Do something like a "double hardline" / two line breaks

[tfachmann]

Take for example some toml code:

[dev-dependencies]
criterion = "0.4"
[ bench ]
name = "benchmark"
harness = false

Assume that the block [dev-dependencies] ... is named a (table).

Is it possible to force exactly two line breaks after tables?

i.e.

[dev-dependencies]
criterion = "0.4"

[ bench ]
name = "benchmark"
harness = false

I know that it's possible to (table) @allow_blank_line_before such that an additional line break is allowed if the user provides it, however I want to make sure that it will format it to always be one more line break.

[Xophmeister]

Thanks for your suggestion 👍 Inserting empty lines, when they're not in the input, is certainly frustrating. Indeed, some languages are formatted with double empty lines between certain contexts. So there's definitely a case for this (and it's come up before).

I don't think this would ever be relevant in a softline context, so the options I can see:

1. The @{append,prepend}_hardline captures could take an optional parameter, in the form of a predicate, that indicates the number of newlines to add (defaulting to 1). For example:

   (
     [
       (some)
       (things)
     ] @append_hardline
     .
     (_)
   
     (#newlines! 2)
   )

2. I suspect the case of two blank lines is going to be quite rare and any more than that will be non-existent. As such, rather than parametrising the hardlines, we can just have a set of captures for appending/prepending a double hardline. For example:

   (
     [
       (some)
       (things)
     ] @append_blankline
     .
     (_)
   )

Option (2) is simpler for the author, but lacks fidelity...but that may not be required.

The only immediate problem I can foresee is what to do in the case when two hardline rules apply in the same position -- say a hardline and a blankline -- which wins? I would say blankline, but for Option (1), the answer is less clear (e.g., max of newlines, sum, etc.).

@tweag/topiary-core-team Any other thoughts?

[arusahni]

I suspect the case of two blank lines is going to be quite rare and any more than that will be non-existent.

The only case for two blank lines I can think of would be with Python, where PEP 8 recommends "Surround top-level function and class definitions with two blank lines."

[Xophmeister]

@arusahni That's the only one I can think of, too. As we're not (currently) attempting to format Python, that amplifies the rarity argument and nudges us towards @{append,prepend}_blankline.

[nbacquey]

It may not even be necessary to introduce a blankline capture: you can emulate it with the append_delimiter capture. Something like the following should probably work:

(
  [
    (some)
    (things)
  ] @append_delimiter
  .
  (_)
  (#delimiter! "\n\n")
)

[Xophmeister]

Good point: This does indeed work 🎉

[tfachmann]

Great! That worked! 🚀

Thank you very much for the active discussion and help, it's highly appreciated