Re: [RFC/PATCH 1/1] format-patch: add an option to record base tree info

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 23, 2016, 06:54 UTC
Message-ID: <xmqqio1f3oi9.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20160223014741.GA21025@wfg-t540p.sh.intel.com>

Fengguang Wu <fengguang.wu@intel.com> writes:

Show 22 quoted lines

> Hi Junio,
>
> On Sun, Feb 21, 2016 at 08:19:56PM -0800, Junio C Hamano wrote:
>> Xiaolong Ye <xiaolong.ye@intel.com> writes:
>> 
>> > It would be helpful for maintainers or reviewers to know the base tree
>> > info of the patches created by git format-patch. Teach git format-patch
>> > a --base-tree-info option to record these info.
>> >
>> > Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>
>> > ---
>> 
>> I have a mixed feeling about this one, primarily because this was
>> already tried quite early in the life of "format-patch" command.
>> 
>>     http://thread.gmane.org/gmane.comp.version-control.git/9694/focus=9757
>> 
>> Only the name is different (it was called "applies-to" and named a
>> tree object).
>
> Either commit or tree object will work for us. We can use it in
> v2 if you prefer tree object.

Sorry, I think you misunderstood. By only the name is different, I didn't mean to say that the tree object name should be shown as the old proposal did. What I meant but didn't explicitly say, as I thought it was sufficient to point at an old discussion thread, was that this was already tried and rejected. This round uses different name but does essentially the same thing as the old proposal, and I do not think I heard anything new that supports this patch against earlier rejection by Linus. That is what gave me a mixed feeling.

Show 10 quoted lines

>> Is it your goal to insist on one exact commit the patch is applied
>> to?
>
> Right. Our goal is fully automated patch testing, where the base tree
> info is required for *reliably* avoid reporting false positives.
>
> A clean git-apply does not guarantee the resulted code is logically
> consistent and hence testable by 3rd party. For a 3rd party tester to
> provide useful and trustable test reports, he must apply the patch to
> exactly the same base as the patch submitter.

The patch submitter (or you as a third party tester) is not in the position to dictate the integrator to apply the patch to one specific commit and use it from there. The integrator would pick an appropriate base that would be different from the commit where the patch was taken from, apply it there, and merge the result to the tip of the mainline, or apply the patch directly to the tip of the mainline. Even if the integrator picked the commit the patch was taken from, the result would not be used alone without any other changes, i.e. before getting merged into the integration branch.

So in that sense, any test that is done by the patch submitter and the third party tester would not be what will be released to the wild *anyway*. The resulting code will be exercised in a context that *is* different from the context the original author had.

I can see that recording the exact commit object name allows you to claim that you identified the exact commit to apply the patch, and that you tested the exact tree contents. It however is unclear what the value of such a claim would be to the project or to the integrator.

So I dunno.