[BUG] ignored trap and subshell

[BUG] ignored trap and subshell

[Vincent Lefevre]

The zshmisc(1) man page says:

    ( list )
        Execute list in a subshell.  Traps set by the trap builtin are
        reset to their default values while executing list.

However, with "emulate sh", ignored traps should still be ignored
in the subshell according to POSIX, and zsh 5.8 fails do conform:

$ zsh -c 'emulate sh; trap "" INT; trap; echo A; ( trap; echo B; sleep 3; ); echo $?'
trap -- '' INT
A
B
^C130

where Ctrl-C immediately interrupts the sleep.

Compare to sh:

$ sh -c 'trap "" INT; trap; echo A; ( trap; echo B; sleep 3; ); echo $?'
trap -- '' INT
A
trap -- '' INT
B
^C0

where the sleep isn't interrupted by Ctrl-C.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Re: [BUG] ignored trap and subshell

[Bart Schaefer]

On Tue, Aug 24, 2021 at 9:24 AM Vincent Lefevre <vincent@vinc17.net> wrote:
>
> However, with "emulate sh", ignored traps should still be ignored
> in the subshell according to POSIX, and zsh 5.8 fails do conform:

"emulate sh" is NOT the same as "ARGV0=sh", and is never going to be.
We make no representation that "emulate sh" will enable all the same
standards behaviors as using "sh" as the command name.

That said, it might be possible to add control of this behavior to the
POSIX_TRAPS option, in which case it would be covered by "emulate sh".

Re: [BUG] ignored trap and subshell

[Bart Schaefer]

On Tue, Aug 24, 2021 at 10:29 AM Bart Schaefer
<schaefer@brasslantern.com> wrote:
>
> On Tue, Aug 24, 2021 at 9:24 AM Vincent Lefevre <vincent@vinc17.net> wrote:
> >
> > However, with "emulate sh", ignored traps should still be ignored
> > in the subshell according to POSIX, and zsh 5.8 fails do conform:
>
> "emulate sh" is NOT the same as "ARGV0=sh", and is never going to be.

However, it appears this behavior isn't covered in regular sh emulation either:

% ARGV0=sh Src/zsh -c 'trap "" INT; trap; echo A; ( trap; echo B;
sleep 3; ); echo $?'
trap -- '' INT
A
B
^C130

So we should look into this.

Re: [BUG] ignored trap and subshell

[Peter Stephenson]

> On 24 August 2021 at 17:23 Vincent Lefevre <vincent@vinc17.net> wrote:
> The zshmisc(1) man page says:
> 
>     ( list )
>         Execute list in a subshell.  Traps set by the trap builtin are
>         reset to their default values while executing list.
> 
> However, with "emulate sh", ignored traps should still be ignored
> in the subshell according to POSIX, and zsh 5.8 fails do conform:

I think this is straightforward.  POSIXTRAPS is clearly the option for the job.

pws

diff --git a/Src/exec.c b/Src/exec.c
index 49ff88b80..79d8064b6 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -1033,7 +1033,8 @@ entersubsh(int flags, struct entersubsh_ret *retp)
 
     if (!(flags & ESUB_KEEPTRAP))
 	for (sig = 0; sig < SIGCOUNT; sig++)
-	    if (!(sigtrapped[sig] & ZSIG_FUNC))
+	    if (!(sigtrapped[sig] & ZSIG_FUNC) &&
+		!(isset(POSIXTRAPS) && (sigtrapped[sig] & ZSIG_IGNORED)))
 		unsettrap(sig);
     monitor = isset(MONITOR);
     job_control_ok = monitor && (flags & ESUB_JOB_CONTROL) && isset(POSIXJOBS);

Re: [BUG] ignored trap and subshell

[Peter Stephenson]

> On 25 August 2021 at 11:10 Peter Stephenson <p.w.stephenson@ntlworld.com> wrote:
> > On 24 August 2021 at 17:23 Vincent Lefevre <vincent@vinc17.net> wrote:
> > The zshmisc(1) man page says:
> > 
> >     ( list )
> >         Execute list in a subshell.  Traps set by the trap builtin are
> >         reset to their default values while executing list.
> > 
> > However, with "emulate sh", ignored traps should still be ignored
> > in the subshell according to POSIX, and zsh 5.8 fails do conform:
> 
> I think this is straightforward.  POSIXTRAPS is clearly the option for the job.

And some documentation; the place Vincent mentioned looks like the obvious one
(we have at least one piece of evidence it gets read...)

diff --git a/Doc/Zsh/grammar.yo b/Doc/Zsh/grammar.yo
index 2eb2018d2..f8f4ada86 100644
--- a/Doc/Zsh/grammar.yo
+++ b/Doc/Zsh/grammar.yo
@@ -288,7 +288,9 @@ for each selection until a break or end-of-file is encountered.
 cindex(subshell)
 item(tt(LPAR()) var(list) tt(RPAR()))(
 Execute var(list) in a subshell.  Traps set by the tt(trap) builtin
-are reset to their default values while executing var(list).
+are reset to their default values while executing var(list); an
+exception is that ignored signals will continue to be ignored
+if the option tt(POSIXTRAPS) is set.
 )
 item(tt({) var(list) tt(}))(
 Execute var(list).
diff --git a/Src/exec.c b/Src/exec.c
index 49ff88b80..79d8064b6 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -1033,7 +1033,8 @@ entersubsh(int flags, struct entersubsh_ret *retp)
 
     if (!(flags & ESUB_KEEPTRAP))
 	for (sig = 0; sig < SIGCOUNT; sig++)
-	    if (!(sigtrapped[sig] & ZSIG_FUNC))
+	    if (!(sigtrapped[sig] & ZSIG_FUNC) &&
+		!(isset(POSIXTRAPS) && (sigtrapped[sig] & ZSIG_IGNORED)))
 		unsettrap(sig);
     monitor = isset(MONITOR);
     job_control_ok = monitor && (flags & ESUB_JOB_CONTROL) && isset(POSIXJOBS);

Re: [BUG] ignored trap and subshell

[Bart Schaefer]

On Wed, Aug 25, 2021 at 3:48 AM Peter Stephenson
<p.w.stephenson@ntlworld.com> wrote:
>
> And some documentation; the place Vincent mentioned looks like the obvious one
> (we have at least one piece of evidence it gets read...)

A note under the description of POSIX_TRAPS itself would not be amiss.