[BUG] dash doesn't report syntax error when it should on stray "fi"

[BUG] dash doesn't report syntax error when it should on stray "fi"

[Stefano Lattarini]

How to reproduce:

  $ dash -c ':; fi'; echo stat = $?
  stat = 0

Behaviour of other shells:

  $ bash-4.1 -c ':; fi'; echo stat = $?  # Bash 4.1.5
  bash-4.1: -c: line 0: syntax error near unexpected token `fi'
  bash-4.1: -c: line 0: `:; fi'
  stat = 1

  $ bash-3.2 -c ':; fi'; echo stat = $? # Bash 3.2.0
  bash-3.2: -c: line 0: syntax error near unexpected token `fi'
  bash-3.2: -c: line 0: `:; fi'
  stat = 2

  $ ksh -c ':; fi'; echo stat = $? # AT&T Ksh
  ksh: syntax error at line 1: `fi' unexpected
  stat = 3

  $ pdksh -c ':; fi'; echo stat = $? # Public Domain Ksh, version 5.2.14
  pdksh: syntax error: `fi' unexpected
  stat = 1

  $ zsh -c ':; fi'; echo stat = $?  # Zsh 4.3.12
  zsh:1: parse error near `fi'
  stat = 1


Version information:

  $ dpkg -l dash
  ii   dash   0.5.5.1-7.4   POSIX-compliant shell

Regards,
  Stefano

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Jonathan Nieder]

Hi Stefano,

Stefano Lattarini wrote:

> How to reproduce:
>
>   $ dash -c ':; fi'; echo stat = $?
>   stat = 0

Since this doesn't affect conforming scripts, I suspect it falls
squarely within the "patches welcome as long as they don't make dash
bigger" category.

Thanks for finding it.

Sincerely,
Jonathan

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Stefano Lattarini]

Hi Jonathan, thanks for the quick reply.

On 04/23/2012 07:03 PM, Jonathan Nieder wrote:
> Hi Stefano,
> 
> Stefano Lattarini wrote:
> 
>> How to reproduce:
>>
>>   $ dash -c ':; fi'; echo stat = $?
>>   stat = 0
> 
> Since this doesn't affect conforming scripts,
>
True, it it makes "dash -n" less useful (not that I deeply care, just pointing
it out).

> I suspect it falls squarely within the "patches welcome as long as they
> don't make dash bigger" category.
> 
> Thanks for finding it.
> 
> Sincerely,
> Jonathan

Thanks,
  Stefano

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Chet Ramey]

On 4/23/12 1:03 PM, Jonathan Nieder wrote:
> Hi Stefano,
> 
> Stefano Lattarini wrote:
> 
>> How to reproduce:
>>
>>   $ dash -c ':; fi'; echo stat = $?
>>   stat = 0
> 
> Since this doesn't affect conforming scripts, I suspect it falls
> squarely within the "patches welcome as long as they don't make dash
> bigger" category.

What are `conforming scripts'?  Scripts without syntax errors?

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Jonathan Nieder]

Chet Ramey wrote:

> What are `conforming scripts'?  Scripts without syntax errors?

I meant "conforming POSIX applications".

A patch for this might even be welcome if it makes dash bigger, if
that's what you're wondering.

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Chet Ramey]

On 4/23/12 3:44 PM, Jonathan Nieder wrote:
> Chet Ramey wrote:
> 
>> What are `conforming scripts'?  Scripts without syntax errors?
> 
> I meant "conforming POSIX applications".
> 
> A patch for this might even be welcome if it makes dash bigger, if
> that's what you're wondering.

The way I read 2.10.2, Posix requires that the "fi" resolve to the
reserved word `fi' in this case, since it's in a position where a
command name is expected (Rule 1, [Command Name]).  I would think that
would make it a syntax error in any application, conforming or not.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Stefano Lattarini]

Hi Jonathan, Chet.

