Details
-
Type:
Bug
-
Status:
Resolved
-
Priority:
Major
-
Resolution: Fixed
-
Affects Version/s: JRuby 1.6.7
-
Fix Version/s: JRuby 1.7.0.pre1
-
Component/s: Core Classes/Modules
-
Labels:None
-
Patch Submitted:Yes
-
Number of attachments :
Description
When you use RubyException.printBacktrace to print out an exception, the first line of the backtrace is omitted. See attached patch. I wondered whether this was deliberate, but I struggle to see why one wouldn't want to see the first line.
Activity
My use case: I have a Ruby class that implements a Java interface. The interface specifies that methods should throw a particular Java exception, but the underlying Ruby code throws a Ruby exception, and I want to preserve the Ruby backtrace information for easier debugging. So I have a wrapper that translates from Ruby exceptions to Java exceptions, like this:
public interface MyInterface {
void foo() throws MyException;
}
class MyException extends Exception {
private String backtrace;
public MyException(RubyException cause) {
this.backtrace = ???; // how do I format cause's exception nicely as a string?
}
public String getBacktrace() {
return backtrace;
}
}
# In Ruby:
class MyImplementation
include Java::MyInterface
def foo
# do stuff
rescue => e
raise Java::MyException.new(e)
end
end
I was originally using RubyException.printBacktrace (with a PrintStream based on ByteArrayOutputStream) to generate the string representation of the Ruby backtrace (the ??? place above).
However, with the first line missing, the backtrace wasn't very useful. 
So instead I'm now iterating over the backtrace lines returned by RubyException.getBacktrace(), and constructing the string myself. That's actually quite reasonable.
It appears to me that the only case where this makes a difference is when we raise an non-NativeException exception while backtrace style is 'mri'.
As you can see below, the first element of the backtrace is a rather ugly duplicate. So it seems OK for me to skip it. Why this is the case, I have not investigated.
The short of it, though, is that this appears to be a WONTFIX.
Here is the comparison for the backtrace:
I tracked this down to this commit: https://github.com/jruby/jruby/commit/53278235b77a3297d5e7d9cc2642d45edf7a6821