A bit more details:
$ git clone --depth 1 --single-branch --branch master
https://github.com/git/git
$ cd git
Here, a shallow clone is made with just 1 commit.
$ git show -s --pretty=%P HEAD
Outputs nothing; that's already a small bug.
Surely the commit has parents!
$ git cat-file -p HEAD | grep parent
OK, that's better, finally the true parents are shown.
$ >1.txt
$ git add 1.txt
$ git commit --amend
Here, the top (and only in our clone) commit is amended.
$ git cat-file -p HEAD | grep parent
Nothing! This is the bug I'm reporting: amending the commit orphaned it.
To give a bit more background: I have a heavy-weight repo which I was
testing on different machines. Since it's heavy, I decided to shallow
clone just 1 commit. Upon testing on some machine, I found a small bug
and amended a fix. Then I force-pushed. I expected the branch to be amended.
Instead, what I got was an orphaned branch, disconnected from all repo's
branches, containing all files at once! Clearly not the best thing.
