module foo.bar;

import core.exception;
import std.stdio;

void main()
{
    try
    {
        assert(0);
    }
    catch (Throwable e)
    {
        writeln(e.file);
    }

    try
    {
        throw new Exception("");
    }
    catch (Throwable e)
    {
        writeln(e.file);
    }
}

$ rdmd test.d

foo.bar
test.d

The assert sets the 'file' field to the module name, whereas an Exception sets it to the file name. This makes it hard to parse the file field in order to produce error messages which can further be parsed by e.g. editors or IDE tools (for example double-click on a unittest failure message could automatically open a file, *if* the path is actually valid).