Why use a Collection instead of just a slice?

That was the whole point of the change. Collections handle trailing comments and have uniform formatting

Okay, fair. We can leave this for now, and presumably in the future this won't be a problem since Apply is going away.

This seems like it's formatted incorrectly to me. Either we should move the comments above the 1 line, or keep it after the closing parens.

I have to guess that this is consistent with what we do for all collections (lists, tuples, records)...

If that's the case, we can make a GitHub issue and try to fix that at some point

I'm okay with ignoring for now if we do something like that in order to avoid leaving this in

#7486

Looking back at this, I don't see how that is not the right formatting, here's the original:

1(i,p#
):f
n

and it is being formatted as:

1(
    i,
    p, #
) : f
n

To me, the comment is obviously meant for the last arg p and since the comment there forces this to be multi-line, that causes the args to be outdented. This feels like the correct formatting to me.

Seems like another case that a comment sneaks inside of parens incorrectly.

The original is:

1(ts((0
)
#
)
)f:i7f
e

which if I formatted this in my brain (which is hard because this is nonsense):

1(
    ts(
        0,
        #
    ),
)
    f : i7f
e

which is pretty close to what it does:

1(
    ts(
        0,

        #
    ),
)
    f : i7f
e

With migration it should be:

1(
    ts(
        0,

        #
    ),
)(f) : i7f
e

Why?

1. 1(...) f is a PNC apply as the func in a WS apply. With migration we would turn the outer WS apply in a PNC apply.
2. The 0 inside of ts(...) has a newline inside the ParensAround, and then another newline in SpacesAfter before the comment. That's the reason for the blank in between after we drop the unneeded ParensAround.

And that's really it.

I think this mostly closely respects the vertical whitespace requested by the user (without being excessive), while indenting and separating terms correctly - as well as making it easy to add a new arg to both 1(..) and ts(..) by adding the trailing commas when outdented.