GIT merge --no-ff

Question

In this post I will someone expert on git try to explain how git merge --no-ff can help us. I have read here http://nvie.com/posts/a-successful-git-branching-model/ (which I personally found to be a really good post) that git merge --no-ff: "This avoids losing information about the historical existence of a feature branch and groups together all commits that together added the feature". So I found it really useful and make some experiments.

The problem is about how can we know from the git log information which commits belong to each feature. For that I did the next experiment. Suppose two users are developing on a software project two different and independent feature (to avoid merge conflicts). From the last stable version we will proceed as this:

git init touch AAA.txt git add AAA.txt git commit -m "My stable software version" //this will simulate our project repository

So from this point the two user (name Alice and Bob) create two different branches and start working on the features:

git branch feature1_Alice git branch feature2_Bob And now Alice and Bob start working and commiting simultaneously. We could simulate his as:

git checkout feature1_Alice touch f1_A1.txt git add f1_A2.txt git commit -m "Solving little bug on feature 1" Bob do two commits following timeline after Alice does this one:

git checkout feature2_Bob touch f2_B1.txt git add f2_B1.txt git commit -m "Starting feature 2" touch f2_B2.txt git add f2_B2.txt git commit -m "feature 2: implementing new functionality" Then Alice finish feature:

git checkout feature1_Alice touch f2_A3.txt git add f2_A3.txt git commit -m "Feature 1 finished"

Then Bob finishes feature2:

git checkout feature2_Bob touch f1_A3.txt git add f1_A3.txt git commit -m "Feature 2 finished"

Now we merge the new feature to the main branch:

git checkout master git log Output:

commit c58dd35054f83c089292d090781438f37feeffa3

Author: Juan

Date: Tue Apr 25 10:30:01 2017 +0200

My stable software version

git merge --no-ff feature1_Alice //We put a message on the created commit

Now git log outputs:

commit 50c5d1570fe0c047f72200bd57ef6cef6fa9077e Merge: c58dd35 c136a23 Author: juan Date: Tue Apr 25 10:48:12 2017 +0200

Merging feature 1 to main
Merge branch 'feature1_Alice'

commit c136a23c49c546e5f48d9d0634e9bc51d67370cd Author: juan Date: Tue Apr 25 10:41:49 2017 +0200

Feature 1 finished

commit c9dbb1b49444555fca528f562d3a38143fd521e9 Author: juan Date: Tue Apr 25 10:35:24 2017 +0200

Solving little buf on feature 1

commit 58afad2b46565e614a99d94d1e1aa1c8520f9f2b Author: juan Date: Tue Apr 25 10:35:01 2017 +0200

Starting feature 1

commit c58dd35054f83c089292d090781438f37feeffa3 Author: juan Date: Tue Apr 25 10:30:01 2017 +0200

My stable software version

And finally merge feature 2:

git merge --no-ff feature2_Bob git log commit 3f27f78fefb30080ace629e561a242a4f8dbca56 Merge: 50c5d15 2eee0c1 Author: juan Date: Tue Apr 25 10:54:20 2017 +0200

Merging feature 2 to master
Merge branch 'feature2_Bob'

commit 50c5d1570fe0c047f72200bd57ef6cef6fa9077e Merge: c58dd35 c136a23 Author: juan Date: Tue Apr 25 10:48:12 2017 +0200

Merging feature 1 to main
Merge branch 'feature1_Alice'

commit 2eee0c1bb732443ae7d6f4893d651abfd558d55a Author: juan Date: Tue Apr 25 10:43:14 2017 +0200

Feature 2 finished

commit c136a23c49c546e5f48d9d0634e9bc51d67370cd Author: juan Date: Tue Apr 25 10:41:49 2017 +0200

Feature 1 finished

commit cd3bee2906e02df22866ba710891d21eaebb8013 Author: juan Date: Tue Apr 25 10:40:12 2017 +0200

feature 2: implementing new functionality

commit c6fdf092b2645f7d4088f9f439e820a9a820b891 Author: juan Date: Tue Apr 25 10:37:39 2017 +0200

Starting feature 2

commit c9dbb1b49444555fca528f562d3a38143fd521e9 Author: juan Date: Tue Apr 25 10:35:24 2017 +0200

Solving little buf on feature 1

commit 58afad2b46565e614a99d94d1e1aa1c8520f9f2b Author: juan Date: Tue Apr 25 10:35:01 2017 +0200

Starting feature 1

commit c58dd35054f83c089292d090781438f37feeffa3 Author: juan Date: Tue Apr 25 10:30:01 2017 +0200

My stable software version

Could anyone tel how can I see from the commit history and merge commit which commits influence each feature? I cannot see the advantage commented in that web when we insert alternative commits from different features (or from a feature and master) in time.

The only difference in using --no-ff is that the merge commit have information of which commits have been merged, but that is unseful for tracking the commit history.

Thanks in advance.

Answer 1

You can take a look at your repository graph with git log --graph --oneline --decorate --all or just call gitk to visualize your history. The linear text version provided by a simple git log will not show the information you're looking for.

When looking at the graph representation, merge commits ensure you can see where two branches meet, while a fast forward merge would result in different branches being shown as linear although they were developed in parallel.