rewrite rules for scala 3 breaks compilation

[mlachkar-da]

Configuration (required)

Please paste the contents of your .scalafmt.conf file here:

version = 3.5.9

project.git = true

align.preset = none # never align to make the fmt more diff friendly
maxColumn = 100
runner.fatalWarnings = true
trailingCommas = multiple
# Disable scala doc wrapping (behavior changed in v3.0.0).
docstrings.wrap = no
newlines.topLevelStatementBlankLines = [
  { blanks { after = 1 }, regex = "^Import" }
]

rewrite.scala3.convertToNewSyntax = true
runner.dialect = "Scala213Source3"

...

Steps

Given code like this:

  def test(instances: String*): Unit = ()

  val a = test("" +: Seq("").map{_ + ""}: _*)

Problem

Scalafmt formats code like this:

  def test(instances: String*): Unit = ()

  val a = test("" +: Seq("").map{_ + ""}*)

Expectation

I expect the code to compile.

[mlachkar-da]

this syntax is not yet allowed on scala213source3 dialect.

[tgodzik]

That's weird, I thought it's supported based on scala/scala#9584

[tgodzik]

It does compile for me 🤔

[mlachkar-da]

you're right!
let me check which scala version I was using

[mlachkar-da]

so it's really a special case:

  val a = test("" +: Seq("").map{_ + ""}: _*)

can you test with that ? it gets rewritte to below, which doesn't compile.

  val a = test("" +: Seq("").map { _ + "" }*)

[tgodzik]

Looks like it should get rewritten to val aaa = test(("" +: Seq("").map{_ + ""})*) with the added parenthesis, but looks like a bug in the compiler.

[mlachkar-da]

I can do a workaround for this, by extracting the value first.

[tgodzik]

That might be a good workaround for now, though we should fix it in scalafmt. I think it might have soemthing to do with operator precedence 🤔

[kitbellew]

scalafmt will not add the parens here, so what's the right solution? not to rewrite this case, keep : _?

[mlachkar-da]

I think it either needs to add the parenthesis, which I think should be the best solution, or at least do nothing.

[tgodzik]

Maybe easiest would be to add parenthesis when infix apply is used?

[kitbellew]

i don't think we have a way (yet) to add anything. we can remove or replace :) i had some code in the works a long time ago, but didn't finish it...