When someone makes a PR, they may be asked to rebase their feature branch onto
main to resolve conflicts. It may be useful to quickly see what changed during
the rebase, that is how the new version of PR is different to the old one.
If the PR branch has not been reparented, you may get away with `git diff`.
But if it has, `git diff` may contain a lot of changes from upstream. Instead,
`git range-diff` can be used.
The problem with this is that in this case `git range-diff` can show chunks
with changes that have nothing to do with changes in the PR. Consider this
repository (commands are runnable):
git init
git branch -m main
echo -e "a\nb\nc\nd\ne\n1\n2\n3\nf" > file
git add file
git commit -am "a b c d e f"
git checkout -b foo
echo -e "a\nb\nc\nd\ne\n1\n2\n3\nfoo" > file
git commit -am "f -> foo"
git checkout main
git checkout -b cat
echo -e "a\nb\ncat\nd\ne\n1\n2\n3\nf" > file
git commit -am "c -> cat"
We got a few letters of alphabet on separate lines on main, and in branch
foo `f` is changed to `foo`, and in branch cat `c` is changed to `cat`.
$ git log --all --graph --pretty=oneline
* 90e873e3 (HEAD -> cat) c -> cat
| * 3d8c1baf (foo) f -> foo
|/
* 4d2337dd (main) a b c d e f
Now, still on cat, let's combine the two changes.
$ git rebase foo
Successfully rebased and updated refs/heads/cat
$ git log --all --graph --pretty=oneline
* 98e554a0 (HEAD -> cat) c -> cat
* 3d8c1baf (foo) f -> foo
* 4d2337dd (main) a b c d e f
Now, `git rebase foo` worked automatically, so *the change* of the last commit
on `cat` is the same as it was without rebase, which is changing `c` to `cat`.
But if we run `git range-diff`, we will see this:
$ git range-diff 90e873e3...cat
-: ------- > 1: 3d8c1ba f -> foo
1: 90e873e ! 2: 98e554a c -> cat
@@ file
+cat
d
e
- f
+ foo
It seems that this chunk is included for the sole reason that the change from
`foo` is sort of close. If we try the same code, but put the lines `c` and `f`
further apart, for example by replacing `e\n` with `e\n1\n2\n3\n` in the
commands above, the output would be, as expected,
$ git range-diff f1e0a6cc3...cat
-: ------- > 1: 4db06be f -> foo
1: f1e0a6c = 2: cc56db7 c -> cat
I suggest not showing uninteresting chunks like that, or perhaps having a
command line option that controls how close together the changes must be in
order to be included in the output.
