Diverging implicit pprint with Nil or None with default-predef.scala

[lihaoyi]

It seems to work fine when my predef is commented out

haoyi-mbp:Ammonite haoyi$ cat ~/.ammonite/predef.scala
/*load.ivy("com.lihaoyi" %% "ammonite-shell" % ammonite.Constants.version)
@
val shellSession = ammonite.shell.ShellSession()
import shellSession._
import ammonite.shell.PPrints._
import ammonite.ops._
import ammonite.shell._
ammonite.shell.Configure(repl, wd)*/
haoyi-mbp:Ammonite haoyi$ ~/amm
Loading...
Welcome to the Ammonite Repl 0.5.2
(Scala 2.11.7 Java 1.8.0_25)
@ None; Nil
res0_0: None.type = None
res0_1: collection.immutable.Nil.type = List()

But if it's in place, it blows up

haoyi-mbp:Ammonite haoyi$ cat ~/.ammonite/predef.scala
load.ivy("com.lihaoyi" %% "ammonite-shell" % ammonite.Constants.version)
@
val shellSession = ammonite.shell.ShellSession()
import shellSession._
import ammonite.shell.PPrints._
import ammonite.ops._
import ammonite.shell._
ammonite.shell.Configure(repl, wd)
haoyi-mbp:Ammonite haoyi$ ~/amm
Loading...
Welcome to the Ammonite Repl 0.5.2
(Scala 2.11.7 Java 1.8.0_25)
haoyi-Ammonite@ None; Nil
Compilation Failed
Main.scala:154: diverging implicit expansion for type pprint.PPrinter[A]
starting with method pathRepr in object PPrints
              .print(res0_0, res0_0, "res0_0", scala.None)
                    ^

Clearly some implicit in the default predef is messing with things.

[lihaoyi]

Here's a smaller repro, with no predef

haoyi-mbp:Ammonite haoyi$ ~/amm
Loading...
Welcome to the Ammonite Repl 0.5.2
(Scala 2.11.7 Java 1.8.0_25)
@ None
res0: None.type = None
@ implicit def foo: pprint.PPrinter[java.io.File] = ???
defined function foo
@ None
Compilation Failed
Main.scala:49: diverging implicit expansion for type pprint.PPrinter[A]
starting with method foo in object cmd1
              .print(res2, res2, "res2", scala.None)
                    ^

wtf?

[winitzki]

Another comment: the problem occurs only when None is not explicitly typed (of type None.type).

@ val x : Option[Int] = None
x: Option[Int] = None
@ x
res1: Option[Int] = None
@ None
cmd2.sc:8: diverging implicit expansion for type pprint.PPrinter[A]
starting with method lsSeqRepr in object PPrints
            .print(res2, res2, "res2", _root_.scala.None)
                  ^
Compilation Failed

[DavidPerezIngeniero]

I'm having the same error!

[lihaoyi]

Should be fixed in 2d78e1f, which uses the new version of pprint which no longer uses macros/implicits