GNU-devel ELPA - mct

Copyright (C) 2021 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”

(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

Minibuffer and Completions in Tandem, also known as “MCT”, “Mct”, mct, or mct.el, is a package that enhances the default minibuffer and *Completions* buffer of Emacs 28 (or higher) so that they work together as part of a unified framework. The idea is to make the presentation and overall functionality be consistent with other popular, vertically aligned completion UIs while leveraging built-in functionality.

The main feature set that unifies the minibuffer and the *Completions* buffer consists of commands that cycle between the two, making it seem like they are part of a contiguous space (Basic usage).

MCT tries to find a middle ground between the frugal defaults and the more opinionated completion UIs. This is most evident in its approach on how to present completion candidates. Instead of showing them outright or only displaying them on demand, MCT implements a minimum input threshold as well as a slight delay before it pops up the *Completions* buffer and starts updating it to respond to user input.

MCT is highly configurable to adapt to the varying needs of users. This section documents each user option.

This section outlines the various patterns of interaction that MCT establishes.

Minimal setup for the minibuffer and in-buffer completion:

(require 'mct)
(mct-mode 1)

And with more options:

(require 'mct)

(setq mct-completion-window-size (cons #'mct-frame-height-third 1))
(setq mct-remove-shadowed-file-names t) ; works when `file-name-shadow-mode' is enabled
(setq mct-hide-completion-mode-line t)
(setq mct-completing-read-multiple-indicator t)
(setq mct-minimum-input 3)
(setq mct-live-completion t)
(setq mct-live-update-delay 0.6)

;; This is for commands or completion categories that should always pop
;; up the completions' buffer.  It circumvents the default method of
;; waiting for some user input (see `mct-minimum-input') before
;; displaying and updating the completions' buffer.
(setq mct-completion-passlist
      '(;; Some commands
	Info-goto-node
	Info-index
	Info-menu
	vc-retrieve-tag
	;; Some completion categories
	imenu
	file
	project-file
	buffer
	kill-ring
	consult-location))

;; The blocklist follows the same principle as the passlist, except it
;; disables live completions altogether.
(setq mct-completion-blocklist nil)

(mct-mode 1)

Other useful extras from the Emacs source code (read their doc strings):

(setq completion-styles
      '(basic substring initials flex partial-completion))
(setq completion-category-overrides
      '((file (styles . (basic partial-completion initials substring)))))

(setq completion-cycle-threshold 2)
(setq completion-ignore-case t)
(setq completion-show-inline-help nil)

(setq completions-detailed t)

(setq enable-recursive-minibuffers t)
(setq minibuffer-eldef-shorten-default t)

(setq read-buffer-completion-ignore-case t)
(setq read-file-name-completion-ignore-case t)

(setq resize-mini-windows t)
(setq minibuffer-eldef-shorten-default t)

(file-name-shadow-mode 1)
(minibuffer-depth-indicate-mode 1)
(minibuffer-electric-default-mode 1)

;; Do not allow the cursor in the minibuffer prompt
(setq minibuffer-prompt-properties
      '(read-only t cursor-intangible t face minibuffer-prompt))

(add-hook 'minibuffer-setup-hook #'cursor-intangible-mode)

;;; Minibuffer history
(require 'savehist)
(setq savehist-file (locate-user-emacs-file "savehist"))
(setq history-length 500)
(setq history-delete-duplicates t)
(setq savehist-save-minibuffer-history t)
(add-hook 'after-init-hook #'savehist-mode)

;;; Third-party extensions

;;;; Enable Consult previews in the Completions buffer.
;; Requires the `consult' package.
(add-hook 'completion-list-mode-hook #'consult-preview-at-point-mode)

;;;; Setup for Orderless
;; Requires the `orderless' package

;; We make the SPC key insert a literal space and the same for the
;; question mark.  Spaces are used to delimit orderless groups, while
;; the quedtion mark is a valid regexp character.
(let ((map minibuffer-local-completion-map))
  (define-key map (kbd "SPC") nil)
  (define-key map (kbd "?") nil))

;; Because SPC works for Orderless and is trivial to activate, I like to
;; put `orderless' at the end of my `completion-styles'.  Like this:
(setq completion-styles
      '(basic substring initials flex partial-completion orderless))
(setq completion-category-overrides
      '((file (styles . (basic partial-completion orderless)))))

MCT defines its own keymaps, which extend those that are active in the minibuffer and the *Completions* buffer, respectively:

• mct-completion-list-mode-map
• mct-minibuffer-local-completion-map

You can invoke describe-keymap to learn more about them.

If you want to edit any key bindings, do it in these keymaps, not in those they extend and override (the names of the original ones are the same as above, minus the mct- prefix).

In this section we cover custom code that builds on what MCT offers.

MCT only tweaks the default minibuffer. To get more out of it, consider these exceptionally well-crafted extras:

Consult by Daniel Mendler

Adds several commands that make interacting with the minibuffer more powerful. There also are multiple packages that build on it, such as consult-dir by Karthik Chikmagalur and consult-notmuch by José Antonio Ortega Ruiz.

Embark by Omar Antolín Camarena

Provides configurable contextual actions for completions and many other constructs inside buffers. A genius package!

Marginalia by Daniel and Omar

Displays informative annotations for all known types of completion candidates.

Orderless by Omar

A completion style that matches a variety of patterns (regexp, flex, initialism, etc.) regardless of the order they appear in.

all-the-icons-completion by Itai Y. Efrat

Glue code that adds icons from the all-the-icons package to the *Completions* buffer. It can make things prettier and/or more informative, while it can also be combined with Marginalia.

