When trying to debug issues like  bug 656717 , there is no useful output from the java compilation stage run by utils/compile_gwt_clients.py. This is because compiles are done with utils.run() in compile_and_install_client().

Instead of this:

utotest-web-frontend-0.0.1-r1449: 08:48:03 DEBUG| Running 'java  -Xmx512M -Djava.util.prefs.userRoot=/tmp -cp "/build/guado_moblab/tmp/portage/chromeos-base/autotest-web-frontend-0.0.1-r1449/work/autotest-work/frontend/client/src:/build/guado_moblab/tmp/portage/chromeos-base/autotest-web-frontend-0.0.1-r1449/work/autotest-work/frontend/client/bin:/opt/google-web-toolkit/gwt-user.jar:/opt/google-web-toolkit/gwt-dev.jar" -Djava.awt.headless=true com.google.gwt.dev.Compiler -war "/build/guado_moblab/tmp/portage/chromeos-base/autotest-web-frontend-0.0.1-r1449/work/autotest-work/frontend/client/www.new" autotest.MoblabSetupClient'
autotest-web-frontend-0.0.1-r1449: 08:48:17 ERROR| Error compiling autotest.MoblabSetupClient, leaving old client


We should get an actual Java compilation error, like:

14:35:05 ERROR| [stderr] Exception in thread "Thread-3" java.lang.UnsatisfiedLinkError: /opt/icedtea-bin-7.2.5.3/jre/lib/amd64/headless/libmawt.so: libcups.so.2: cannot open shared object file: No such file or directory
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader$NativeLibrary.load(Native Method)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary1(ClassLoader.java:1965)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1890)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1851)
14:35:05 ERROR| [stderr] 	at java.lang.Runtime.load0(Runtime.java:795)
14:35:05 ERROR| [stderr] 	at java.lang.System.load(System.java:1062)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader$NativeLibrary.load(Native Method)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary1(ClassLoader.java:1965)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1890)
14:35:05 ERROR| [stderr] 	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1872)
14:35:05 ERROR| [stderr] 	at java.lang.Runtime.loadLibrary0(Runtime.java:849)
14:35:05 ERROR| [stderr] 	at java.lang.System.loadLibrary(System.java:1088)
14:35:05 ERROR| [stderr] 	at sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:77)
14:35:05 ERROR| [stderr] 	at java.security.AccessController.doPrivileged(Native Method)
14:35:05 ERROR| [stderr] 	at sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:74)
14:35:05 ERROR| [stderr] 	at java.lang.Class.forName0(Native Method)
14:35:05 ERROR| [stderr] 	at java.lang.Class.forName(Class.java:191)
14:35:05 ERROR| [stderr] 	at java.awt.GraphicsEnvironment.createGE(GraphicsEnvironment.java:102)
14:35:05 ERROR| [stderr] 	at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:81)
14:35:05 ERROR| [stderr] 	at com.google.gwt.dev.Precompile$GraphicsInitThread.run(Precompile.java:325)

So far, just using utils.system() instead gives a *lot* of probably-unhelpful DEBUG prints (stdout) too.