REPL: JLine 3: bring back -Xnojline, but deprecate it

[SethTisue]

instead, -Xjline:off is now recommended

fixes scala/scala-dev#694

[SethTisue]

the deprecation doesn't actually cause a warning to be printed when the REPL starts, so that part is mostly an empty gesture, but it's still worth doing to keep it from showing up on the compiler options doc page, I think

[som-snytt]

I'd swear Grigolo as Cavaradossi just looked at Scarpia and they went, Don't make me laugh!, for a second. Now Yoncheva's Floria ("Flo") Tosca has just arrived at Scarpia's.

As with Scarpia, I can't really approve.

[dwijnand]

the deprecation doesn't actually cause a warning to be printed when the REPL starts, so that part is mostly an empty gesture, but it's still worth doing to keep it from showing up on the compiler options doc page, I think

I feel like that should change, no? How many other warnings are we/users not seeing?

[dwijnand]

Another example:

$ scala -2.13.head -deprecation -Xsource:2.14 -e 'class C'
warning: -Xsource is deprecated: instead of -Xsource:2.14, use -Xsource:3

$ scala -2.13.head -deprecation -Xsource:2.14
Welcome to Scala 2.13.2-bin-8de6e34 (OpenJDK 64-Bit Server VM, Java 11.0.6).
Type in expressions for evaluation. Or try :help.

scala>

(edit: that warning message isn't the best, I just realised.)

[lrytz]

If I remember correctly, deprecation warnings for compiler flags are printed at the end of the compiler Run, so in the repl they would be printed after each line. I guess that's why they were disabled, we could instead print them after the repl initialization.

[dwijnand]

Oh, yeah:

$ scala -2.13.head -deprecation -Xsource:2.14
Welcome to Scala 2.13.2-bin-8de6e34 (OpenJDK 64-Bit Server VM, Java 11.0.6).
Type in expressions for evaluation. Or try :help.

scala> 1
warning: -Xsource is deprecated: instead of -Xsource:2.14, use -Xsource:3
val res0: Int = 1

scala>
:quit
$ scala -2.13.head -Xnojline -deprecation
Welcome to Scala 2.13.2-bin-8de6e34 (OpenJDK 64-Bit Server VM, Java 11.0.6).
Type in expressions for evaluation. Or try :help.

scala> 1
warning: -Xnojline is deprecated: Replaced by -Xjline:off
val res0: Int = 1

scala> :quit