Update value with saving comment

[igor-lemon]

Hi.
Is it possible to save comments after value changing?

args:
        #somecomment
        objectKey: objectVal #here some comment

After call doc.setIn(['args', 'objectKey'], 'objectValNew') I have

args:
        #somecomment
        objectKey: objectValNew

but I would be want to have

args:
        #somecomment
        objectKey: objectValNew #here some comment

[eemeli]

That would indeed make sense. The semantics of set and setIn currently consider the comment and anchor to have been a part of the original value, which gets replaced. But that can clearly break stuff:

const doc = YAML.parseDocument(`
  a: &A value
  b: *A
`)
doc.set('a', 'foo')
String(doc)
// Error: Alias node must be after source node

Fixing this might be a breaking change, so it's good that I'm working on yaml@2 just now. At least the anchor should almost certainly stay no matter what; probably the comment as well?

[eemeli]

I managed to solve this for scalar values, which is probably most of the real-world usage. To also make this work for collections, the semantics of set() and some of the other accessors would need to change, such that they always apply a wrapper to the value. That in turn would mean that get()ting a value that you've set() isn't always the same.

Also, routing the internal dependencies such that wrapping input would be possible within accessors would get a little hairy, so I'm going to leave this only mostly fixed, and see if anyone complains.

[igor-lemon]

Wow! Thanks!