Re: bug: git-diff silently fails when run outside of a repository (v1.5.4.2)

[Junio C Hamano <gitster@pobox.com>]

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

>> > Even so, this seems like a bug.  If I do this:
>> >
>> >     $ cd /
>> >     $ git-diff
>> >
>> > there is no error message and no error status.  A diagnostic would be
>> > very helpful.
>> 
>> Ah, that indeed is not very helpful.
>> 
>> Unfortunately, every time I look at this hack, I seem to find an unrelated
>> bug in it.  Here is today's.
>> 
>> 	$ for i in 1 2 3; do >/var/tmp/$i; done
>>         $ cd /
>>         $ git diff /var/tmp/1
>>         Segmentation Fault
>> 
>> When nongit is true, we know the user has to be asking --no-index diff, so
>> perhaps we can fix it by doing something like this?
>> 
>> diff --git a/diff-lib.c b/diff-lib.c
>> index 069e450..cfd629d 100644
>> --- a/diff-lib.c
>> +++ b/diff-lib.c
>> @@ -264,6 +264,9 @@ int setup_diff_no_index(struct rev_info *revs,
>>  			DIFF_OPT_SET(&revs->diffopt, EXIT_WITH_STATUS);
>>  			break;
>>  		}
>> +	if (nongit && argc != i + 2)
>> +		die("git diff [--no-index] takes two paths");
>> +
>>  	if (argc != i + 2 || (!is_outside_repo(argv[i + 1], nongit, prefix) &&
>>  				!is_outside_repo(argv[i], nongit, prefix)))
>>  		return -1;
>
> That looks to me as if the second if() should have triggered, and the 
> caller of setup_diff_no_index() should have errored out.

I think the above three-liner fix is something we should have done when we
added --no-index codepath.  Before the --no-index hack was introduced, we
did not even got this far to the place the caller of this function is, if
we are outside a repository.  By returning -1 from here instead of dying,
this code is driving the codepath that has always expected to already be
in a repository into a nonrepository, causing them to segfault because
there is no git-dir or work-tree set up done yet as they expect.