Git分支合并疑问：master合并至dev的结果及后续操作咨询

Let me walk you through this step by step—Git merging logic is straightforward once you visualize the commit history.

1. What happens when you merge master into dev? #

When you run git checkout dev && git merge master, Git does two main things:

• If there are no conflicts between the latest commits on master and dev, it creates a new merge commit (let's call this F' as you mentioned). This commit ties together the entire history of both branches: it has two parent commits—one from the latest master state, and one from the latest dev state before the merge.
• After the merge, dev's HEAD will point directly to this new F' commit. Meanwhile, master stays exactly where it was before the merge (its HEAD doesn't move unless you explicitly update it).
• If there are conflicts (e.g., both branches changed the same line in a file), Git will pause the merge and ask you to resolve those conflicts manually before you can finalize the F' commit.

2. Can you just merge dev back into master afterward? #

Short answer: Yes, but only if dev is ready for production/stabilization. Here's the context:

• Typically, dev is a branch for ongoing development, while master is your stable, production-ready branch. So you should only merge dev back to master once the code on dev has been tested, reviewed, and confirmed to be stable.
• Before merging dev to master, it's a good practice to pull the latest changes from remote master into your local dev first (again, git pull origin master on dev) to catch any new changes that might have been pushed to master since your last merge. This ensures you resolve any conflicts in dev before affecting master.

3. Will master's HEAD move directly to F' when merging dev back? #

This depends on whether master has new commits since you merged it into dev:

• Case 1: No new commits on master
  If master hasn't been updated at all since your merge to dev, Git will perform a fast-forward merge. That means it simply moves master's HEAD straight to F'—no new merge commit is created, because master's latest commit is already an ancestor of F'.
• Case 2: New commits on master
  If someone pushed new commits to master (e.g., E → G) after your initial merge to dev, Git will create a new merge commit (let's say G') when you merge dev to master. In this case, master's HEAD will point to G', not F'—since G' combines the latest master changes (G) with dev's changes up to F'.

Quick Step-by-Step Workflow to Follow #

• Update dev with master changes:

  git checkout dev
  git pull origin master  # Fetch and merge latest master into dev
  # Resolve conflicts if any, then commit
  

• Test and validate dev to ensure stability
• Merge dev back to master:

  git checkout master
  git pull origin master  # Make sure local master is up to date
  git merge dev           # Merge dev into master
  # Resolve conflicts if any, then commit
  git push origin master  # Push updated master to remote
  

内容的提问来源于stack exchange，提问作者weijia_yu