Is there a directive to have the output generator inject Comments (for types that support them)?

[eli-xciv]

I'm looking for a way to specify a comment in a pkl file that will make it into a yaml file generated wtih pkl eval -f yaml my.pkl

example:
my.pkl

// Would Like to specify a comment here?
my: String = "My Pkl file"

Wanted output with -f yaml

# Would Like to specify a comment here?
my: My Pkl file

Is there currently a way to do this? Thanks in advance

[bioball]

There is not.

One existing pattern here is to change the output.text to include comments:

foo = "Hello there"

output {
  text = """
    # Some comment
    \(new YamlRenderer {}.renderDocument(module))
    """
}

Although, this doesn't work as well if you want to add a comment in the middle of a file.

[eli-xciv]

Hrrrrm, would it be worthwhile to put in a feature request to be able to add comments within a file (for those types that support it).

[holzensp]

There are still quite a few ways to do this. Take a look at the default definition of output here. You could easily imagine a comment: String field added there, and changing the definition of text to comment + "\n" + renderer.renderDocument(value).

However, that's not a general solution, because formats like JSON don't have comments (and so you'd only introduce leading \n). Since it can't be format agnostic, you'd be setting the renderer to the expected format anyway, so then you might as well set output.text the way @bioball did above.

One thing that could be generally applicable is to add a prefix: String = "" and suffix: String = "", such that text = prefix + renderer.renderDocument(value) + suffix. If anything, my point is that it'll take a little more refinement to turn this into a proper feature request; maybe continue this Discussion.

[eli-xciv]

@holzensp Thanks! I'll have to checkout using fields and play around with the output renderer(s).

At the start I was thinking of a more abstract implementation akin to a Java Annotation that would cause the renderer to inject a comment (if the backing file structure supports comments)

[holzensp]

If you want, you can. If you define class MyAnnotation extends Annotation { ... }, you can put a @MyAnnotation over object members. pkl:reflect will see those annotations. It does seem a somewhat roundabout way to achieve something that sounds like it should be simpler (could this be an instance of the XY problem?).