affe.el - Asynchronous Fuzzy Finder for Emacs

This package provides an asynchronous fuzzy finder similar to the fzf command-line fuzzy finder, written in pure Elisp. A producer process is started in the background, e.g., find or grep. The output produced by this process is filtered by an external asynchronous Emacs process. The Emacs UI always stays responsive since the work is off-loaded to other processes. The results are presented in the minibuffer using Consult, which allows to quickly select from the available items. Note that Affe is an experimental package and a demonstrator of asynchronous processing outside of Emacs in a separate process. Generally I recommend to use consult-grep or consult-ripgrep, since these commands will perform better for large projects. The Consult package itself is more mature.

Installation and Configuration

The package is available on MELPA and can be installed using the Emacs package manager. If files should not be automatically previewed, a manual preview key should be set for affe-grep.

(use-package affe
  :config
  ;; Manual preview key for `affe-grep'
  (consult-customize affe-grep :preview-key "M-."))

The default regular expression transformation of Consult is limited. It is recommended to configure Orderless as affe-regexp-compiler in Consult.

(defun affe-orderless-regexp-compiler (input _type _ignorecase)
  (setq input (orderless-pattern-compiler input))
  (cons input (apply-partially #'orderless--highlight input)))
(setq affe-regexp-compiler #'affe-orderless-regexp-compiler)

Affe requires the rg (“ripgrep”) command line program to be available. The producer processes can be customized by adjusting the variables affe-find-command and affe-grep-command.

Available commands

• affe-grep: Filters the content of all text files in the current directory, similar to consult-grep.
• affe-find: Filters the file paths of all files in the current directory, similar to consult-find.

Related packages

Affe depends on Consult and works best with the Vertico and the Mct completion UIs.

• Consult: Useful search and navigation commands (Dependency of Affe).
• Marginalia: File annotations in the minibuffer.
• Embark: Minibuffer actions on files.
• Orderless: Advanced completion style, can be plugged together with Affe.
• Vertico or Mct: Vertical completion systems

Details

The Affe frontend transforms the input string to a list of regular expressions by calling the affe-regexp-function. The regular expressions are passed to the Affe backend via the emacsclient protocol. The backend controls a producer process, which generates lines of text. The lines are filtered using the regular expressions submitted by the frontend. For performance reasons, all-completions is used for the filtering. The backend returns only a limited amount of matching candidates, hopefully the most plausible ones. The frontend calls the affe-highlight-function on the returned matches, to highlight the input pattern.

Affe uses a more primitive matching technique than fzf, which uses the Smith-Waterman algorithm. Affe does not perform any ranking or sorting; it matches the lines in the order returned by the producer process against a list of regular expressions. On the upside, this allows plugging Affe together with the Orderless completion style, which can give a consistent fuzzy filtering experience across all Emacs commands, including synchronous and asynchronous commands.

As possible enhancement of Affe, one could implement alphabetical and sorting by length in the backend. By using a bucket sorting technique the sorting complexity will stay sufficiently linear such that the performance impact should be acceptable. However implementing a scoring-based sorting is probably not feasible since this requires heavier computations in Elisp. But maybe nativecomp Emacs is a game changer here?

Alternatives

• consult-grep/consult-find: Perform the filtering in the frontend.
• counsel-fzf: Ivy-specific, restarts find+fzf when updating the input pattern.
• fzf.el: Runs the fzf command line program in an Emacs terminal
• fuzzy-finder.el: Similar to fzf.el