Re: Weird exit caused in a trap DEBUG which sources a file.

["Rocky Bernstein" <rocky.bernstein@xxxxxxxxx>]

Comments in line.

On Fri, Aug 1, 2008 at 9:37 AM, Peter Stephenson <pws@xxxxxxx> wrote:
> On Fri, 1 Aug 2008 08:29:29 -0400
> "Rocky Bernstein" <rocky.bernstein@xxxxxxxxx> wrote:
>> Looks like the crucial change that makes zsh 4.3.5-dev and current SVN
>> sources fail is an extra source after the trap DEBUG:
>
> Thanks, this is what I needed.

No, thank you! I just tried the patch and it works fine.

So there's no mystery. I've been porting the bash debugger code to
zsh. So far, print/eval, stepping and some stack frame commands work.
But this is far from ready for general consumption.

Part of this is a more general effort at writing about POSIX shells
which I give maybe a 50% chance of happening.

>
> The source code wasn't handling the variable that indicates a trap has told
> us to return from a function properly.  The variable is only primed for
> action if negative.  That's the init.c hunk.
>
> The signals.c hunk is to save and restore trapreturn for nested trap
> handlers.  I'm not sure it's necessary; I am sure it's not wrong and
> prevents hostages to fortune.

Not sure the additional code is necessary or that nested trap handlers
are necessary?  I'm pretty sure you mean the former. Nested trap
handlers are useful.

>
> The hairy trap tests still pass, which is good; it would be better to add
> this as a test, too, which shouldn't be too hard as there's nothing here
> that depends on external behaviour.
>
> I've documented the variable trapreturn better.

Thanks. It seems weird that trapreturn is is initialised to -1 for a
function trap and
 -2 for a non-function trap and decremented for subsequent function
calls. Because this means that trapreturn for a for a function trap
that calls a function would have the same value as for a non-function
trap.


>
> Index: Src/exec.c
> ===================================================================
> RCS file: /cvsroot/zsh/zsh/Src/exec.c,v
> retrieving revision 1.135
> diff -u -r1.135 exec.c
> --- Src/exec.c  31 Jul 2008 08:44:21 -0000      1.135
> +++ Src/exec.c  1 Aug 2008 13:29:06 -0000
> @@ -64,7 +64,23 @@
>  /**/
>  mod_export int errflag;
>
> -/* Status of return from a trap */
> +/*
> + * Status of return from a trap.
> + * This is only active if we are inside a trap, else its value
> + * is irrelevant.  It is initialised to -1 for a function trap and
> + * -2 for a non-function trap and if negative is decremented as
> + * we go deeper into functions and incremented as we come back up.
> + * The value is used to decide if an explicit "return" should cause
> + * a return from the caller of the trap; it does this by setting
> + * trapreturn to a status (i.e. a non-negative value).
> + *
> + * In summary, trapreturn is
> + * - zero unless we are in a trap
> + * - negative in a trap unless it has triggered.  Code uses this
> + *   to detect an active trap.
> + * - non-negative in a trap once it was triggered.  It should remain
> + *   non-negative until restored after execution of the trap.
> + */
>
>  /**/
>  int trapreturn;
> Index: Src/init.c
> ===================================================================
> RCS file: /cvsroot/zsh/zsh/Src/init.c,v
> retrieving revision 1.87
> diff -u -r1.87 init.c
> --- Src/init.c  31 Jul 2008 08:44:21 -0000      1.87
> +++ Src/init.c  1 Aug 2008 13:29:06 -0000
> @@ -191,7 +191,7 @@
>            exit(lastval);
>        if (((!interact || sourcelevel) && errflag) || retflag)
>            break;
> -       if (trapreturn) {
> +       if (trapreturn >= 0) {
>            lastval = trapreturn;
>            trapreturn = 0;
>        }
> Index: Src/signals.c
> ===================================================================
> RCS file: /cvsroot/zsh/zsh/Src/signals.c,v
> retrieving revision 1.47
> diff -u -r1.47 signals.c
> --- Src/signals.c       31 Jul 2008 08:44:21 -0000      1.47
> +++ Src/signals.c       1 Aug 2008 13:29:06 -0000
> @@ -1085,6 +1085,7 @@
>     int trapret = 0;
>     int obreaks = breaks;
>     int oretflag = retflag;
> +    int otrapreturn = trapreturn;
>     int isfunc;
>     int traperr;
>
> @@ -1183,6 +1184,7 @@
>        trapret = trapreturn + 1;
>     }
>     traperr = errflag;
> +    trapreturn = otrapreturn;
>     execrestore();
>     lexrestore();
>
>
> --
> Peter Stephenson <pws@xxxxxxx>                  Software Engineer
> CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
> Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070
>