了解 git diff 和 git cherry-pick 的工作原理

Question

Here is the repro repo: https://github.com/sathishsoundharajan/git-diff

Steps

1. Created new repository in github.
2. Created master branch.
3. Added master.txt file to master branch and committed.
4. Created new branch named feature-branch from master.
5. Added feature.txt file to feature branch and committed.
6. Switch to master branch.
7. Added a new file new-master.txt to master branch and committed ( CommitId: https://github.com/sathishsoundharajan/git-diff/commit/593da755a9ea90b6f55bcc6d184f249218bf4170 )
8. Now for some reason let's say i have to cherry-pick this commit to feature-branch.
9. Switch to feature-branch.
10. Use git cherry-pick 593da755a9ea90b6f55bcc6d184f249218bf4170 . Cherry-picked without conflicts but the commit_id changed to https://github.com/sathishsoundharajan/git-diff/commit/e58427c82322d6a3ec933741887f5b8312981e11
11. Now if we raise a pull request from feature-branch to master / take git diff between master and feature-branch, i should only see the feature.txt file alone in the diff. But i can see new-master.txt file also in the diff https://github.com/sathishsoundharajan/git-diff/pull/1

Questions:

1. Why commit-id changed after cherry-pick ?
2. Can we stop cherry-pick to not create new commit-id and reuse the existing one ?
3. Why in git diff i'm seeing new-master.txt even though it is already in the master branch ?
4. Is there way to make git does not show this diff ?
5. Is there a way to see diff between two branches without comparing commit-ids and by comparing actual change in the files ?

Answer 1

1 because history is different so the IDs can't be the same for security/cryptographic reasons.

2 no, related ro #1 ... if you got the same ID, that would mean you found a collision (or you are producing the exact same objects, like what git svn does)... theoretically possible but....

3 because in PR/MR, you see differences not between the tips of the two branches but since the feature branch is started , say (what you get if you try git diff with ... instead of .. ). If you saw the differences between the 2 tlps of the branches, code review would be hell because you would see changes from the MR/PR itself plus the changes introduced in the target branch since the MR/PR branch was started (not to name that the changes will change over time as more stuff is merged unto the target branch). Who would want to work like that?

4 like the diff betwern the 2 branch tips? Try with .. instead of ... . Now, on github? They might provide the option if they considered it necessay but I don't think you will find a lot of customers would be interested.... and then it's about them, not about git.

5 what do you mean?