CODEWITHSUNDEEP
gitmergefast-forward
Georg Jähnig
Georg Jähnig

Reputation: 799

Git: setting merge.ff breaks fast-forward merges forever

I encounter a very weird problem in Git (version 2.10.1 (Apple Git-78)).

It seems that if I once set merge.ff to false in the local repo config, there is no way back for this repo. I just cannot unset it.

Here are the steps to reproduce:

git init

# Set merge.ff
git config --add merge.ff false

# Add some content and commit.
echo '.' >> file.txt
git add file.txt
git commit -am "commit"

# Create a new branch.
git branch feature

git checkout feature
echo '.' >> file.txt
git commit -am "commit"
git checkout master
git merge feature

This merge creates a commit with message - as expected.

Now I unset the setting, and I expect that future fast-forward commits will create no extra commits. But surprisingly, that does not work.

git config --unset-all merge.ff

git checkout feature
echo '.' >> file.txt
git commit -am "commit"
git checkout master
git merge feature

I'd assume this merge should not create a commit, because there is no merge.ff setting, so the default should apply. But the commit gets created.

What I want: Having fast-forward commits working again in my repo. Is there a way to get this?

Upvotes: 1

Views: 158

Answers (1)

torek
torek

Reputation: 488453

I'd assume this merge should not create a commit, because there is no merge.ff setting, so the default should apply. But the commit gets created.

The default is to fast-forward if possible, otherwise to make a merge commit.

A merge commit is necessary now, because the graph looks like this:

* 4667bf7 (feature) commit
| *   6663675 (HEAD -> master) Merge branch 'feature'
| |\  
| |/  
|/|   
* | c12b7b3 commit
|/  
* 3c62604 commit

The merge base of master and feature is commit c12b7b3...:

$ git merge-base master feature
c12b7b3f68caf419c3088fae293c57cfed147f34

and the tip of feature is 4667bf7, with the tip of master being 6663675. Neither of these two tips is equal to the merge base, so a merge is required.

Your configuration is OK:

$ git config --get merge.ff
$ cat .git/config
[core]
    repositoryformatversion = 0
    filemode = true
    bare = false
    logallrefupdates = true
[merge]

(It's rather obnoxious, but harmless, that git config leaves a bogus empty [merge] section in there; every additional git config merge.<whatever> adds another one when there's an empty one.)

Upvotes: 2

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