Sadly no one cares about this issue... This bug is especially obvious
if we simply run `git subtree push` after a `git subtree add --squash`:
If master is at commit D, which is generated by
`git subtree add --squash -P sub Y`:
A---B---C---D master
/
Y'
X---Y sub
After running `git subtree push -P sub . sub`, we get:
A---B---C---D' sub (after push, actual)
/
X---Y
While the sub branch should not change at all!
This bug, seemingly introduced by 933cfeb90b5d03b4096db6d60494a6eedea25d03
critically makes --squash approach for `git subtree` almost unusable.
Added related developers to CC list for better notice.
>
> Say we have a repository with "master" and "sub" branches like below:
>
> A---B---C---D---E---F master
> /
> X---Y
>
> X---Y sub
>
> where commits A and B include changes in subdirectory "sub", commit C
> removes subdirectory "sub", commit D is generated by "git subtree add
> -P sub Y", and commits E and F also include changes in subdirectory
> "sub".
>
> We'd get this if we run "git subtree push -P sub . sub" on master at F:
>
> X---Y---E'--F' sub (after push)
>
> On the other hand, if we have simliar trees except that commit D is
> generated by "git subtree add --squash -P sub Y":
>
> A---B---C---D---E---F master
> /
> Y'
>
> X---Y sub
>
> We'd expect to get this when we run "git subtree push -P sub . sub" on
> master at F:
>
> X---Y---E'--F' sub (after push, expected)
>
> But actually we get this (in Git 2.22.0):
>
> A---B---C---D'--E'--F' sub (after push, actual)
> /
> X---Y
>
> This seems to be a side effect of 2.7.0 -> 2.7.1 in which a change is
> made to include merged branches in "git subtree push", but mistakenly
> causes branches before "git subtree add --squash" be included.
