Let's Stop Pretending that Source Control is "Optional but Recommended"

Essentially all of us who make our living from the craft of software development, early in our careers, have had the experience of losing source code that we couldn't get back. Oh, we could type what we remembered into a file of the same name, but it has important differences that we will discover as we work with it. (There is no such thing as eidetic, or photographic, memory).

This has been recognised as a sufficiently universal phenomenon that most developers and managers I have known in the lsat 10-15 years (at least) use use of a versioning system as a filter against dangerous dilettantes; if someone claims to have developed "the next VisiCalc for Linux" without using one, the file containing that person's "CV" may be safely deleted (and do remember to Empty the Trash).

So why on $DEITY's green Earth do we still see well-meaning tutorials on blogs the Internet over which include a step titled "Setup source control (Optional but recommended)"? The particular tutorial that drew my ire this morning even went out of its way to note that you will need to use a "text editor of your choice" with the author noting that "I use Emacs". (Subject and direct object inverted in the original sentence, but that's another rant.)

Don't

DO

that!!

The person reading your tutorial is probably going to be someone with strong continuing economic motivation to improve his software skills; he's reading your tutorial on the off chance that you'll actually teach him something useful. Seeing those three words ("optional but recommended") tells him, almost literally, that you don't really take him seriously. Your half-dozen other readers are going to be (would-be) apprentices in the craft, just learning their way around; they can and, based on experience, will take those three words as permission to just blaze on ahead and, when something goes pear-shaped, to start all over. Maybe you think "nobody I know would take it that way", or even "how could anybody who can read this take it that way", but The Voice of Experience™ is here to tell you that this Internet thingie is a global phenomenon. People from all walks of life, with every language, technical and educational level variation imaginable, can wake up one fine morning and say "I'm going to learn something new, using the Internet", and set out to do just that. That's a feature, not a bug.

I can hear you sputtering "but I didn't want to have to cover how to set up a VCS or use it in the tutorial's workflow; I just wanted to teach people how to use batman.js". Fair enough, and a noble goal; I don't mean to dissuade you (it's actually a pretty good tutorial, by the way). Might I suggest adding to the bullet list under "Guide Assumptions" a new bullet with text approximating

• A version control system of your choice (I use Foo)

with an appropriate value of Foo. We don't care whether the Genteel Reader uses git, Bazaar, sccs, or Burt Wonderstone's Incredible Magical VCS; we can merely assume that if he and we are worth each other's time, he's using something; we only need that little extra bit of reinforcement. (Though some choices on that list might be cause for grave concern.)

One of the ways in which the craft of software development needs to change if it's ever going to become a professional engineering discipline is that we're going to have to hammer out and apply a shared set of professional ethics; the closest we've got now is various grab-bag lists of "best practices". I'd argue that "optional but recommended" source control is on the wrong side of one of the lines we need to draw.

Playing Mind Games With git, And Seemingly Winning

I had some bad experiences with git a few years back, and until a year or so ago, you couldn't get me to touch it with a ten-parsec pole. Let's just say that things got lost… changes, files, jobs, companies, little things like that. So, building out a Rails shop over the last year, with git being The Standard™(thank you, Github), you'd think I'd be super-extra-hyper-careful about it, right?

Well, the training wheels have to come off sometime, and if they take rather important bits of your skull along for the ride, consider it a Learning Experience. You were warned, weren't you? You did read that .2-point type on the side of the tin with the big label LIFE! that said "Death will be an inevitable finale to Life. Don't bother the lawyers", didn't you? Oh, well. Details.

Rule #16,472 in Dickey's Secrets of Software Survival states: "Never write important code while seriously ill with flu or whatnot. The results would be worse than if you had written the code while drunk. In fact, you may want to give serious consideration to getting drunk before attempting to code while sick." Because what violating 16,472 can get you is shenanigans like committing great laundry lists of files, several times, only to find yourself staring at a red bar and wondering how you got there. (Hot the Red Bar in Cable Street in London, but the red bar that is your test tool saying "your code and/or your specs/tests are busted, bub". That red bar.) This has actually happened to me not once, but twice in the last couple of months.)

