[Issue 15894] New: Allow setting of rt_trapExceptions from module c'tors

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15894

          Issue ID: 15894
           Summary: Allow setting of rt_trapExceptions from module c'tors
           Product: D
           Version: D2
          Hardware: x86_64
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: dmdtracker at supradigital.org

If you want a proper core dump upon an assert failure (or generally a uncaught
exception), you have to set rt_trapExceptions to 0. 

You can't do that however without either compiling your own runtime or
attaching a debugger and setting it from there before main() is called.

While you can change the variable (as it is a global extern (C), your change
has no effect because all user code is run only after the variable has been
read.

This PR changes the behavior so that changes to that variable done from a
module c'tor will cause your main() to be called without the exception trap:

https://github.com/D-Programming-Language/druntime/pull/1538

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