Re: Bring together merge and rebase

> On Mon, Dec 25, 2017 at 05:47:55PM -0800, Jacob Keller wrote:
>> On Mon, Dec 25, 2017 at 5:16 PM, Carl Baldwin <carl@ecbaldwin.net> wrote:
>> > Anyway, now I am compelled to use github which is also a fine tool and I
>> > appreciate all of the work that has gone into it. About 80% of the time,
>> > I rebase and force push to my branch to update a pull request. I've come
>> > to like the end product of the rebase workflow. However, github doesn't
>> > excel at this approach. For one, it doesn't preserve older revisions
>> > which were already reviewed which makes it is difficult for reviewers to
>> > pick up where they left off the last time. If it preserved them, as
>> > gerrit does, the reviewer can compare a new revision with the most
>> > recent older revision they reviewed to see just what has been addressed
>> > since then.
>>
>> A bit of a tangent here, but a thought I didn't wanna lose: In the
>> general case where a patch was rebased and the original parent pointer
>> was changed, it is actually quite hard to show a diff of what changed
>> between versions.
>>
>> The best I've found is to do something like a 4-way --cc merge diff,
>> which mostly works, but has a few awkward cases, and ends up usually
>> showing double ++ and -- notation.
>>
>> Just something I've thought about a fair bit, trying to come up with
>> some good way to show "what changed between A1 and A2, but ignore all
>> changes between parent P1 and P2 which you don't care that much about
>> in this context.
>
> I ran into this all the time with gerrit. I wrote a script that you'd
> run on a working copy (with no local changes). I'd fetch and checkout
> the latest patchset that I want to review(say, for example, its patchset
> 5) from gerrit. Then, say I wanted to compare it with patch set 3 which
> has a different parent. I'd run this from the top level of my working
> copy.
>
>     compare-to-previous-patchset 3
>
> It would fetch patch set 3 from gerrit, rebase it to the same parent as
> the current patch set on a detached HEAD and then git diff it with the
> current patch set. If there were conflicts, it would just commit the
> conflict markers to the commit. There is no attempt to resolve the
> conflicts. The script was crude but it helped me out many times and it
> was nice to be able to review how conflicts were resolved when those
> came up.
>
> Carl
>

> PS In case you're curious, here's my script...
>
> #!/bin/bash
>
> remote=gerrit
> previous_patchset=$1; shift
>
> # Assumes we're sitting on the latest patch set.
> new_patch_set_id=$(git rev-parse HEAD)
>
> branch=$(git branch | awk '/^\*/ {print$2}')
> [ "$branch" = "(no" ] && branch=
>
> # set user, host, port, and project from git config
> eval $(echo "$(git config remote.$remote.url)" |
>        sed 's,ssh://\(.*\)@\(.*\):\([[:digit:]]*\)/\(.*\).git,user=\1 host=\2 p<
>
> gerrit() {
>     ssh $user@$host -p $port gerrit ${1+"$@"}
> }
>
> # Grabs a bunch of information from gerrit about the current patch
> eval $(gerrit query --current-patch-set $new_patch_set_id |
>     awk '
>         BEGIN {mode="main"}
>         / currentPatchSet:/ { mode="currentPatchSet" }
>         / ref:/ { printf "new_patch_ref=%s\n", $2 }
>         / number:/ {
>             if (mode=="main") {
>                 printf "review_num=%s\n", $2
>             }
>             if (mode=="currentPatchSet") {
>                 printf "new_patchset=%s\n", $2
>             }
>         }
>     ')
>
> # Fetch the old patch set
> old_patch_ref=${new_patch_ref%$new_patchset}$previous_patchset
> git fetch $remote $old_patch_ref && git checkout FETCH_HEAD
>
> # Rebase the old patch set to the parent of the new patch set.
> if ! git rebase HEAD^ --onto ${new_patch_set_id}^
> then
>     git diff --name-only --diff-filter=U -z | xargs -0 git add
>     git rebase --continue
> fi
>
> previous_patchset_rebased=$(git rev-parse HEAD)
>
> # Go back to the new patch set and diff it against the rebased old one.
> if [ "$branch" ]
> then
>     git checkout $branch
> else
>     git checkout $new_patch_set_id
> fi
> git diff $previous_patchset_rebased