git - Merge commit without squash vs with squash option

Question

On daily routine i use SmartGit as client of choose. My team members however stick to git native, non commercial GUI. We discovered some differences in how our merge commits looks like.

Those are options that SmartGit gives when requested to merge branch:

On below graph you can see my example SmartGit graph output, containing:

• single master branch
• One branch merged to master with merge commit option
• One branch merged with simple commit option

One of branches (with_merge_branch) is visualizing merge operation by joining branch with master via line. Second one (normal_commit_branch) does not.

Question is, how to enforce both behaviors in native git commands? I.e. whats the difference between those two commits?

Answer 1

The difference between the two kinds of merge are only different in the commit history (as you showed the logs in graph).

Let's illustrate by graphs. Assume the commit history as below before merging:

A---B---C---D  master
     
      E---F---G  develop

Merge commit (multiple parents):

The command used is git merge branchname. It's the default way to merge two branches.

When you merge develop branch into master branch by Merge commit in SmartGit (git merge develop), the commit history will be:

A---B---C---D---M  master
              /
      E---F---G    develop

Simple commit (one parent, "squash"):

It merges two branches with --squash option, the command used is git merge branchname --squash.

--squash

Produce the working tree and index state as if a real merge happened (except for the merge information), but do not actually make a commit, move the HEAD, or record $GIT_DIR/MERGE_HEAD (to cause the next git commit command to create a merge commit). This allows you to create a single commit on top of the current branch whose effect is the same as merging another branch (or more in case of an octopus).

When you merge develop branch into master branch by simple commit in SmartGit (git merge develop --squash), it get the changes from develop branch into master branch as a new ordinary commit (as if a real merge happened), and the commit history will be:

A---B---C---D---M  master
                      
      E---F---G    develop