#+TITLE: Orderless
#+AUTHOR: Omar Antolín Camarena
#+OPTIONS: d:nil
#+EXPORT_FILE_NAME: orderless.texi
#+TEXINFO_DIR_CATEGORY: Emacs misc features
#+TEXINFO_DIR_TITLE: Orderless: (orderless).
#+TEXINFO_DIR_DESC: Completion style for matching regexps in any order

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* Overview
:PROPERTIES:
:TOC: :include all :ignore this
:END:

This package provides an =orderless= /completion style/ that divides the
pattern into space-separated components, and matches candidates that
match all of the components in any order. Each component can match in
any one of several ways: literally, as a regexp, as an initialism, in
the flex style, or as multiple word prefixes. By default, regexp and
literal matches are enabled.

A completion style is a back-end for completion and is used from a
front-end that provides a completion UI. Any completion style can be
used with the default Emacs completion UI (sometimes called minibuffer
tab completion), with the built-in Icomplete package (which is similar
to the more well-known Ido Mode), the icomplete-vertical variant from
Emacs 28, or with minibuffer completion frameworks such as [[https://gitlab.com/protesilaos/mct][Mct]] or
[[https://github.com/minad/vertico][Vertico]].

All the completion UIs just mentioned are for minibuffer completion,
used when Emacs commands prompt the user in the minibuffer for some
input, but there is also completion at point in normal buffers,
typically used for identifiers in programming languages. Completion
styles can also be used for that purpose by completion at point UIs
such as [[https://github.com/minad/corfu][Corfu]], [[https://company-mode.github.io/][Company]] or the function =consult-completion-in-region=
from [[https://github.com/minad/consult][Consult]].

To use a completion style with any of the above mentioned completion
UIs simply add it as an entry in the variables =completion-styles= and
=completion-category-overrides= and =completion-category-defaults= (see
their documentation).

The =completion-category-defaults= variable serves as a default value
for =completion-category-overrides=. If you want to use =orderless=
exclusively, set both variables to =nil=, but be aware that
=completion-category-defaults= is modified by packages at load time.

With a bit of effort, it might still be possible to use =orderless= with
other completion UIs, even if those UIs don't support the standard
Emacs completion styles. Currently there is support for [[https://github.com/abo-abo/swiper][Ivy]], as
documented below. Also, while Company does support completion styles
directly, pressing =SPC= takes you out of completion, so comfortably
using =orderless= with it takes a bit of configuration (see below).

If you use ELPA or MELPA, the easiest way to install =orderless= is via
=package-install=. If you use =use-package=, you can use:

#+begin_src emacs-lisp
  (use-package orderless
    :ensure t
    :custom
    (completion-styles '(orderless basic))
    (completion-category-overrides '((file (styles partial-completion))))
    (completion-pcm-leading-wildcard t)) ;; Emacs 31: partial-completion behaves like substring
#+end_src

Alternatively, put =orderless.el= somewhere on your =load-path=, and use
the following configuration:

#+begin_src emacs-lisp
  (require 'orderless)
  (setq completion-styles '(orderless basic)
        completion-category-overrides '((file (styles partial-completion)))
        completion-pcm-leading-wildcard t) ;; Emacs 31: partial-completion behaves like substring
#+end_src

The =basic= completion style is specified as fallback in addition to
=orderless= in order to ensure that completion commands which rely on
dynamic completion tables, e.g., ~completion-table-dynamic~ or
~completion-table-in-turn~, work correctly. Furthermore the =basic=
completion style needs to be tried /first/ (not as a fallback) for TRAMP
hostname completion to work. In order to achieve that, we add an entry
for the =file= completion category in the =completion-category-overrides=
variable. In addition, the =partial-completion= style allows you to use
wildcards for file completion and partial paths, e.g., ~/u/s/l~ for
~/usr/share/local~.

Bug reports are highly welcome and appreciated!