On 04/23/2012 09:44 PM, Jonathan Nieder wrote:
> Chet Ramey wrote:
> 
>> What are `conforming scripts'?  Scripts without syntax errors?
> 
> I meant "conforming POSIX applications".
> 
> A patch for this might even be welcome if it makes dash bigger, if
> that's what you're wondering.
>
I have no patch, but a little more information that might help anyone who
volunteers to write one:

  $ nl=$'\n'

  $ dash -c ":$nl fi" && echo NOERR
  dash: Syntax error: "fi" unexpected

  $ dash -c ":;$nl fi" && echo NOERR
  dash: Syntax error: "fi" unexpected

  $ dash -c ":&$nl fi" && echo NOERR
  dash: Syntax error: "fi" unexpected

  $ dash -c ": && fi" && echo NOERR
  dash: Syntax error: "fi" unexpected

The problem seems to only be present when a stray "fi" comes after a
'&' or ';' -- see:

  $ dash -c ":; fi" && echo NOERR
  NOERR

  dash -c ":& fi" && echo NOERR
  NOERR


The same goes for other loops/conditionals terminators:

  $ dash -c ":; done" && echo NOERR
  NOERR

  $ dash -c ":; esac" && echo NOERR
  NOERR

  $ dash -c ":& elif" && echo NOERR
  NOERR

HTH,
  Stefano

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Jonathan Nieder]

Chet Ramey wrote:

> The way I read 2.10.2, Posix requires that the "fi" resolve to the
> reserved word `fi' in this case, since it's in a position where a
> command name is expected (Rule 1, [Command Name]).  I would think that
> would make it a syntax error in any application, conforming or not.

Yes, I think you're right.

For some reason I thought that using reserved words in ways not
permitted by the grammar produced undefined behavior, to support
shells with extensions like the arithmetic "for".  But now that I read
more closely, it looks like "function", "[[", "]]", and "select"
produce unspecified behavior but everything else is pretty well
specified.  Thanks for clarifying.

Re: [BUG] dash doesn't report syntax error when it should on stray "fi"

[Jilles Tjoelker]

On Mon, Apr 23, 2012 at 02:54:58PM -0500, Jonathan Nieder wrote:
> Chet Ramey wrote:

> > The way I read 2.10.2, Posix requires that the "fi" resolve to the
> > reserved word `fi' in this case, since it's in a position where a
> > command name is expected (Rule 1, [Command Name]).  I would think that
> > would make it a syntax error in any application, conforming or not.

> Yes, I think you're right.

> For some reason I thought that using reserved words in ways not
> permitted by the grammar produced undefined behavior, to support
> shells with extensions like the arithmetic "for".  But now that I read
> more closely, it looks like "function", "[[", "]]", and "select"
> produce unspecified behavior but everything else is pretty well
> specified.  Thanks for clarifying.

In what way does a lone "fi" differ from constructions like the below,
which do not match the POSIX grammar but are accepted by some subset of
shells that attempt to comply to POSIX:

case x in (esac) ;; esac

for i; do echo "$i"; done

for i;
do echo "$i"; done

for i { echo "$i"; }

for ((i = 0; i < 10; i += 1)) do echo "$i"; done

f() :

The only difference seems to be that the lone "fi" is somehow "wrong"
while the above are not "wrong". That's too vague for a specification.

Unfortunately, the XCU volume is very thin on constraints (as found, for
example, in the C standard). Many ways to do things "wrong" are instead
left open for implementation extensions. In practice, many such
extensions exist.

That said, rejecting the lone "fi" is still a quality of implementation
issue, particularly because dash's current behaviour is poorly defined.
I fixed it in FreeBSD a while ago (9.0 has the fix).

In making this change, a testsuite is very useful to guard against bugs
and to ensure no cases are missed, but latent bugs in shell scripts may
still cause annoyance. If there is an error in a command substitution
that is normally not executed, most shells (except ash derivatives) will
not notice this.

For example, FreeBSD 9.0's sh is one of the few shells that detects the
error in:

if false; then `fi`; fi

-- 
Jilles Tjoelker