suspend (^Z) behavior while a function is running is unclear

[Vincent Lefevre <vincent@vinc17.net>]

I've reported the following problem on

  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=660630

The suspend (^Z) behavior while a function is running is unclear.
The documentation (man pages) should describe the behavior. There
may be a bug in zsh, as some other shells don't behave in the same
way.

Consider:

foo() { emacs "$@"; d=`date`; echo "$d"; }

and the following test under X (so that Emacs uses its own window,
or you can try with another X application):

1. Run foo.
2. Type ^Z in the terminal.
3. Type: fg [Return].
4. Quit Emacs.
5. Type: echo "$d" [Return].

With zsh, the whole function is suspended. The effect is that zsh is
forked (this is not documented, though can be guessed), thus $d will
not be set in the main shell (Step 5: nothing is displayed).

With bash, dash, mksh and pdksh, only the emacs process is suspended.
With ksh93, the ^Z is ignored until Emacs is quit, then the function
is suspended, with the same effects as in zsh. With posh, the whole
shell is suspended.

Versions of the packages:
  bash 4.2-1
  dash 0.5.7-2
  ksh 93u-1
  mksh 40.4-3
  pdksh 5.2.14-26
  posh 0.10.1
  zsh 4.3.15-1
  zsh-beta 4.3.15-dev-0+20120108-1

BTW, concerning zsh, if the behavior is regarded as correct, a fork
is still done even when the suspended command is the last one in the
function, e.g.

  foo() { emacs "$@"; }

Is the fork really necessary?

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)