expand: Fix ghost fields with unquoted $@/$*

Harald van Dijk <harald@gigawatt.nl> wrote:
> On 22/03/2018 22:38, Martijn Dekker wrote:
>> Op 22-03-18 om 20:28 schreef Harald van Dijk:
>>> On 22/03/2018 03:40, Martijn Dekker wrote:
>>>> This patch fixes the bug that, given no positional parameters, unquoted
>>>> $@ and $* incorrectly generate one empty field (they should generate no
>>>> fields). Apparently that was a side effect of the above.
>>>
>>> This seems weird though. If you want to remove the recording of empty
>>> regions because they are pointless, then how does removing them fix a
>>> bug? Doesn't this show that empty regions do have an effect? Perhaps
>>> they're not supposed to have any effect, perhaps it's a specific
>>> combination of empty regions and something else that triggers some bug,
>>> and perhaps that combination can no longer occur with your patch.
>>
>> The latter is my guess, but I haven't had time to investigate it.
>
> Looking into it again:
>
> When IFS is set to an empty string, sepc is set to '\0' in varvalue().
> This then causes *quotedp to be set to true, meaning evalvar()'s quoted
> variable is turned on. quoted is then passed to recordregion() as the
> nulonly parameter.
>
> ifsp->nulonly has a bigger effect than merely selecting whether to use
> $IFS or whether to only split on null bytes: in ifsbreakup(), nulonly
> also causes string termination to be suppressed. That's correct: that
> special treatment is required to preserve empty fields in "$@"
> expansion. But it should *only* be used when $@ is quoted: ifsbreakup()
> takes nulonly from the last IFS region, even if it's empty, so having an
> additional zero-length region with nulonly enabled causes confusion.
>
> Passing quoted by value to varvalue() and not attempting to modify it
> should therefore, and in my quick testing does, also work to fix the
> original $@ bug.

You're right.  The proper fix to this is to ensure that nulonly
is not set in varvalue for $*.  It should only be set for $@ when
it's inside double quotes.

In fact there is another bug while we're playing with $@/$*.
When IFS is set to a non-whitespace character such as :, $*
outside quotes won't remove empty fields as it should.

This patch fixes both problems.

Reported-by: Martijn Dekker <martijn@inlv.org>
Suggested-by: Harald van Dijk <harald@gigawatt.nl>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

0 files changed, 0 insertions, 0 deletions