The first part of solving the problem was to look for clues in the Problems view. Opening it, I saw this:

error while loading Configgy, Scala signature Configgy has wrong version expected: 5.0 found: 4.1 in /Users/…

So the first error was due to the compilation failing and not producing a main class that eclipse could launch.

After further digging, the version error turned out to be caused by a mismatch between the Scala version (2.7.5) I used to compile the Configgy library and the Scala version (2.8) that the eclipse plugin used to compile the rest of the program. I didn’t install Scala 2.8, so how could this occur? The Scala plugin installs its own version of Scala. Because I had selected the nightly build version of the plugin, the Scala versions drifted apart during one of the eclipse updates.

You can tell which version the eclipse Scala plugin uses by looking at the jar name in the eclipse/plugins directory. Eg, scala.tools.nsc_2.75.final.jar

The solution was to revert to the stable, release version of the plugin. Do that by using this url in the eclipse Software Updates | Available Software | Manage Sites… list.

http://www.scala-lang.org/scala-eclipse-plugin

More complete directions here.

$ sudo port install git

Then clone the Configgy repository with

$ git clone git://github.com/robey/configgy.git

Then cd into the top-level directory and build as described below.

When you want to update, just pull the latest changes and rebuild.

$ git pull
$ ant clean; ant package

Note that ant package may be particular to Configgy. Sometimes just ant is sufficient and will use the defaults.

To install, just download and, in its directory, type

$ant package

( The ‘$’ is your terminal command-line prompt. Don’t type it.)

If you see the following errors:

[scalac] Compiling 16 source files to /Users/Gary/Development/scala/configgy/target/classes
[scalac] /Users/Gary/Development/scala/configgy/src/main/scala/net/lag/configgy/JMXWrapper.scala:51: error: wrong number of arguments for constructor MBeanInfo: (java.lang.String,java.lang.String,Array[javax.management.MBeanAttributeInfo],Array[javax.management.MBeanConstructorInfo],Array[javax.management.MBeanOperationInfo],Array[javax.management.MBeanNotificationInfo])javax.management.MBeanInfo
[scalac] new jmx.MBeanInfo(”net.lag.configgy.ConfigMap”, “configuration node”, node.asJmxAttributes(),
[scalac] ^
[scalac] /Users/Gary/Development/scala/configgy/src/main/scala/net/lag/configgy/JMXWrapper.scala:115: error: value asList is not a member of javax.management.AttributeList
[scalac] for (attr <- jcl.Buffer(attrs.asList)) setAttribute(attr)
[scalac] ^
[scalac] two errors found

…it’s because Configgy requires Java 1.6. You probably haven’t set your JAVA_HOME and are defaulting to Java 1.5. To correct your environment variables on the Mac, see my notes below.

Next, if you’re trying out the example code and see an error like:

Compiling 1 source file to /Users/Gary/Development/NetBeansProjects/ScalaApplication1/build/classes
/Users/Gary/Development/NetBeansProjects/ScalaApplication1/src/scalaapplication1/Main.scala:27: error: value get is not a member of net.lag.configgy.Config
val hostname = config.get(”hostname”, “localhost”)

…it’s because that function has been renamed getString(), but not all of the documentation has been updated. Change it to:

val hostname = config.getString(”hostname”, “localhost”)