Port upgrade for cmake failed

[Chris Scharver]

>> $ sudo port -d upgrade cmake
>> .
>> -- Java version 1.6.0.22 configured successfully!
>> CMake Error at Tests/CMakeLists.txt:1630 (FILE):
>> file Internal CMake error when trying to open file:
>> /System/Library/Frameworks/JavaVM.framework/Headers/jni.h for reading.
> 
> It has already been filed:
> http://trac.macports.org/ticket/26934

So I'm trying to check whether that jni header exists prior to running the port's configure phase. I am able to detect it's missing, and I trigger a ui_error. Unfortunately, that doesn't halt the configure phase. I expected ui_error to stop the current phase and report the message, not continue onward.

platform darwin {
	pre-configure {
		if {![file exists "/System/Library/Frameworks/JavaVM.framework/Headers/jni.h"]} {
			ui_error "${name} requires the that the Java for Mac OS X Developer Package is installed. Please download and install this package from http://developer.apple.com/."
		}
	}
	...

What's the best way for me to immediately halt the current phase?

Thanks,
Chris