Git Notes

This will be a continual work in progress and a testament that I should have made this post over a decade ago.

Dedicated fast-forward merge post of mine.

Reminders: the “index” is what holds staged changes. Useful site for undoing/recovering stuff: https://dangitgit.com .

This post and a lot advice and help for git on the internet assumes the command line.  That is because the git command line is same for everyone and easy to give precise instructions.  But really you should try to do as much as possible inside a nice git gui, possibly your IDE or SourceTree.  A nice git gui makes it easy to go from "I want to ..." to "I did it" by exploring menus and possibly right clicking items instead of looking up weird commands and syntax that you will soon forget.  A nice git gui also makes it much easier to see and understand your current repo state and its history.

Git Fast-Forward

Fast-forward merges have properties that are tightly tied together (basically they are equivalent)...

• A fast-forward merge is exactly the sort of merge that doesn't create a merge commit (assuming that you aren't doing destructive operations on commit history).
• A fast-forward merge is exactly the sort of merge that just updates the branch pointer. (Remember that `git pull` first does a `fetch` to get the remote commits before the merge happens, so a merge "just updating the branch pointer" can involve commits that didn't exist locally until the fetch.)
  
• A merge is fast-forwardable exactly when the source commit history is a superset of the destination branch commit history.
• A merge is fast-forwardable exactly when the destination commit is an ancestor of the source commit.

A note on terminology.  I have looked for the most official term for merges that are not fast-forward merges; these are the classical merges that create a merge commit.  The closest I have found is "true merge" as a git-merge reference section header.  Some people use the term "3-way merge" for all merges that create a merge commit, but 3-way merges are an algorithm for producing merge output where you also look at the most recent common ancestor of the two things you are merging, thus the name having "3" in it.  True merges do not have to use the 3-way merge algorithm (see merge strategies).  Thus, I will be using "true merge" or "non-fast-forward merge" to refer to merges that create a merge commit.