Re: [PATCH v4 2/3] diff: Let "git diff -O" read orderfile from any file, fail properly

> On Mon, Dec 16, 2013 at 4:32 PM, Junio C Hamano <gitster@pobox.com> wrote:
>> Samuel Bronson <naesten@gmail.com> writes:
>>
>>>  for i in 1 2
>>>  do
>>>       test_expect_success "orderfile using option ($i)" '
>>>       git diff -Oorder_file_$i --name-only HEAD^..HEAD >actual &&
>>>       test_cmp expect_$i actual
>>>  '
>>
>> This funny indentation in the previous step needs to be fixed, and
>> the added block below should match.
>
> Even though this results in oddly-indented --verbose output?
>
>>> +     rm -f order_fifo &&
>>> +     mkfifo order_fifo &&
>>> +     cat order_file_$i >order_fifo &
>>> +     git diff -O order_fifo --name-only HEAD^..HEAD >actual &&
>>
>> I think this part can be racy depending on which between cat and
>> "git diff" are scheduled first, no?  Try running this test under
>> load and I think you will see it deadlocked.
>>
>> Besides, the above breaks && chain; even if mkfifo breaks (hence not
>> allowing cat to run), "git diff" will go ahead and run, no?
>
> Hmm.  Well, what I really wanted to put here was a "process substitution":
>
>     git diff -O <(cat order_file_$i) --name-only HEAD^..HEAD >actual &&
>
> but I did not see this feature listed in the dash(1) manpage, so I
> assumed it wasn't allowed by POSIX.  And, having looked, I indeed
> don't see it mentioned in POSIX either.
>
> I'm not terribly surprised that I screwed up the translation to FIFOs;
> how would I really want to do it?