Implement :settings in the REPL

[dwijnand]

No description provided.

[dwijnand]

@griggt @som-snytt do either (or both!) of you want to help review and merge this, please?

[dwijnand]

• Does :reset clear the settings in Scala 2? Because I think it does in this implementation.

[som-snytt]

I don't remember the behavior of :reset except that there is a ticket about reset not resetting enough. The big feature is to collect bindings. I've forgotten what else was not reset. :replay -Xlint was the useful "once more with these settings". I guess I would expect reset to restore settings to defaults. What are the defaults? It was -deprecation -feature unless there are explicit settings.

[som-snytt]

An essential command! Puts the REPL on a firm setting.

[dwijnand]

I guess I would expect reset to restore settings to defaults.

Well that makes it harder, because it actually doesn't:

Welcome to Scala 2.13.7 (OpenJDK 64-Bit Server VM, Java 1.8.0_282).
Type in expressions for evaluation. Or try :help.

scala> :settings
-Vbrowse = List()
-Vprint = List()
-Vtyper = false
-Wconf = List(cat=feature:w, cat=deprecation:w, cat=deprecation:ws, cat=feature:ws, cat=optimizer:ws)
-Xmaxwarns = 100
-deprecation = true
-encoding = UTF-8
-feature = true
-nowarn = false

scala> :settings -Xsource:3

scala> :settings
-Vbrowse = List()
-Vprint = List()
-Vtyper = false
-Wconf = List(cat=feature:w, cat=deprecation:w, cat=deprecation:ws, cat=feature:ws, cat=optimizer:ws)
-Xmaxwarns = 100
-Xsource = SpecificScalaVersion(3,0,0,Final)
-deprecation = true
-encoding = UTF-8
-feature = true
-nowarn = false

scala> :reset
Resetting REPL state.
Forgetting all expression results and named terms: $intp

scala> :settings
-Vbrowse = List()
-Vprint = List()
-Vtyper = false
-Wconf = List(cat=feature:w, cat=deprecation:w, cat=deprecation:ws, cat=feature:ws, cat=optimizer:ws)
-Xmaxwarns = 100
-Xsource = SpecificScalaVersion(3,0,0,Final)
-deprecation = true
-encoding = UTF-8
-feature = true
-nowarn = false

What are the defaults? It was -deprecation -feature unless there are explicit settings.

Yeah, it's not that in Scala 3. But I wouldn't be against someone proposing that change.

[som-snytt]

Thanks for the tweak (to the code).

If I didn't mention, I noticed that some settings are cached so setting in Scala 2 repl doesn't take. :se -Vprint:typer but not :se -Vtyper for example. You have to restart in that case.

[dwijnand]

@griggt happy for this to land or do you still want to look at it first?

[griggt]

I should have time tomorrow to review in more detail. Some initial comments:

• it would be nice to add :settings to the REPL :help display
• is the behavior shown below expected?

$ mkdir -p /tmp/{a,b}

$ ./bin/scala
scala> :settings -d /tmp/a

scala> val x = 42
val x: Int = 42

scala> class Foo
// defined class Foo

$ ./bin/scala
scala> val x = 42
val x: Int = 42

scala> :settings -d /tmp/b

scala> class Foo
Exception in thread "main" java.lang.ClassNotFoundException: repl$.rs$line$2$
	at dotty.tools.repl.AbstractFileClassLoader.findClass(AbstractFileClassLoader.scala:49)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
	at dotty.tools.repl.AbstractFileClassLoader.loadClass(AbstractFileClassLoader.scala:55)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:348)
	at dotty.tools.repl.Rendering.load$1(Rendering.scala:147)
	at dotty.tools.repl.Rendering.forceModule(Rendering.scala:149)
	at dotty.tools.repl.ReplDriver.extractAndFormatMembers$1(ReplDriver.scala:328)
	at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:349)
	at scala.Option.map(Option.scala:242)
	at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:352)
	at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:271)
	at scala.util.Either.fold(Either.scala:189)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:287)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:221)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:155)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:158)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:177)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:158)
	at dotty.tools.repl.ReplDriver.tryRunning(ReplDriver.scala:120)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.MainGenericRunner$.run$1(MainGenericRunner.scala:177)
	at dotty.tools.MainGenericRunner$.main(MainGenericRunner.scala:239)
	at dotty.tools.MainGenericRunner.main(MainGenericRunner.scala)

[dwijnand]

Som the magician foresaw it: some settings are cached (like outputDir in the REPL rendering classloader).

[dwijnand]

Needed this again, today (wanted to see -explain in the REPL) and didn't realise it still wasn't in the nightlies.