forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
96 lines
4.7 KiB
96 lines
4.7 KiB
.. SPDX-License-Identifier: GPL-2.0 |
|
|
|
===================================== |
|
Handling messy pull-request diffstats |
|
===================================== |
|
|
|
Subsystem maintainers routinely use ``git request-pull`` as part of the |
|
process of sending work upstream. Normally, the result includes a nice |
|
diffstat that shows which files will be touched and how much of each will |
|
be changed. Occasionally, though, a repository with a relatively |
|
complicated development history will yield a massive diffstat containing a |
|
great deal of unrelated work. The result looks ugly and obscures what the |
|
pull request is actually doing. This document describes what is happening |
|
and how to fix things up; it is derived from The Wisdom of Linus Torvalds, |
|
found in Linus1_ and Linus2_. |
|
|
|
.. _Linus1: https://lore.kernel.org/lkml/CAHk-=wg3wXH2JNxkQi+eLZkpuxqV+wPiHhw_Jf7ViH33Sw7PHA@mail.gmail.com/ |
|
.. _Linus2: https://lore.kernel.org/lkml/CAHk-=wgXbSa8yq8Dht8at+gxb_idnJ7X5qWZQWRBN4_CUPr=eQ@mail.gmail.com/ |
|
|
|
A Git development history proceeds as a series of commits. In a simplified |
|
manner, mainline kernel development looks like this:: |
|
|
|
... vM --- vN-rc1 --- vN-rc2 --- vN-rc3 --- ... --- vN-rc7 --- vN |
|
|
|
If one wants to see what has changed between two points, a command like |
|
this will do the job:: |
|
|
|
$ git diff --stat --summary vN-rc2..vN-rc3 |
|
|
|
Here, there are two clear points in the history; Git will essentially |
|
"subtract" the beginning point from the end point and display the resulting |
|
differences. The requested operation is unambiguous and easy enough to |
|
understand. |
|
|
|
When a subsystem maintainer creates a branch and commits changes to it, the |
|
result in the simplest case is a history that looks like:: |
|
|
|
... vM --- vN-rc1 --- vN-rc2 --- vN-rc3 --- ... --- vN-rc7 --- vN |
|
| |
|
+-- c1 --- c2 --- ... --- cN |
|
|
|
If that maintainer now uses ``git diff`` to see what has changed between |
|
the mainline branch (let's call it "linus") and cN, there are still two |
|
clear endpoints, and the result is as expected. So a pull request |
|
generated with ``git request-pull`` will also be as expected. But now |
|
consider a slightly more complex development history:: |
|
|
|
... vM --- vN-rc1 --- vN-rc2 --- vN-rc3 --- ... --- vN-rc7 --- vN |
|
| | |
|
| +-- c1 --- c2 --- ... --- cN |
|
| / |
|
+-- x1 --- x2 --- x3 |
|
|
|
Our maintainer has created one branch at vN-rc1 and another at vN-rc2; the |
|
two were then subsequently merged into c2. Now a pull request generated |
|
for cN may end up being messy indeed, and developers often end up wondering |
|
why. |
|
|
|
What is happening here is that there are no longer two clear end points for |
|
the ``git diff`` operation to use. The development culminating in cN |
|
started in two different places; to generate the diffstat, ``git diff`` |
|
ends up having pick one of them and hoping for the best. If the diffstat |
|
starts at vN-rc1, it may end up including all of the changes between there |
|
and the second origin end point (vN-rc2), which is certainly not what our |
|
maintainer had in mind. With all of that extra junk in the diffstat, it |
|
may be impossible to tell what actually happened in the changes leading up |
|
to cN. |
|
|
|
Maintainers often try to resolve this problem by, for example, rebasing the |
|
branch or performing another merge with the linus branch, then recreating |
|
the pull request. This approach tends not to lead to joy at the receiving |
|
end of that pull request; rebasing and/or merging just before pushing |
|
upstream is a well-known way to get a grumpy response. |
|
|
|
So what is to be done? The best response when confronted with this |
|
situation is to indeed to do a merge with the branch you intend your work |
|
to be pulled into, but to do it privately, as if it were the source of |
|
shame. Create a new, throwaway branch and do the merge there:: |
|
|
|
... vM --- vN-rc1 --- vN-rc2 --- vN-rc3 --- ... --- vN-rc7 --- vN |
|
| | | |
|
| +-- c1 --- c2 --- ... --- cN | |
|
| / | | |
|
+-- x1 --- x2 --- x3 +------------+-- TEMP |
|
|
|
The merge operation resolves all of the complications resulting from the |
|
multiple beginning points, yielding a coherent result that contains only |
|
the differences from the mainline branch. Now it will be possible to |
|
generate a diffstat with the desired information:: |
|
|
|
$ git diff -C --stat --summary linus..TEMP |
|
|
|
Save the output from this command, then simply delete the TEMP branch; |
|
definitely do not expose it to the outside world. Take the saved diffstat |
|
output and edit it into the messy pull request, yielding a result that |
|
shows what is really going on. That request can then be sent upstream.
|
|
|