Incorrect indentation with lists

When using indentation this seems to be applied to the value of the list instead of to the list itself, as you can see below indent=4 is applied after the leading - and not to the list itself.

>>> print(yaml.dump(data['vars']['yaml'], indent=4, allow_unicode=True, default_flow_style=False))
list_of_dict_attr:
-   attr1: value1
    attr2: value2
    attr3:
    - item1
    - item2
single_attr: value1
>>> print(yaml.dump(data['vars']['yaml'], indent=2, allow_unicode=True, default_flow_style=False))
list_of_dict_attr:
- attr1: value1
  attr2: value2
  attr3:
  - item1
  - item2
single_attr: value1

original issue https://github.com/ansible/ansible/issues/48865

[pbasista]

From my point of view, the most widely-accepted indentation style for sequences is the one used multiple times in the official YAML specification. For instance, in section 2.1, example 2.3 looks like this:

american:
  - Boston Red Sox
  - Detroit Tigers
  - New York Yankees
national:
  - New York Mets
  - Chicago Cubs
  - Atlanta Braves

The question is whether tools like pyyaml should render sequences in such a way for indentation of size 4 or for indentation of size 2.

I would argue that it seems incorrect to render sequences in such a way for indentation of size 4, because other items would visually appear to be indented more:

mapping:
    one: 1
    two: 2
list:
  - 1
  - 2

Therefore, I think that it is more appropriate to render sequences in such a way for indentation of size 2:

mapping:
  one: 1
  two: 2
list:
  - 1
  - 2

That being said, someone may prefer to not indent sequence items to a level that is visually similar to the indentation level of the other items. That is a fair requirement, but in order to fully support it, there would have to be a separate configuration option for indentation size of sequences.

[andreif]

The workaround mentioned above:

class Dumper(yaml.Dumper):
    def increase_indent(self, flow=False, *args, **kwargs):
        return super().increase_indent(flow=flow, indentless=False)

print(yaml.dump(data, Dumper=Dumper))

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