Rescript formatter incorrectly moves comments

[siddharth-krishna]

The rescript formatter incorrectly moves comments out of the block/function that they are in. For example,

doSomething()
->Js.Promise.then_(
  result =>
    // Comment 1
    switch result {
    | Some(y) =>
      // Comment 2
      something()
      // Comment 3
      somethingElse()
    | None => ()
    },
  _,
)

becomes

doSomething()->Js.Promise.then_(
  result =>
    switch result {
    | Some(y) =>
      something()

      somethingElse()
    | None => ()
    },
  // Comment 1

  // Comment 2

  // Comment 3

  _,
)

Rescript and the formatter are awesome! But this issue is one of the last few blockers to adding the formatter to our pre-commit / PR process..

Rescript version: 10.0.1
VS Code extension: v1.6.0

[cristianoc]

Cut-down example:

foo(
  // Comment 1
  switch result {
  | Some(y) =>
    // Comment 2
    something()
    // Comment 3
    somethingElse()
  | None => ()
  },
  _,
)

Do you have a smaller example too? It's definitely about underscore _, not sure if the switch is relevant.

[siddharth-krishna]

foo(
  // Comment 1
  x => {
    // Comment 2
    something()
  },
  _,
)

[cristianoc]

So it's definitely about the _ transformation.
What it does is:

__x =>
foo(
  // Comment 1
  x => {
    // Comment 2
    something()
  },
  __x,
)

which by itself is OK if done ahead of time, but seems to interfere with the locations for formatting.

Written by hand as above, it formats to:

foo(// Comment 1
x => {
  // Comment 2
  something()
}, _)

which subsequently formats to:

foo(
  x => {
    something()
  },
  // Comment 1

  // Comment 2

  _,
)

so the example would also fail the roundtrip test (formatting the second time should make no difference).

So the transformation performed internally is not equivalent to what one would write by hand, in some respect.

[cristianoc]

Done

[siddharth-krishna]

Wow, that was quick! Thank you :)