Integrating Baloo File Search with Emacs

I use KDE on the desktop. Although most of my userland operations are done in Emacs and Firefox, I tend to appreciate the choice when handling tasks more complex than text-based processes. KWin, the default window manager, features a superb set of per-application rules that come in handy while playing games, like forcing borderless fullscreen or always keeping a window on top. Plasma is stuffed to the brim with features and hooks, and I've exploited them before when writing my first Emacs package to ease certain operations between Emacs and my mobile devices. But one feature I've always missed has been desktop search. KDE offers the excellent Baloo, a file indexer that handles both metadata and content, and its integration with Krunner is the main reason I use the latter. As a matter of fact, despite Krunner's many features, like arithmetic and dictionary lookups, I only ever use it for finding files and launching applications. I can improve this workflow.

When opening a file, Krunner launches a new instance of the filetype's default program. This is sensible. If I open a PDF, I probably want Okular, and if I need to check an old web page, Firefox is the appropriate tool. But if I'm working in Emacs, there's tremendous value to staying in Emacs. Further, instead of opening a new instance of Emacs for text files, a within-Emacs solution lets me simply visit the file in a new buffer.¹ As the piece de resistance, I get to use Counsel for completion instead of Krunner.

As I discovered when writing kdeconnect.el, Emacs and Emacs Lisp make for an interesting programming experience. Unlike Java's extensive libraries and Python's convenience, writing Emacs Lisp makes me yearn for quality of life functions. Fortunately, the code to use Baloo for file searches form Emacs is basic enough that Emacs does abstract away much of the nitty gritty. Some of these functions I already knew (completing-read to let Emacs handle completion, split-string to take shell output and make a list, mapconcat and shell-quote-argument to generate safe shell commands), but others were novel to me and a massive relief to discover in the docs, like butlast to remove the last line of output, which contains the search's time to execute, or safe-length-query to check if a list is empty. Here's the resulting code:

(defun baloo-search (query)
  "Search for files matching QUERY using Baloo."
  (interactive "MSearch: ")
  (setq query (butlast
               (split-string
                (shell-command-to-string
                 (mapconcat 'identity
                            (list "baloosearch"(shell-quote-argument query))
                            " ")) "\n" t) 1))
  (if (eq (safe-length query) 0)
      (error "No matches"))
  (find-file (completing-read
              "Select file: "
              query
              nil t "")))

Pop that in your init.el or evaluate it somewhere and you're good to go! Call M-x baloo-search, enter your search term(s), which can include an extension, and choose your file. I've found this to be incredibly useful when I don't know quite where a file is or what it's called, and perhaps you will too.

Update 2019-05-31 Per request, should anyone be interested in modifying or extending this program, I hereby license it under the GPLv3.