int foo(int x)
in {
    assert(x >= 0); // line 3.
} body {
    return x ^^ 2;
}
void main() {
    foo(-1); // line 8.
}


With DMD 2.064alpha it gives at run-time:

core.exception.AssertError@temp(3): Assertion failure

followed by the stack trace.


To speed up my debugging I suggest to instead generate two error messages similar to (the second line is the same as before):

temp.d(8): Pre-condition violation: x >= 0  (x = -1)
core.exception.AssertError@temp(3): Assertion failure