How to convert empty yml element to empty properties key?

[igorjarm]

Is it possible to transform yml file to properties with empty arrays and complex objects?

Actual yml file in question is pretty complex, referencing elements defined in other parts of the same file.
Use case for this is to provide optional values or overrides to the element. The existence of the element is critical, but the contents are optional (see arrayOfSimpleReferences and complexEmptyReferences below).

Thank you in advance.

Description of the problem:

test.yml

a:
  simpleValue: 1
  arrayOfReferences: [ONE, TWO]
  complexReferences: {first: THREE, second: FOUR}
  simpleEmptyValue:
  arrayOfSimpleReferences: []
  complexEmptyReferences: {}

How I use yq:

yq eval-all -o=p test.yml
version 4.14.2

For simple values it actually works ok, see a.simpleEmptyValue below

a.simpleValue = 1
a.arrayOfReferences.0 = ONE
a.arrayOfReferences.1 = TWO
a.complexReferences.first = THREE
a.complexReferences.second = FOUR
a.simpleEmptyValue = 

I would expect the following. Is this possible to achieve, or is this a bug / feature request or even intended feature?

a.simpleValue = 1
a.arrayOfReferences.0 = ONE
a.arrayOfReferences.1 = TWO
a.complexReferences.first = THREE
a.complexReferences.second = FOUR
a.simpleEmptyValue = 
a.arrayOfSimpleReferences = 
a.complexEmptyReferences = 

[mikefarah]

Yep that can be done - I'm struggling to find a reference for what the conventions are for property files, do you have any references to back this up?

[igorjarm]

Thank you for a quick reply!

I'm also not aware of any convention dealing with this.
However I would still argue that even if not evident what exactly the contents are supposed to be, it's still more correct to provide at least evidence of the element's existence in the source yml file than nothing at all.

a.simpleEmptyValue = 
a.arrayOfSimpleReferences = 
a.complexEmptyReferences = 

To be fair, as an example test Java Spring configuration fails parsing such properties file.
Note: The source configuration in my case is yml, i use yq for analyzing hundreds of yml files.

@ConfigurationProperties(prefix = "a")
@Configuration
public class TestConfig {
    private String simpleEmptyValue;
    private List<String> arrayOfSimpleReferences;
    private Map<String,String> complexEmptyReferences;

with

Failed to bind properties under 'a.complex-empty-references' to java.util.Map<java.lang.String, java.lang.String>:
    Reason: No converter found capable of converting from type [java.lang.String] to type [java.util.Map<java.lang.String, java.lang.String>]

But it successfully parses the following properties

a.simpleEmptyValue = 0
a.arrayOfSimpleReferences.0 = one
a.complexEmptyReferences.value = other

[mikefarah]

I get what you are saying about seeing evidence of its existing, the fact the it doesn't work in Java is definitely an argument against it in my mind though.

That said, on thinking on this a little more, you can get what you want by running it through an expression like so to update empty arrays and maps:

yq e -o=props '(.. | select( (tag == "!!map" or tag =="!!seq") and length == 0)) = ""' file.yaml 

[igorjarm]

This is exactly what I need!
Thank you so much.