            value = re.sub(r' +\n', '\n', value)
+                # ...as does trailing space
-        else:
+                value = re.sub(r' +\n', '\n', value)
-            style = self.default_style
+            else:
-    node = yaml.representer.ScalarNode(tag, value, style=style)
+                style = self.default_style
-    if self.alias_key is not None:
+        node = yaml.representer.ScalarNode(tag, value, style=style)
-        self.represented_objects[self.alias_key] = node
+        if self.alias_key is not None:
-    return node
+            self.represented_objects[self.alias_key] = node
+        return node
 
 
 class CallbackModule(Default):
@@ -79,7 +80,6 @@ class CallbackModule(Default):
 
     def __init__(self):
         super(CallbackModule, self).__init__()
-        yaml.representer.BaseRepresenter.represent_scalar = my_represent_scalar
 
     def _dump_results(self, result, indent=None, sort_keys=True, keep_invocation=False):
         if result.get('_ansible_no_log', False):
@@ -121,7 +121,7 @@ class CallbackModule(Default):
 
         if abridged_result:
             dumped += '\n'
-            dumped += to_text(yaml.dump(abridged_result, allow_unicode=True, width=1000, Dumper=AnsibleDumper, default_flow_style=False))
+            dumped += to_text(yaml.dump(abridged_result, allow_unicode=True, width=1000, Dumper=MyDumper, default_flow_style=False))
 
         # indent by a couple of spaces
         dumped = '\n  '.join(dumped.split('\n')).rstrip()

tests/integration/targets/callback_yaml/tasks/main.yml

@@ -58,3 +58,40 @@
           "PLAY RECAP *********************************************************************",
           "testhost                   : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   "
         ]
+      - name: Test to_yaml
+        environment:
+          ANSIBLE_NOCOLOR: 'true'
+          ANSIBLE_FORCE_COLOR: 'false'
+          ANSIBLE_STDOUT_CALLBACK: community.general.yaml
+        playbook: |
+          - hosts: testhost
+            gather_facts: false
+            vars:
+              data: |
+                line 1
+                line 2
+                line 3
+            tasks:
+              - name: Test to_yaml
+                debug:
+                  msg: "{{ '{{' }}'{{ '{{' }}'{{ '}}' }} data | to_yaml {{ '{{' }}'{{ '}}' }}'{{ '}}' }}"
+        # The above should be:   msg: "{{ data | to_yaml }}"
+        # Unfortunately, the way Ansible handles templating, we need to do some funny 'escaping' tricks...
+        expected_output: [
+          "",
+          "PLAY [testhost] ****************************************************************",
+          "",
+          "TASK [Test to_yaml] ************************************************************",
+          "ok: [testhost] => ",
+          "  msg: |-",
+          "    'line 1",
+          "  ",
+          "      line 2",
+          "  ",
+          "      line 3",
+          "  ",
+          "      '",
+          "",
+          "PLAY RECAP *********************************************************************",
+          "testhost                   : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   "
+        ]