trailing comma support - "Expected identifier, but got Token(RPAREN,),xxx,))

[marekzebrowski]

linked issue with reproducer scalastyle/scalastyle#276
even simpler example of valid scala 2.12 code

case class A(i:Int,
)

is not parsed correctly

[godenji]

For everyone who thumbs up'd this issue the companion PR won't get merged until there's some test coverage that verifies trailing commas work as expected (and don't break existing tests).

A simple test implementation might look like this.

[c-dante]

I made a parser spec that the PR fails on -- working on a fix that supports http://docs.scala-lang.org/sips/completed/trailing-commas.html

TL;DR: https://github.com/c-dante/scalariform/tree/260-trailing-comma
Current way the parser/lexer work seems it won't allow a nice way to accommodate trailing commas with formatting intents. Debating what to do to support this.

Edit:
Seems this issue is going to be annoying to fix for only the allowed cases, since you want to know what your terminal token is -- inParens, inBrackets, and inBraces don't know if they allow trailing --- tokenSeparated can know if it allows trailing, and allow the R* cases if true, but that feels loose.

Edit2:
Further complicated because this is valid:

Seq(1,
)

However this is not: Seq(1,)

Which the current lexer setup doesn't allow checking for

Edit3:
Further still, the current way of representing token expressions in the parser prevents a setting to control intent-based handling. This is a similar setting to dangling parenthesis setting.

[godenji]

fixed in #262