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

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

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

> 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.

>> 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.