xdebug_call_class, xdebug_call_file, and xdebug_call_function could be improved by allowing for an arguement to skip back a few steps.

IE instead of having to add calls at every point in every file where you want the caller info such as
$callFile = xdebug_call_file();
$callLine = xdebug_call_line();
$callClass = xdebug_call_class();

An easier option would be to declare a single function:
function dumpCaller($i = 0) {
$callFile = xdebug_call_file($i);
$callLine = xdebug_call_line($i);
echo "Called from $callLine in $callFile";
}

Allowing for multiple steps would allow using it in a code profiler, such as the common:

if {$profileFlag) {
ProfileClass::start();
}

Then if the start method, a call to dumpCaller with an argument of 2 would allow a backstep into the actual callee to find the actual caller.