:CONTENTS:
- [[#screenshot][Screenshot]]
- [[#customization][Customization]]
  - [[#component-matching-styles][Component matching styles]]
    - [[#style-dispatchers][Style dispatchers]]
  - [[#component-separator-regexp][Component separator regexp]]
  - [[#faces-for-component-matches][Faces for component matches]]
  - [[#pattern-compiler][Pattern compiler]]
  - [[#interactively-changing-the-configuration][Interactively changing the configuration]]
- [[#integration-with-other-completion-uis][Integration with other completion UIs]]
  - [[#ivy][Ivy]]
  - [[#company][Company]]
- [[#related-packages][Related packages]]
  - [[#ivy-and-helm][Ivy and Helm]]
  - [[#prescient][Prescient]]
  - [[#restricting-to-current-matches-in-icicles-ido-and-ivy][Restricting to current matches: Icicles, Ido and Ivy]]
:END:

** Screenshot :noexport:

This is what it looks like to use =describe-function= (bound by default
to =C-h f=) to match =eis ff=. Notice that in this particular case =eis=
matched as an initialism, and =ff= matched as a regexp. The completion
UI in the screenshot is icomplete-vertical and the theme is
Protesilaos Stavrou's lovely [[https://gitlab.com/protesilaos/modus-themes][modus-operandi]].

[[https://github.com/oantolin/orderless/blob/dispatcher/images/describe-function-eis-ff.png?raw=true]]

* Customization

** Component matching styles

Each component of a pattern can match in any of several matching
styles. A matching style is a function from strings to regexps or
predicates, so it is easy to define new matching styles. The value
returned by a matching style can be either a regexp as a string, an
s-expression in =rx= syntax or a predicate function. The predefined
matching styles are:

- orderless-regexp :: the component is treated as a regexp that must
  match somewhere in the candidate.

  If the component is not a valid regexp, it is ignored.

- orderless-literal :: the component is treated as a literal string
  that must occur in the candidate.

- orderless-literal-prefix :: the component is treated as a literal
  string that must occur as a prefix of a candidate.

- orderless-prefixes :: the component is split at word endings and
  each piece must match at a word boundary in the candidate, occurring
  in that order.

  This is similar to the built-in =partial-completion= completion-style.
  For example, =re-re= matches =query-replace-regexp=, =recode-region= and
  =magit-remote-list-refs=; =f-d.t= matches =final-draft.txt=.

- orderless-initialism :: each character of the component should appear
  as the beginning of a word in the candidate, in order.

  This maps =abc= to =\<a.*\<b.*\c=.

- orderless-flex :: the characters of the component should appear in
  that order in the candidate, but not necessarily consecutively.

  This maps =abc= to =a.*b.*c=.

- *orderless-without-literal* :: the component is a treated as a literal
  string that must *not* occur in the candidate.

  Nothing is highlighted by this style. This style should not be used
  directly in =orderless-matching-styles= but with a style dispatcher
  instead. See also the more general style modifier =orderless-not=.

The variable =orderless-matching-styles= can be set to a list of the
desired matching styles to use. By default it enables the literal and
regexp styles.

*** Style modifiers

Style modifiers are functions which take a predicate function and a
regular expression as a string and return a new predicate function.
Style modifiers should not be used directly in
=orderless-matching-styles= but with a style dispatcher instead.

- orderless-annotation :: this style modifier matches the pattern
  against the annotation string of the candidate, instead of against
  the candidate string.

- orderless-not :: this style modifier inverts the pattern, such that
  candidates pass which do not match the pattern.

