Re: t5570 trap use in start/stop_git_daemon

From: Jeff King <peff@peff.net>
Date: Feb 13, 2015, 08:03 UTC
Message-ID: <20150213080359.GC26775@peff.net>
In-Reply-To: <20150213074403.GB26775@peff.net>

On Fri, Feb 13, 2015 at 02:44:03AM -0500, Jeff King wrote:

Show 12 quoted lines

> On Thu, Feb 12, 2015 at 03:31:12PM -0500, Randall S. Becker wrote:
> 
> > On the NonStop port, we found that trap was causing an issue with test
> > success for t5570. When start_git_daemon completes, the shell (ksh,bash) on
> > this platform is sending a signal 0 that is being caught and acted on by the
> > trap command within the start_git_daemon and stop_git_daemon functions. I am
> > taking this up with the operating system group,
> 
> Yeah, that seems wrong. If it were a subshell, even, I could see some
> argument for it, but it seems odd to trap 0 when a function returns
> (bash does have a RETURN trap, which AFAIK is bash-specific, but it
> should not trigger a 0-trap).

Hmm, today I learned something new about ksh. Apparently when you use the "function" keyword to define a function like:

  function foo {
    trap 'echo trapped' EXIT
  }
  echo before
  foo
  echo after

then the trap runs when the function exits! If you declare the same function as:

  foo() {
    trap 'echo trapped' EXIT
  }

it behaves differently. POSIX shell does not have the function keyword, of course, and we are not using it here. Bash _does_ have the function keyword, but seems to behave POSIX-y even when it is present. I.e., running the first script:

  $ ksh foo.sh
  before
  trapped
  after

  $ bash foo.sh
  before
  after
  trapped

  $ dash foo.sh
  foo.sh: 3: foo.sh: function: not found
  foo.sh: 5: foo.sh: Syntax error: "}" unexpected

Switching to the second form, all three produce:

  before
  after
  trapped

I don't know if that is all helpful to your bug-tracking or analysis, but for whatever reason it looks like your ksh is using localized traps for both forms of function. But as far as I know, bash has never behaved that way (I just grepped its CHANGES file for mentions of trap and found nothing likely).

-Peff