REPL does not consistently process unicode characters in comments.

[Milyardo]

$ cat print.scala
object Test {
  def main(args: Array[String]) = {
    // \u000a System.out.println("Hello World!");
    // \u000d System.out.println("Hello World!");

    // \u000d println("hi")
  }
}

$ scala print.scala
Hello World!
Hello World!
hi

However in the REPL:

$ scala
Welcome to Scala 2.12.4 (GraalVM 1.0.0-rc1, Java 1.8.0_161).
Type in expressions for evaluation. Or try :help.

scala> // \u000a System.out.println("Hello World!");

scala> // \u000d System.out.println("Hello World!");

scala>

Nothing prints.

[SethTisue]

for those who haven't seen it before, the ur-ticket on comments and unicode escapes is #3220

[hrhino]

repl's just too clever by half:

scala> // \u000a System.out.println("Hello World!");

scala> println("I do say: ") // \u000a System.out.println("Hello World!");
I do say:
Hello World!

[hrhino]

ah, my (ancient) quick was 2.13... 2.12 repl is as baffled as I am.

Welcome to Scala 2.12.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_161).
Type in expressions for evaluation. Or try :help.

scala> // \u000a System.out.println("Hello World!")

scala> println("I do say: ") // \u000a System.out.println("Hello World!")
<console>:2: error: illegal start of simple expression
       ;
       ^

[hrhino]

One more datum:

parse("println("I do say: ") // \u000a System.out.println("Hello World!")") Success(List(println("I do say: "), System.out.println("Hello World!")))
[raw] println("I do say: ") // \u000a    <--->   System.out.println("Hello World!")
[adj]    <--->   println("I do say: ") // \u000a System.out.println("Hello World!")
    line: 'println("I do say: ") // \u000a System.out.println("Hello World!")'
 content: 'println("I do say: ") // \u000a System.out.println("Hello World!")'
     was: 'println("I do say: ") // \u000a System.out.println("Hello World!")'
combined: 'val res10 =
println("I do say: ") // \u000a System.out.println("Hello World!")'
parse("val res10 =
println("I do say: ") // \u000a System.out.println("Hello World!")") Success(List(val res10 = println("I do say: "), System.out.println("Hello World!")))
[raw] val res10 =
println("I do say: ") // \u000a    <--->   System.out.println("Hello World!")
[adj] val res10 =
   <--->   println("I do say: ") // \u000a System.out.println("Hello World!")
    line: 'val res10 =
println("I do say: ") // \u000a System.out.println("Hello World!")'
 content: 'val res10 =
println("I do say: ") // \u000a System.out.println("Hello World!")'
     was: 'println("I do say: ") // \u000a System.out.println("Hello World!")'
combined: 'val res10 =
;
val res11 =
println("I do say: ") // \u000a System.out.println("Hello World!")'
<console>:2: error: illegal start of simple expression
       ;
       ^
parse("val res10 =
;
val res11 =
println("I do say: ") // \u000a System.out.println("Hello World!")") Error(List(val res10 = null, val res11 = println("I do say: "), System.out.println("Hello World!")))

so that bug is in the scary line-chopping logic in requestFromLine. (No, I'm not waiting for sbt, why do you ask...)

[SethTisue]

fixed, presumably by @martijnhoekstra's unicode-escape change in 2.13.2