git-clone --single-branch clones objects outside of branch

[Chris Jerdonek <chris.jerdonek@gmail.com>]

Hi,

I'm reporting some git-clone behavior regarding --single-branch that I
found unexpected after reading the docs. I'm using git 2.25.0.

The git-clone docs for --single-branch say:

> Clone only the history leading to the tip of a single branch, either specified by the --branch option or the primary branch remote’s HEAD points at.

(from: https://git-scm.com/docs/git-clone#Documentation/git-clone.txt---no-single-branch
)

However, when I attempted this with a local repo, I found that objects
located only in branches other than the branch I specified are also
cloned. Also, this is true even if the remote repo has only loose
objects (i.e. no pack files). So it doesn't appear to be doing this
only to avoid creating new files.

In contrast, git-fetch behaves as expected (including locally).
git-fetch appears to fetch only objects in the given branch, when a
branch is specified.

Below are some commands to assist with reproducing this situation (but
you will need to update the path in the `git-remote add` invocation
below). At the least, it seems like the docs should clarify the
behavior. (The Python commands were for when I was doing some
experiments with pack files.)

mkdir repo1
cd repo1
git init
python -c "print('a\n' + 10 * 'x\n')" > a.txt
git add a.txt
git commit -m "add a"
# Get object id to check existence with `git cat-file -t` below.
git hash-object a.txt

git checkout -b dev
python -c "print('b\n' + 10 * 'x\n')" > b.txt
git add b.txt
git commit -m "add b"
# Get object id to check existence with `git cat-file -t` below.
git hash-object b.txt

git checkout master

cd ..
mkdir repo2
cd repo2
git init
git remote add other file:///<path-to-repo1>
git fetch other master

cd ..
git clone --branch master --single-branch repo1 repo3

Thanks,
--Chris