MCT does not support the use-case of completion-in-region. This is the kind of completion session that is done inside the buffer and does not involve the minibuffer. However, you may prefer:

Corfu by Daniel Mendler

An interface for the completion-in-region which uses a child frame (basically a pop-up) at the position of the cursor to display candidates. As with all of Daniel’s packages, Corfu aims for a clean implementation that does the right thing by being consistent with core Emacs mechanisms.

Cape also by Daniel

Additional completion-at-point-functions (CAPFs) that extend those of core Emacs. These backends can be used by packages that visualise completion-in-region.

In the grand scheme of things, it may be helpful to think of MCT as proof-of-concept on how the default Emacs completion can become more expressive. MCT’s value rests in its potential to inspire developers to (i) patch Emacs so that its out-of-the-box completion is more interactive, and (ii) expose the shortcomings in the current implementation of the *Completions* buffer, which should again provide an impetus for further changes to Emacs. Otherwise, MCT is meant for users who can tolerate the status quo and simply want a thin layer of interactivity for minibuffer completion, in-buffer completion, and their intersection with the Completions’ buffer.

Like MCT, these alternatives provide a thin layer of functionality over the built-in infrastructure. Unlike MCT, they are not constrained by the design of the *Completions* buffer and concomitant functionality. They all make for a natural complement to the standard Emacs experience (also Extensions).

Vertico by Daniel Mendler

this is a more mature and feature-rich package with a large user base and a highly competent maintainer.

Vertico has some performance optimizations on how candidates are sorted and presented, which means that it displays results right away without any noticeable performance penalty. Whereas MCT does not change the underlying behaviour of how candidates are displayed. As such, MCT will be slower in scenaria where there are lots of candidates because core Emacs lacks those optimizations. One such case is with the describe-symbol (C-h o) prompt. If the user asks for the completions’ buffer without inputting any character (so without narrowing the list), there will be a noticeable delay before the buffer is rendered. This is mitigated in MCT by the requirement for mct-minimum-input, though the underlying mechanics remain intact.

In terms of the interaction model, the main difference between Vertico and MCT is that the former uses the minibuffer by default and shows the completions there. The minibuffer is expanded to show the candidates in a vertical list. Whereas MCT keeps the *Completions* buffer and the minibuffer as separate entities, the way standard Emacs does it.

The presence of a fully fledged buffer means that the user can invoke all relevant commands at their disposal, such as to write the buffer to a file for future review, use Isearch to move around, copy a string or rectangle to a register, and so on.

Vertico has official extensions which can make it work exactly like MCT without any of MCT’s drawbacks. These extensions can also expand Vertico’s powers such as by providing granular control over the exact style of presentation for any given completion category (e.g. display Imenu in a separate buffer, show the switch-to-buffer list horizontally in the minibuffer, and present find-file in a vertical list—whatever the user wants).

All things considered, there is no compelling reason why one may prefer MCT over Vertico in terms of the available functionality: Vertico is better.

Icomplete and fido-mode (built-in, multiple authors)

Icomplete is closer in spirit to Vertico, as it too uses the minibuffer to display completion candidates. By default, it presents the list horizontally, though there exists icomplete-vertical-mode (and fido-vertical-mode).

For our purposes, Icomplete and Fido are the same in terms of the paradigm they follow. The latter is a re-spin of the former, as it adjusts certain variables and binds some commands for the convenience of the end-user. fido-mode and its accoutrements are defined in icomplete.el.

What MCT borrows from Icomplete is for the input delay (explained elsewhere in this document). Internally, I also learnt how to extend local keymaps by studying icomplete.el.

I had used Icomplete for several months before moving to what now has become mct.el. I think it is excellent at providing a thin layer over the built-in infrastructure.

MCT is meant to be a collective effort. Every bit of help matters.

Author/maintainer

Protesilaos Stavrou.

Contributions to code or documentation

Daniel Mendler, James Norman Vladimir Cash, Jessie Hu, José Antonio Ortega Ruiz, Juri Linkov, Philip Kaludercic, Tomasz Hołubowicz.

Ideas and user feedback

Andrew Tropin, Benjamin (@zealotrush), Case Duckworth, Chris Burroughs, Jonathan Irving, José Antonio Ortega Ruiz, Kostadin Ninev, Manuel Uberti, Morgan Willcock, Philip Kaludercic, Theodor Thornhill, Tomasz Hołubowicz, Z.Du. As well as users: danrobi11.

Packaging

Andrew Tropin and Nicolas Goaziou (Guix).

Inspiration for certain features

icomplete.el (built-in—multiple authors), Daniel Mendler (vertico), Omar Antolín Camarena (embark, live-completions).

Manual

https://protesilaos.com/emacs/mct

Change log

https://protesilaos.com/emacs/mct-changelog

Source code

https://github.com/protesilaos/mct

Mailing list

https://lists.sr.ht/~protesilaos/mct

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10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the
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https://www.gnu.org/licenses/.

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"Massive Multiauthor Collaboration" (or "MMC") contained in the site
means any set of copyrightable works thus published on the MMC site.

"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.

"Incorporate" means to publish or republish a Document, in whole or in
part, as part of another Document.

An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole or
in part into the MMC, (1) had no cover texts or invariant sections, and
(2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.


ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

    Copyright (c)  YEAR  YOUR NAME.
    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
    A copy of the license is included in the section entitled "GNU
    Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.