Re: bin/48843: sh(1): break/continue/return broken inside dot commands

[David Holland <dholland-tech%netbsd.org@localhost>]

The following reply was made to PR bin/48843; it has been noted by GNATS.

From: David Holland <dholland-tech%netbsd.org@localhost>
To: Richard Hansen <rhansen%bbn.com@localhost>
Cc: jarmo.jaakkola%roskakori.fi@localhost, gnats-bugs%NetBSD.org@localhost,
        tech-userlevel%NetBSD.org@localhost
Subject: Re: bin/48843: sh(1): break/continue/return broken inside dot
 commands
Date: Sat, 31 May 2014 23:51:35 +0000

 On Sat, May 31, 2014 at 05:14:26PM -0400, Richard Hansen wrote:
  > > Whether break and continue should work from the sourced
  > > file might be debatable.  Because the dot command says "in the current
  > > environment", I'd say yes.
  > 
  > Not necessarily.  POSIX does not define "enclosing loop", so it could be
  > interpreted as syntactic enclosure (a break/continue command must be a
  > command in the compound list associated with the loop for the loop to
  > qualify as enclosing the command) or logical enclosure as experienced
  > during execution.  I can see pros and cons to either behavior.
 
 Offhand, I would say that continues and breaks should be statically
 scoped; dynamic scoping is almost always a mistake. So you certainly
 shouldn't be able to break from a loop by calling a function that
 contains a break outside a loop. (Although netbsd's sh, bash, and zsh
 all seem to allow this, I would call it a bug. ksh rejects it.)
 
 How this applies to a sourced file isn't so clear though, at least
 offhand, as the point of sourcing a file is to read and evaluate it
 within the current context. My inclination would be that sourcing a
 file is not the same as calling a function; however, I'm far from an
 expert on sh.
 
 It seems that the behavior of sourcing with respect to $0 and $@
 varies among implementations, which doesn't make me happy.
 
  > I will bring this up during the next Austin Group teleconference.  We
  > should be able to get some improved wording in before POSIX Issue 7 TC2
  > is published (even if that wording is simply "unspecified" or
  > "implementation defined").  Any input from the NetBSD community would be
  > appreciated.
  > 
  > The intended behavior of break/continue outside of a loop is also
  > unclear.  I'll bring that up as well.
 
 netbsd's sh seems to accept it silently; ksh, bash, and zsh all reject
 it. I would consider our sh broken.
 
  > > Because I read the standard to mean that break and continue should have
  > > an effect outside the sourced file, that's how I implemented it.  For what
  > > it's worth, this also seems to be what bash does.
  > 
  > The behavior of existing implementations will strongly influence the
  > direction the Austin Group takes when revising the text.  With that
  > said, what behavior would you like POSIX to specify?
 
 With stuff like this, I'd rather fix our implementation (or have it be
 noncompliant until fixed) than standardize unprincipled behavior. FWIW.
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost