Last few months, I've occasionally needed to run emacs on Windows. In a previous post I wrote about how I got my emacs config to work on Windows, which initially seemed sufficient. But every time I switch from Linux (or even MacOS) to Windows, I notice new sluggishness in some or the other component! Most recently, it was projectile.

Have you ever experienced typing a command on a remote server over a slow SSH connection? Muscle memory doesn't just involve your fingers recalling commands and key bindings—it works on the entire sequence of actions you intend to perform. When I press the keybinding to find file in a project, my fingers have already moved on to the next steps i.e. quickly filtering the results and hitting enter. I anticipate the file list to appear almost instantaneously, and if there's a lag of even a few seconds, it's frustrating and not a mere inconvenience.

To make it worse, the project I was working on had a large number of files. The delay in displaying the file list was a bit too much to deal with. I had to drop everything else and fix it on priority!

After going through the projectile documentation and some tinkering I was able to solve it rather quickly (all thanks to the well written docs). The answer lies in projectile's default config for indexing files on Windows v/s Unix-like platforms. Here indexing means compiling the list of files from the project that the user may want to open. You can inspect the projectile-indexing-method variable to check which method is currently in use.

The default indexing method is alien on all operating systems, except on Windows where it's native. The native indexing is implemented in emacs lisp and hence is portable i.e. works on all platforms. The alien indexing method on the other hand shells out to external tools such as git or find to obtain the list of files from the project. For e.g. if your project uses git for version control, it asks git to provide the list of files. An advantage of this method is that your .gitignore file will be automatically considered.

native indexing can be much slower on projects that contain many files and deeply nested directories and setting it to alien can speed it up significantly in those cases. But the problem is that alien requires Unix tools that are not expected to be installed Windows, which is the reason why it's not set as the default.

But that doesn't mean you can't use alien on Windows. You can install Cygwin or something similar which provides the required Unix and GNU tools for Windows.

choco install Cygwin

Here I am using Chocolatey to install Cygwin.

Make sure that the binaries are accessible on PATH. In my case Cygwin was already installed but wasn't on PATH. To do so, you may permanently edit the PATH environment variable from Advanced System Settings. But I prefer to set it inside emacs itself:

(setenv "PATH"
        (concat
         (getenv "PATH")
         ";"
         "C:\\tools\\cygwin\\bin"))

Notice that the delimiter on Windows is a semicolon ; and not colon : as in case of Linux.

All that remains now is to set the indexing method to alien:

(setq projectile-indexing-method 'alien)

And that should fix the sluggishness. But there is scope for further optimization through caching. When the indexing method is native, projectile implicitly enables caching. This means by changing it to alien we've also unintentionally disabled caching. So enable it explicitly.

(setq projectile-enable-caching t)

If your project has an unusually large number files, you may also set it to persistent which will persist the cache on disk so that it can be used across emacs sessions.

If you use the same config on multiple OSs, you may add all this windows specific code conditionally as follows,

(when (eq system-type 'windows-nt)
  (setenv "PATH"
          (concat
           (getenv "PATH")
           ";"
           "C:\\tools\\cygwin\\bin"))
  (setq projectile-indexing-method 'alien)
  (setq projectile-enable-caching 'persistent))

References

• Projectile documentation