git subtree push --squash does not squash

Question

I am using git subtree to organize my git repositories. Let's say I have a main repository called repo and a library called lib.

I successfully "imported" the lib repository by squashing its history. I would now like to contribute back to lib by squashing the history too. This does not seem to work: I specify the --squash option to git subtree push but when looking at the history I still send all the commits.

How to reproduce

Here is a script showing the minimal commands needed to reproduce the problem:

#!/bin/bash
rm -rf lib lib-work repo

# repo is the main repository
git init repo
# lib is the 'subtreed' repository (bare to accept pushes)
git init --bare lib

git clone lib lib-work
cd lib-work
# adding a bunch of commits to lib
echo "v1" > README
git add README
git commit -m 'lib commit 1'
echo "v2" > README
git add README
git commit -m 'lib commit 2'
echo "v3" > README
git add README
git commit -m 'lib commit 3'
git push origin master
cd ..

cd repo
# adding initial commit to have a valid HEAD
echo "v1" > README
git add README
git commit -m 'repo commit 1'
git remote add lib ../lib
git subtree add --prefix lib lib master --squash
echo "v4" > lib/README
git add lib/README
git commit -m 'repo commit 2'
echo "v5" > lib/README
git add lib/README
git commit -m 'repo commit 3'
echo "v6" > lib/README
git add lib/README
git commit -m 'repo commit 4'
#git log --all --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s%Creset' --abbrev-commit
# "not working" command :
git subtree push --prefix lib lib master --squash

# pretty print the history
git log --all --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s%Creset' --abbrev-commit
cd ../lib
echo
git log --all --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s%Creset' --abbrev-commit

git log showing the problem

The output of the two git log blabla commands are:

* b075d5e - (HEAD, master) repo commit 4
* ebdc7c7 - repo commit 3
* 9f1edab - repo commit 2
*   3d48bca - Merge commit '34e16a547819da7e228f3add35efe86197d2ddcb' as 'lib'
|\
| * 34e16a5 - Squashed 'lib/' content from commit 2643625
* 3f1490c - repo commit 1
* 1f86fe3 - (lib/master) repo commit 4
* 9f1639a - repo commit 3
* 8bd01bd - repo commit 2
* 2643625 - lib commit 3
* 3d64b8c - lib commit 2
* aba9fcb - lib commit 1

and :

* 1f86fe3 - (HEAD, master) repo commit 4
* 9f1639a - repo commit 3
* 8bd01bd - repo commit 2
* 2643625 - lib commit 3
* 3d64b8c - lib commit 2
* aba9fcb - lib commit 1

As you can see, lib sees the "repo commit 2,3,4" although I specified the squash option. The other way around worked hence the Squashed 'lib/' content from commit f28bf8e.

I tried on windows with git version 1.8.1.msysgit.1 and on linux with git version 1.8.3.4.

So why doesn't the --squash option do a squash?

Side question

Why does lib/master appears in the log of the repo repository ? Knowing it appears only after the "failed" git push: if you uncomment the first git log blabla you get the following output showing the stashed history but no sign of lib/master :

* b075d5e - (HEAD, master) repo commit 4
* ebdc7c7 - repo commit 3
* 9f1edab - repo commit 2
*   3d48bca - Merge commit '34e16a547819da7e228f3add35efe86197d2ddcb' as 'lib'
|\
| * 34e16a5 - Squashed 'lib/' content from commit 2643625
* 3f1490c - repo commit 1

Answer 1

It is possible that this is an error in the documentation of the subtree command.

The manual in git states:

options for 'add', 'merge', 'pull' and 'push'
    --squash              merge subtree changes as a single commit

If you check the more extended documentation in the original subtree project you will notice that the --squash option is only explained for add and merge, as the functionality is described for the process of bringing content into your repository. Since pull is a modified form of merge, it is also implied that it can use --squash.

The push in the manual list what does not make sense. The git subtree push subcommand is a combination of git subtree split and git push. This means that --squash should be an option also supported by split, but split is not listed in the manual list. It is neither ever stated in the documentation that it can use --squash.

The --squash option is indeed accepted by split and push without error, but after experiment with it it seems it makes no difference, just as your example states. My take is that it is there by mistake and just ignored by the split and push commands.

Answer 2

This is now (Git 2.5, Q2 2015) confirmed in the official git subtree documentation.

See commit 6ccc71a by Danny Lin (danny0838), 07 May 2015.
^{(Merged by Junio C Hamano -- gitster -- in commit 6263f58, 22 May 2015)}

contrib/subtree: there's no push --squash

The documentation says that --squash is for 'add', 'merge', 'pull' and 'push', while --squash actually doesn't change the behavior of 'push'.
Correct the documentation.

--squash:

This option is only valid for add, merge, and pull commands.

---

With Git 2.29 (Q4 2020), the documentation for subtree (in contrib/) is clearer.

See commit ce820cb, commit f99c0c9 (18 Aug 2020) by Danny Lin (danny0838).
^{(Merged by Junio C Hamano -- gitster -- in commit 8923a45, 24 Aug 2020)}

contrib/subtree: document 'push' does not take '--squash'

^{Signed-off-by: Danny Lin}

git subtree push does not support --squash, as previously illustrated in 6ccc71a9 ("contrib/subtree: there's no push --squash", 2015-05-07, Git v2.5.0-rc0 -- merge listed in batch #4)

The documentation no longer mentions push.

Answer 3

I have found this thread because I just had the problem that the subtree push sends all the commits of the entire history of the parent repo and not just the ones regarding the newly added subtree. It turned out that the subtree cache was somehow corrupted due to a botched previous subtree add operation. I had to delete the .git\subtree-cache directory to fix the issue.