# Where parallels cross

Interesting bits of life

# Emacs as your code-compass: let history show you which files to edit next

Emacs can suggest you what file to modify next according to your repository history. Just get code-compass run c/find-coupled-files on a file in your Git repository!

## The problem

In a previous post I have shown how we can look at modules relations via a graph. The idea was to find more easily modules that need to change together and to give you visibility on modules that should be independent but that are still coupled according to historical change patterns.

Now, a graph is useful as an overview, but what about while we are coding? As I was saying in my previous post, sometimes I forget to change some important file causing myself rework and delivery delays. The terrible thing is that my repository history can tell me what to do! How nice would it be if Emacs could directly tell me what to change next?

## It is a problem indeed

There is some momentum for text editors to become smarter and make life easier for the developer. Ideally, as Gregory T. Brown explores in the last chapter of his book Programming beyond practice, we should replace low-level tools with more advanced tools which make us feel closer to our work: imagine focusing only on understanding your clients problems, and then in a few knowledgeable inputs shave off the rough solution of our computer to fit our client requirements perfectly. Instead we get side tracked by that recursion that is overflowing our stack 1.

This is still a bit far away as far as I know. It would be cool, though, if we could move Emacs a step closer to that side of things. At least, let's make it learn from our Git history!

## And there is a solution

Until we get to the point where our computer Emacs does most of the plumbing work for us, let's integrate the data of that fancy graph I showed you earlier into our find-file!

This is how code-compass latest feature looks like:

In the above we generate a cache that stores for each project you visit a list of coupled files. When the cache is ready we can use c/find-coupled-files. If the file has no significant history, a message lets us know that no file was found. Otherwise, it provides a list of coupled files sorted by amount of changes and relevance: so the first proposed file is surely what you want to change next.

(Now that I think of it, I should probably introduce an optional toggle that if on discards files if you have already changed them: in that way you could use this choice as a todo list for your change.)

Anyway, I surely cannot remember to produce the cache while I am working on something. For that reason, I set a hook appositely for that in my configuration:

(run-with-timer 10 nil (lambda () (add-hook 'projectile-find-file-hook 'c/get-coupled-files-alist-hook-fn)))


I use projectile, and I thought that the best moment for me to create the cache is when I open a new file through projectile. Due to some initialization error, I delay the setting of that hook in my configuration: I run a timer to set the hook after 10 seconds Emacs initialized.

On the long run I plan to focus my code-compass work more towards this direction, because I think the repository history can give us much more value than this. I am still experimenting and designing things, but hopefully this gives you a taste of what is coming.

## Conclusion

So get code-compass and let it help you finding out which files is best to change after the one at hand! You just need to run c/find-coupled-files on a file in the current project, and set a hook if you do not want to wait.

Happy coding!

## Footnotes:

1

by the way, use the fold/reduce operation if you are having recursion problems, because working with explicit recursion is mostly for learning purpose