Backport tools.jar robustness for REPL, fail loud

[scabug]

After launching the REPL from sbt, the :javap command does not work for class names:

scala> :javap iControl.services.CommonIPPortDefinition

scala> :javap iControl.services.CommonIPPortDefinition

scala> :javap java.lang.Object

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7652?orig=1
Reporter: Robin Green (greenrd)
Affected Versions: 2.10.0, 2.10.1, 2.10.2

[scabug]

Robin Green (greenrd) said:
Scala 2.9.1 prints:

:javap unavailable on this platform.

[scabug]

Robin Green (greenrd) said:
Workaround:

scala -toolcp /usr/lib/jvm/jdk1.6.0_32/lib/tools.jar

However, it doesn't look like I can use this workaround from sbt.

[scabug]

@som-snytt said:
IIUC, this is a request to backport a fix in 2.10 to search for tools.jar.

IOW, this works in 2.10, and "affects versions" is only 2.9.

https://github.com/scala/scala/blob/v2.10.2/src/compiler/scala/tools/nsc/interpreter/ILoop.scala#L376

[scabug]

Robin Green (greenrd) said:
No, it doesn't work in 2.10. The command prints nothing. In Scala 2.9, it at least prints an error message, but it doesn't find the tools.jar in either version.

[scabug]

@som-snytt said:
I left my comfort zone and got the versions aligned, but alas IWFM on 2.10.

There was an enhancement for 2.11:

#7410

On Ubuntu it's easy to get JAVA_HOME, java and javac at cross-purposes. In my case, after installing jdk7, it left java at java6. I've forgotten the details except that it was a confusing mode of failure; perhaps it's more confusing on 2.10.

apm@mara:~/tmp/q$ JAVA_HOME=$JAVA6_HOME sbt12
[info] Set current project to default-7bbd7f (in build file:/home/apm/tmp/q/)
> ++ 2.10.2
Setting version to 2.10.2
[info] Set current project to default-7bbd7f (in build file:/home/apm/tmp/q/)
> console
[info] Updating {file:/home/apm/tmp/q/}default-7bbd7f...
[info] Resolving org.scala-lang#scala-library;2.10.2 ...
[info] Done updating.
[info] 'compiler-interface' not yet compiled for Scala 2.10.2. Compiling...
[info]   Compilation completed in 12.899 s
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.10.2 (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :javap
:javap [-lcsvp] [path1 path2 ...]

scala> :javap -public scala.Option
Compiled from "Option.scala"

I see there's an about command:

> about
[info] This is sbt 0.12.3
[info] The current project is {file:/home/apm/tmp/q/}default-7bbd7f
[info] The current project is built against Scala 2.10.2
[info] 
[info] sbt, sbt plugins, and build definitions are using Scala 2.9.2
> 

There's a debug flag that might help. But what does this mean?

$ sbt12 -Dscala.repl.debug=true

Welcome to Scala version 2.10.2 (OpenJDK 64-Bit Server VM, Java 1.7.0_25).
Type in expressions to have them evaluated.
Type :help for more information.
[info] started at Thu Aug 29 11:21:32 PDT 2013

scala> :javap
:javap unavailable: no tools.jar at /usr/lib/jvm/java-7-openjdk-amd64
:javap not yet working with java 1.7

Not finding tools.jar should be a spurious report.

Running that again with JDK 6 works as expected:

Welcome to Scala version 2.10.2 (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.
[info] started at Thu Aug 29 11:28:58 PDT 2013

scala> :javap
:javap available.
:javap [-lcsvp] [path1 path2 ...]

scala> :javap java.lang.Object
Compiled from "Object.java"

Also, under debug,

> about
[info] This is sbt 0.12.3
[info] The current project is {file:/home/apm/tmp/q/}default-7bbd7f
[info] The current project is built against Scala 2.9.2
[info] 
[info] sbt, sbt plugins, and build definitions are using Scala 2.9.2
> console
[info] Starting scala interpreter...
[info] 
[error] (run-main) java.lang.NullPointerException
java.lang.NullPointerException
	at scala.tools.nsc.interpreter.ILoop.<init>(ILoop.scala:68)
	at scala.tools.nsc.InterpreterLoop.<init>(InterpreterLoop.scala:9)
	at scala.tools.nsc.InterpreterLoop.<init>(InterpreterLoop.scala:11)
	at xsbt.ConsoleInterface$$anon$1.<init>(ConsoleInterface.scala:27)
	at xsbt.ConsoleInterface.run(ConsoleInterface.scala:27)

[scabug]

@som-snytt said:
Yes, that seems to be the problem, viz, java and JAVA_HOME do not jibe.

I was able to test this way, without munging my environment, thankfully. This is java at v6 and JAVA_HOME at v7; reflective invocation of javap finds the wrong tools.jar.

apm@mara:~/tmp/q$ JAVACMD=$JAVA6_HOME/bin/java JAVA_HOME=$JAVA7_HOME sbt12 
Launching with /home/apm/bin/sbt-0.12.3/bin/sbt-launch.jar
[info] Set current project to default-7bbd7f (in build file:/home/apm/tmp/q/)
> 
> ++ 2.10.2
Setting version to 2.10.2
[info] Set current project to default-7bbd7f (in build file:/home/apm/tmp/q/)
> 
> about
[info] This is sbt 0.12.3
[info] The current project is {file:/home/apm/tmp/q/}default-7bbd7f
[info] The current project is built against Scala 2.10.2
[info] 
[info] sbt, sbt plugins, and build definitions are using Scala 2.9.2
> console
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.10.2 (OpenJDK 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :javap
:javap [-lcsvp] [path1 path2 ...]

scala> :javap java.lang.Object

scala> 

It does indeed fail silently. Boy, that's confusing.

[scabug]

@som-snytt said:
Let it never be said that :javap command does nothing.

scala/scala#2895