Re: Git bisect run should check for the existence of the script

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 17, 2020, 19:17 UTC
Message-ID: <xmqqeepadk8q.fsf@gitster.c.googlers.com>
In-Reply-To: <8c683b56-d17a-78ce-67bb-477e5b307df9@abou-samra.fr>

Jean Abou Samra <jean@abou-samra.fr> writes:

Show 18 quoted lines

> Le 15/07/2020 à 16:55, Junio C Hamano a écrit :
>> Jean Abou Samra <jean@abou-samra.fr> writes:
>>
>>> $ git bisect run ./non-existent.sh
>>> running ./non-existent.sh
>>> /usr/lib/git-core/git-bisect: 247: ./non-existent.sh: not found
> ...
>> On the other hand, the "./non-existent.sh" script could be part of
>> the tracked contents (i.e. some revisions have it and the working
>> tree has it when they get checked out, some revisions don't and the
>> working tree does not have it), and the user is trying to find the
>> first revision that stopped having a working script in its tree.  In
>> such a case, the script that does not exist and the script that fails
>> need to be treated the same way by "git bisect run" as failures.
>>
>> So... I dunno.
>
> Perhapsa --not-found-as-failure option could help?

Do you mean a new option must be passed if the end-user expects the script to always exist across revisions, or the script is not tracked to begin with? It feels somewhat backwards and the effort by the end-user to always type the option is better spent to make sure there is no typo on the command line.

Besides, we need to take into account that "bisect run" takes an arbitrary shell snippet, e.g. the user may try to switch between two scripts, test-1 and test-2, based on some condition, and wrote this:

  $ git bisect run "if some-condition; then ./test-1; else ./test-3; fi"

but made a typo in the name of test-2. It would be noticed after attempting to run the "if ... fi" as a scriptlet by the returned status from it being 127 (command not found), which is not treated any specially by "git bisect run". So a typo in the script name in the above example cannot be distinguished from this error where the user wanted to run test-1 under some condition, but wanted to declare that the revision is bad if that condition did not hold, i.e.

  $ git bisect run "if some-condition; then ./test-1; else (exit 127); fi"

Even if we somehow could tell these two apart, we cannot pick the first scriptlet apart and guess which substring in it were meant as a filename with a typo.

It may be possible to forbid the general use of exit code 127 and instead reserve it to signal "we know that the test script is so broken (this includes the case where it does not even exist) that using it with 'bisect run' is meaningless; please stop immediately." and nothing else, just like exit code 125 is reserved for "this revision is not testable and cannot say good or bad", but making such a change retroactively is not to be done very lightly.

So, again, I dunno.

 git-bisect.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/git-bisect.sh b/git-bisect.sh
index 7a8f796251..5c03bf8533 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -122,7 +122,7 @@ bisect_run () {
 		res=$?
 
 		# Check for really bad run error.
-		if [ $res -lt 0 -o $res -ge 128 ]
+		if [ $res -lt 0 -o $res -ge 128 -o $res -eq 127 ]
 		then
 			eval_gettextln "bisect run failed:
 exit code \$res from '\$command' is < 0 or >= 128" >&2