git merge, why no Fast-forward every time ?

Question

I make a branch (b1) from develop branch

git checkout -b b1

and make some commmits over b1

at same time, make some commits over develop, when I try merge the commit of develop over b1

git merge develop

the merge editor is open, and a no Fast-forward is make

d25ef61 Merge branch 'develop' into b1

why ?

Answer 1

A fast-forward merge happens when there are no new commits on the base branch, so that the commits you're merging can be appended directly.

Since you want to merge two different subtrees of commits together, you need a merge commit.

Alternatively, you can use git rebase to reproduce the new commits onto the base branch.
This will create a separate copy of each commit; use with caution.