[llvm-dev] Git question about revert

[Fangrui Song via llvm-dev]

On 2021-01-21, David Blaikie via llvm-dev wrote:
>Definite +1 to this - please include the full history of the patches
>commit/reverts, and reasons for them. (eg: "originally committed as <hash>
>reverted due to <buildbot info (link and quote ideally, the logs get
>cleaned up so the link won't be around forever but the commit
>message/quoted errors/etc will be)> recommitted as <hash> with <describe
>the fix/pointing to particular source files/changes>, etc... " - I usually
>do that in list form:
><hash> originally committed
><hash> reverted due to...
><hash> recommitted with fix...
>...
>)

Some new contributors tend to make reverts without a justification.

https://llvm.org/docs/DeveloperPolicy.html#commit-messages actually has
a somewhat related sentence but it is probably buried in a long document.

"If the commit is a bug fix on top of another recently committed patch,
or a revert or reapply of a patch, include the git commit hash of the
prior related commit. This could be as simple as “Revert commit NNNN
because it caused PR#”."


There are some other undocumented good practices, e.g.

* If the patch may take some time to reland or miss something more than
   simple test tweaks, consider reopening the differential and (if
   requires further review) requesting for changes.
* `git cherry-pick`. Make sure `Differential Revision: ` is in the
   reland commit so that it is connected to the original differential.

>On Thu, Jan 21, 2021 at 12:11 AM James Henderson via llvm-dev <
>llvm-dev at lists.llvm.org> wrote:
>
>> One other thing I find useful when relanding a patch after fixing it is to
>> include in the new commit message the reason for the breakage/how the new
>> patch fixes it.
>>
>> James
>>
>> On Wed, 20 Jan 2021 at 21:23, Mehdi AMINI via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>>
>>>
>>> On Wed, Jan 20, 2021 at 10:39 AM Paul C. Anagnostopoulos via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> This morning I pushed a commit that killed the build, so I reverted it
>>>> and pushed the new commit to fix the build. Then I did another revert to
>>>> get my changes back so I can work on them some more.
>>>>
>>>> Is it legitimate to use that second revert commit, which was never
>>>> pushed, to do the additional work, changing the title to something
>>>> reasonable? If not, could you explain what I ought to do?
>>>>
>>>
>>> That works, in general I tend to `git cherry-pick <original commit>`
>>> instead, because it brings back the original commit description with it :)
>>> (and possible link to the phabricator revision).
>>> I'll still edit the message (git commit --amend) to add that this is a
>>> reland after fixes.
>>>
>>> --
>>> Mehdi
>>>
>>>>
>>>> _______________________________________________
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