Question

It it safe to commit at branch A, branch a new branch B, amend last commit at A, leaving B with the new commit?

Answer 1

Amending a commit changes the tag of that commit. So branch B will have a new commit that branch A doesn’t have and branch A will have a new commit that branch B doesn’t have in this case. If you merge branch B back into A with a simple merge, your log in branch A will look like:

*    Merge from Branch B
|\  
| *  a change from Branch B
| *  commit related to xxx
* |  Amended commit related to xxx
|/  
*  Last commit before branching