Git merge vs the worldI’ll be talking about git merge system again, one of the strongest on the planet, and how a good merge system can unlock a new world of possibilities for developers facing complex refactors. And then, I’ll tell you how to break it. And what can be done.
Refactor and mergeWhat does refactor have to do with merge? Aren’t merging and refactors on different planets?
Not at all: you’re working on a refactor and then you need to move Class.java to a new package. It happens, doesn’t it?
But while you’re working on your refactor, I’ll be tweaking Class.java.
Ok, now refactor has to do with merging, and if you’re avoiding this situation it only means one thing: you don’t have a proper SCM (we could argue but, ok, tell me you do not need a mouse, a good IDE…).
The good, the bad and the uglyNow you’ve to merge the previous scenario. What will happen?
Let’s break itLet’s do something else: you move and modify Class.java. But I do the same… moving it (of course!) to a different location.
Don’t do this at home with SVN: ok, the movie is over from the non-dvcs/non-merging scms, let’s focus on the real mergin machines.
Git it!How does Git handle it?
$ git commit -a -m "initial" Created initial commit ced4e21: initial 1 files changed, 181 insertions(+), 0 deletions(-) create mode 100644 foo.cs $ git branch task001 $ git checkout task001 Switched to branch "task001" $ vi foo.cs $ git mv foo.cs bar.cs $ git commit -a -m "change on task001 + rename" Created commit d3c6970: change on task001 + rename 2 files changed, 181 insertions(+), 181 deletions(-) create mode 100644 bar.cs delete mode 100644 foo.cs
First move and change, let's go to the second.
$ git checkout master Switched to branch "master" $ vi foo.cs $ git mv foo.cs moo.cs $ git commit -a -m "change on master + rename" Created commit 4644cb7: change on master + rename 2 files changed, 182 insertions(+), 181 deletions(-) delete mode 100644 foo.cs create mode 100644 moo.cs $ git merge task001 CONFLICT (rename/rename): Rename "foo.cs"->"moo.cs" in branch "HEAD" rename "foo.cs"->"bar.cs" in "task001" Automatic merge failed; fix conflicts and then commit the result.Ok, git nows about but... how does it handle it?
$ git status # On branch master # Changed but not updated: # # unmerged: bar.cs # unmerged: foo.cs # unmerged: moo.cs # modified: moo.cs # no changes added to commit $ ls bar.cs moo.csOoooops! The files are not merged and you’ve to solve the conflict yourself!!!
Plastic it!Is there a better way?
Yes: the dvcs should:
And that’s what Plastic SCM does.