Re: Extended Exceptions and other tweaks.

[Brian Drummond <brian@shapes.demon.co.uk>]

On Wed, 01 May 2013 20:06:20 -0500, Randy Brukardt wrote:

> "Brian Drummond" <brian@shapes.demon.co.uk> wrote in message
> news:kls8v6$70i$1@dont-email.me...
> ...
>> So the following ,
>>
>> raise Timer_A.oops; -- last chance handler!
>> and use Timer_A;
>> raise oops; -- can be locally handled
>>
>> end up in different exception handlers!
>>
>> I'm not clear on whether this is expected behaviour...
> 
> It's certainly not Ada behavior. 

I have failed to reproduce that one with the native compiler...
However I did find this interesting specimen: (source below)

The compiler apparently agrees with my understanding of 
"pragma Restrictions (No_Exception_Propagation)" which is:
Immediately local exception handler is allowed;
Last chance handler is allowed; (and raising another exception in "doit2" 
will indeed reach the Last chance handler)
Anything in between is (a) not permitted and (b) will not run...

gnatmake -gnatwa -gnatw.x test_eh.adb
gcc -c -gnatwa -gnatw.x test_eh.adb
test_eh.adb:16:07: warning: pragma Restrictions 
(No_Exception_Propagation) in effect
test_eh.adb:16:07: warning: execution may raise unhandled exception
test_eh.adb:27:04: warning: pragma Restrictions 
(No_Exception_Propagation) in effect
test_eh.adb:27:04: warning: this handler can never be entered, and has 
been removed

but the resulting executable does not...

./test_eh
Main program start
Local handler : oops!
Second try
No_Exception_Propagation: this cannot happen...

Now is there a reasonable explanation that I have missed, or is this 
worth reporting as a compiler bug?

- Brian



Compiler versions:
FSF Gnat 4.6.3, 4.7.2
GNATMAKE GPL 2011 (20110419)

Source :
--------------------------------------------------------------------
pragma Restrictions (No_Exception_Propagation);

with Ada.Text_IO;  use Ada.Text_IO;

procedure Test_EH is

   Oops : exception;

   procedure doit is begin
      raise Oops;
   exception
      when Oops => Ada.Text_IO.Put_Line("Local handler : oops!");
   end doit;

   procedure doit2 is begin
      raise Oops;   -- line 16
      -- raise Program_Error;
   end doit2;
 
begin
   Ada.Text_IO.Put_Line("Main program start");
   doit;
   Ada.Text_IO.Put_Line("Second try");
   doit2;
   Ada.Text_IO.Put_Line("Main program done");
exception
   when Oops => Ada.Text_IO.Put_Line  -- line 27
        ("No_Exception_Propagation: this cannot happen...");
end Test_EH;
--------------------------------------------------------------------