Why does local git merge share the same commit history as a branch but remote pull request does not?

Question

TL;DR

My question is: how do I get my local git merge behavior to resemble the way it works when I do a pull request from a branch back to main in GitHub, i.e. showing a branched commit history rather than a rebase-like history? I don't have it set to automatically do anything with rebase from what I can tell -- see details below.

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Here's the scenario:

1. The main branch is clean.
2. I perform git checkout -b test-branch.
3. I make a change to README.md; check in, publish branch to origin.
4. Another change to README.md; check in; repeat two more times (3 total local commits), push to origin. Here's what git graph shows:
   
   
5. Switch to main; merge test-branch from VS code menu:
   
   
   
   Then push to origin. Here's what git graph shows now:
   
   
   
   The result looks like a single line of commits as if it did a rebase (which I don't want).
6. Now I repeat steps 1 through 4 creating a new branch test-branch1. Here's what git graph shows:
   
   
7. Now, instead of merging the branches locally, I perform a pull request from the branch in GitHub:
   
   
8. Locally, I switch to main and pull from remote. Here's what git graph now shows:
   
   
   
   Now instead of looking like a rebase happened, it has a separate history.

My user gitconfig just has my name and email address, and here is what my repo git config looks like (i.e. no rebase setting from what I can tell):

So again, my question is how do I get my local merge behavior to resemble the way it works when I do a pull request from a branch back to main in GitHub, i.e. maintaining the separate commit history from the branch?

Answer 1

--no-ff flag in git prevents the execution of a "fast-forward" merge and it's the merge method that GitHub uses in pull requests. - reference.

git merge <branch-name> --no-ff
git pull <remote-name> <branch-name> --no-ff

You might consider --ff-only flag as well.