Git commit hashes and Git merging between branches

Question

We have a scenario where we'd like to use two branches in our git workflow, otherwise known as develop and master.

The current flow is as follows:

• Create feat-branch - this branch will be based off of master.
• Make your changes in feat-branch, then finally commit your changes, and push them upstream to the remote feat-branch.
• Finally, the goal is you will eventually make two Pull Requests (via GitHub). One will be: develop <- feat branch and the other will be master <- feat branch

This methodology works perfectly fine for merging things into the master branch since the feature branch is already branching off of the master branch (aside from having to git pull origin master every now and then when you are out of date - but this is expected (I personally like to rebase my feature branches as well)).

However, the idea is you will be making a Pull Request to develop first (before you even make a secondary Pull Request to merge to master).

Merging to the develop branch becomes dicey at this point because each contributor is effectively making the same exact PR to both develop and master, which is creating different merge commit hashes in each respective branch with the same changes.

However, since everyone is branching off of master, this means those merge commits that end up in master eventually get merged back into the develop branch over time... this causes PRs to have erroneous differences being displayed which essentially say the same changes are being made by another person.

I'm guessing this is a mix of how commit hashes work in conjunction with the fact that every merge commit that is created after a Pull Request is merged into master ends up being included in a PR to the develop branch.

At this point I'm kind of just looking for maybe some sort of general direction or ideas regarding resolution, whether it be an entirely different way to approach the 2 branch model or something different altogether.

• mmathis: Why do you want to use two branches? Why would you merge feature branches to both at the same time?
• a clue: That just happens to be what's happening right now. I've pitched using one master branch and axing the other branch altogether. The goal of the 2 branch model was to ensure we had some sort of buffer before something went to master. Ideally you'd make a PR to develop ,test the changes, then eventually make the same PR from your feature branch to master.
• mmathis: Typically when one uses 2 branches (develop and master, usually) there is a release branch in between the two. You cut the release branch from develop, test it, tweak it, and then merge release into master in one fell swoop. How often do you merge feature branches, and how often to you release / deploy to production?
• a clue: There is no set schedule; everything just happens whenever someone is ready to merge a new feature in. The only exception to this rule is weekend / end of week merges into master are not allowed unless they're urgent bug fixes.
• joshp: It would help to have a clear statement of the problem or question, such as, How can we have a buffer before a change goes to master, without creating unnecessary merge complexity and conflicts?

Answer 1

To me it sounds from your description like your develop branch is actually an integration and testing (or QA) branch; and that your master branch is actually your production (or release) branch.

If so then your feature branches should be forked from develop, and the only person merging to master should be your release manager, and those merges should only ever come from the develop branch.

Answer 2

Either stick to develop as your primary branch, or gate pull requests to master with a test suite.

You are currently using master to represent your working, tested software, and develop to integrate different feature branches.

Your current process fails to do that well. By merging the feature branch separately into develop and master, there's the risk that the two target branches don't end up with the exact same state. Furthermore, due to the way Git works, merges become increasingly tedious as the branches diverge.

One way to address this is to only merge features into develop. When you feel ready, the current state of develop can be merged into master. This is effectively the Nvie Git-Flow, with all of its advantages and disadvantages. The Git-Flow is well suited for software with big, infrequent releases that need to be supported for some time in parallel.

A different approach is to merge all features directly into master. This is very easy and straightforward, but requires that the changes don't break anything – master should always be in a releasable state. The same people who invented Continuous Integration were also big on automated testing, to the degree that the two are now effectively synonymous. GitHub popularized pull-request based patterns, where the PR gives opportunity for manual reviews and automated testing.

Such PR-based approaches are a good fit when you have frequent small releases, especially in an SaaS or web context, and when bugs in the released version tend to be low-impact so that they can be fixed in a subsequent release (no hotfixes!). However, this requires a QA culture that has high confidence in the automatic tests. This doesn't necessarily mean 100% unit test coverage, but some integration tests for essential functionality and lints/static analysis to find potential problems. If you already have high converage, checks like "added lines must be covered by tests" can be useful.

Pull-request based approaches run into problems with large features that have diverged a lot from master, and with WIP changes that are not in releasable state. However, you can use refactoring patterns and feature toggles to make gradual changes without breaking anything and to only enable risky functionality once it feels ready. Sticking to such safe patterns and writing suitable tests requires some discipline and competency, though.