Anchors formatted with unexpected merge tags

[badouralix]

Considering the following yaml file :

a: &a
b:
  <<: *a

Formatting with yamlfmt returns this :

a: &a
b:
  !!merge <<: *a

The expectation here is to preserve the original file and not to add the extra !!merge tag
This results in the following error in vscode : Unresolved tag: tag:yaml.org,2002:mergeYAML

I haven't found any reference of this tag in yamlfmt, good chance it comes directly from gopkg.in/yaml.v3
About !!merge, it shows up in this reference : https://yaml.org/type/merge.html

Edit : it seems it does come from gopkg.in/yaml.v3 indeed : https://go.dev/play/p/DSNN-bUHCIh

[braydonk]

Thanks for bringing this to my attention! I don't really know much about this particular yaml feature.

This tag is being written by the library. This is the comment in the library that explains why this tag is included:
https://github.com/braydonk/yaml/blob/v3/encode.go#L439-L440

I think it kind of makes sense; << on its own could technically be ambiguously a literal string or a merge operator. But I think it's a pretty silly reason to always include it in the representation for that reason, because I can't imagine a scenario where someone would use << and wouldn't mean !!merge.

I'll try and add an option for this in the yaml library, not sure what I'll call it yet but probably along the lines of assume_merge_operator that will deliberately drop the merge tag from the representation. I can get it in the next release that I'm planning for this weekend.

[braydonk]

Merged this, release should be happening on the weekend.