Jira (PUP-11505) Unexpected results using stdlib's to_yaml with data containing repeated variables

[Alexander Fisher (Jira)]

Alexander Fisher created an issue

Puppet / PUP-11505 Unexpected results using stdlib's to_yaml with data containing repeated variables Issue Type: Bug Assignee: Unassigned Created: 2022/04/12 9:23 AM Priority: Normal Reporter: Alexander Fisher Puppet Version: 6/7 ** I wasn't sure where to file this, but I encountered some unexpected behaviour today. Given the following puppet code $array = [ 'one', 'two', 'three']   notice( { 'foo' => $array, 'bar' => $array, 'foobar' => $array, }.to_yaml )   # These `flatten`s look superfluous, but aren't   notice( { 'foo' => $array.flatten, 'bar' => $array.flatten, 'foobar' => $array.flatten, }.to_yaml ) I'd expect to notice the same YAML being output.  Instead, in the version where I don't, (seemingly randomly call `flatten`), I get yaml with anchors (which I happen not to like). ie  ❯ puppet apply -t test.pp Info: Loading facts Notice: Scope(Class[main]): --- foo: &1 - one - two - three bar: *1 foobar: *1   Notice: Scope(Class[main]): --- foo: - one - two - three bar: - one - two - three foobar: - one - two - three Whilst I understand that there's an issue with values being passed to the to_yaml function by reference and `flatten` gets around this by creating 3 new objects, I don't feel this meets the https://en.wikipedia.org/wiki/Principle_of_least_astonishment test. I don't think it's documented anywhere that puppet variables can act this way with functions. Add Comment

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[Alexander Fisher (Jira)]

Alexander Fisher updated an issue

Puppet / PUP-11505 Unexpected results using stdlib's to_yaml with data containing repeated variables

Change By: Alexander Fisher *Puppet Version: 6/7* **

I wasn't sure where to file this, but I encountered some unexpected behaviour today. Given the following puppet code

{code:puppet}$array = [  'one',  'two',  'three']

notice(   {     'foo'      => $array,     'bar'      => $array,     'foobar' => $array,   }.to_yaml ) # These `flatten`s look superfluous, but aren't notice(   {     'foo'      => $array.flatten,     'bar'      => $array.flatten,     'foobar' => $array.flatten,   }.to_yaml

) {code}

I'd expect to notice the same YAML being output.  Instead, in the version where I don't, (seemingly randomly call `flatten`), I get yaml with anchors (which I happen not to like). ie

{noformat}❯ puppet apply -t test.pp

Info: Loading facts Notice: Scope(Class[main]): --- foo: &1 - one - two - three bar: *1 foobar: *1 Notice: Scope(Class[main]): --- foo: - one - two - three bar: - one - two - three foobar: - one - two - three

{noformat}

Whilst I understand that there's an issue with values being passed to the to_yaml function by reference and `flatten` gets around this by creating 3 new objects, I don't feel this meets the [https://en.wikipedia.org/wiki/Principle_of_least_astonishment] test.

I don't think it's documented anywhere that _puppet_ variables can act this way with functions.

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[Alexander Fisher (Jira)]

Alexander Fisher updated an issue

Puppet / PUP-11505 Unexpected results using stdlib's to_yaml with data containing repeated variables Change By: Alexander Fisher

*Puppet Version: 6/7*

[Josh Cooper (Jira)]

Josh Cooper commented on PUP-11505

Re: Unexpected results using stdlib's to_yaml with data containing repeated variables Technically, puppet is behaving correctly. The same array object is referenced in multiple times and to_yaml produced valid YAML, preserving the fact that the same array object was emitted 3 times. Some yaml bindings allow the behavior to be altered, such PyYAML's ignore_aliases https://github.com/yaml/pyyaml/blob/8cdff2c80573b8be8e8ad28929264a913a63aa33/lib/yaml/representer.py#L131 This post goes into more detail: https://ttl255.com/yaml-anchors-and-aliases-and-how-to-disable-them/ The other option is to deep clone the object, which flatten is effectively doing, but only the caller really knows if the object can be deep cloned.

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