At which point, you mutter dark threats under your breath at the imbecile who put you in this position (yourself) and start retracing your steps. Whereupon you find that your last genuine, not-because-things-were-wildly-cached proven-working version was five commits earlier. Five commits that have been pushed to the Master Repo on Github earlier. You then note that each of these touched a dozen files or so (because you don't like seeing "19,281 commits" in the project window when you know you're just getting started), and a couple hours of spelunking (as opposed to caving) leaves you none the wiser. What to do?

The first thing to remember is that there is nothing structurally or necessarily semantically significant about the master branch in git. As far as I can tell, it's merely the name assigned to the first branch created in a new repo, which is traditionally used as the gold-standard branch for the repo. (Create new branch, do your thing, merge back into master. Lather; rinse; repeat. The usual workflow.) On most levels, there's nothing that makes deleting the master branch any different than any other.

Of course, the devil is in the details. You've got to have at least one other surviving branch in the repo, obviously, or everything would go poof! when you killed master. And remote repos, like Github, have the additional detail that specifies HEAD as the default branch on that remote. (Thanks to Jefromi for this explanation on StackOverflow, to another guy's question.) There always has to be a default branch; it's set to master when the repo is created and very rarely touched. But it's nice to know that you can touch, or maul, it when the need arises.

Here's what I did:

1. I went back to that last proven good commit, five commits back, and created a new repair branch from that commit;

2. I scavenged the more mundane parts of what had been done in the commits on master after the branch point, and made (bloody well) sure specs fully covered the code and passed;

3. I methodically added in the code pieces that weren't so mundane, found the bug that had led me astray earlier, and fixed it. This left me with a repair branch that was everything master would have been had it been working.

Now for the seatbelts-and-helmets-decidedly-off part.

4. I verified that I was on the repair branch locally;

5. I deleted the master branch in my local repo

6. I ran git branch master to create a new master branch. (Note that we haven't touched the remote repo yet);

7. I checked out the (new) master branch (which at this point is an exact duplicate of repair, remember);

8. I (temporarily) pushed the repair branch to origin;

9. I used the command git remote set-head origin repair to remove the only link that really mattered to the existing master branch;

10. I deleted the master branch on the remote ("origin") repo as I would any other remote branch;

11. I force-pushed the new master to the remote, using the command git push --force origin master. I needed the --force option to override git's complaint that the remote branch was ahead of the one I was pushing;

12. I ran git remote set-head origin master to restore git's default remote branch to what it had recently been; and

13. I deleted the repair branch from origin

Transmogrification complete, and apparently successful. Even my GUI git client, SourceTree, only paused a second or so before displaying the newly-revised order of things in the repo. It's useful to know that you can trade the safety scissors for a machete when you really do feel the need.

However… so can anyone else with access to the repo. And I can easily see scenarios in a corporate setting where that might be a Very Bad Thing indeed. In a repo used by a sizeable team, with thousands of commits, it wouldn't be all that difficult for a disgruntled or knowingly-soon-to-be-disgruntled team member to write a program that would take the repo back far enough into the mish-mashed past to deter detection, create a clandestine patch to a feature branch that (in the original history) was merged into master some time later, and then walk the commits back onto the repo, including branches, before pushing the (tainted) repo back up to origin. I'd think that your auditing and SCM controls would have to be pretty tight to catch something like that. I'd also think that other DVCSes such as Mercurial or Bazaar would have a much harder time successfully doing what I did, and therefore, would be less likely to such exploitation. That this hasn't been done on a scale wide enough to be well-publicised, I think, speaks quite loudly about the ethics, job satisfaction, and/or laziness of most development-team members.

What do you think?