*** Style dispatchers

 For more fine-grained control on which matching styles to use for
 each component of the input string, you can customize the variable
 =orderless-style-dispatchers=. You can use this feature to define your
 own "query syntax". For example, the default value of
 =orderless-style-dispatchers= lists a single dispatcher called
 =orderless-affix-dispatch= which enables a simple syntax based on
 special characters used as either a prefix or suffix:

 - ! modifies the component with =orderless-not=. Both =!bad= and
   =bad!= will match strings that do /not/ contain the pattern =bad=.
 - & modifies the component with =orderless-annotation=. The pattern
   will match against the candidate's annotation (cheesy mnemonic:
   andnotation!).
 - , uses =orderless-initialism=.
 - = uses =orderless-literal=.
 - ^ uses =orderless-literal-prefix=.
 - ~ uses =orderless-flex=.
 - % makes the string match ignoring diacritics and similar
   inflections on characters (it uses the function
   =char-fold-to-regexp= to do this).

 You can add, remove or change this mapping between affix characters
 and matching styles by customizing the user option
 =orderless-affix-dispatch-alist=. Most users will probably find this
 type of customization sufficient for their query syntax needs, but
 for those desiring further control the rest of this section explains
 how to implement your own style dispatchers.

 Style dispatchers are functions which take a component, its index in
 the list of components (starting from 0), and the total number of
 components, and are used to determine the matching styles used for
 that specific component, overriding the default matching styles.

 A style dispatcher can either decline to handle the input string or
 component, or it can return which matching styles to use. It can
 also, if desired, additionally return a new string to use in place of
 the given one. Consult the documentation of =orderless--dispatch= for
 full details.

 As an example of writing your own dispatchers, say you wanted the
 following setup:

 - you normally want components to match as regexps,
 - except for the first component, which should always match as an
   initialism ---this is pretty useful for, say,
   =execute-extended-command= (=M-x=) or =describe-function= (=C-h f=),
 - later components ending in =~= should match (the characters
   other than the final =~=) in the flex style, and
 - later components starting with =!= should indicate the rest of the
   component is a literal string not contained in the candidate (this
   is part of the functionality of the default configuration).

 You can achieve this with the following configuration:

 #+begin_src emacs-lisp
   (defun flex-if-twiddle (pattern _index _total)
     (when (string-suffix-p "~" pattern)
       `(orderless-flex . ,(substring pattern 0 -1))))

   (defun first-initialism (pattern index _total)
     (if (= index 0) 'orderless-initialism))

   (defun not-if-bang (pattern _index _total)
     (cond
      ((equal "!" pattern)
       #'ignore)
      ((string-prefix-p "!" pattern)
       `(orderless-not . ,(substring pattern 1)))))

   (setq orderless-matching-styles '(orderless-regexp)
         orderless-style-dispatchers '(first-initialism
                                       flex-if-twiddle
                                       not-if-bang))
 #+end_src

** Component separator regexp

The pattern components are space-separated by default: this is
controlled by the variable =orderless-component-separator=, which should
be set either to a regexp that matches the desired component
separator, or to a function that takes a string and returns the list
of components. The default value is a regexp matches a non-empty
sequence of spaces. It may be useful to add hyphens or slashes (or
both), to match symbols or file paths, respectively.

 Even if you want to split on spaces you might want to be able to
escape those spaces or to enclose space in double quotes (as in shell
argument parsing). For backslash-escaped spaces set
=orderless-component-separator= to the function
=orderless-escapable=; for shell-like double-quotable
space, set it to the standard Emacs function =split-string-and-unquote=.

If you are implementing a command for which you know you want a
different separator for the components, bind
=orderless-component-separator= in a =let= form.

** Defining custom orderless styles

Orderless allows the definition of custom completion styles using the
~orderless-define-completion-style~ macro. Any Orderless configuration
variable can be adjusted locally for the new style, e.g.,
~orderless-matching-styles~.

By default Orderless only enables the regexp and literal matching
styles. In the following example an ~orderless+initialism~ style is
defined, which additionally enables initialism matching. This completion
style can then used when matching candidates of the symbol or command
completion category.

#+begin_src emacs-lisp
  (orderless-define-completion-style orderless+initialism
    (orderless-matching-styles '(orderless-initialism
                                 orderless-literal
                                 orderless-regexp)))
  (setq completion-category-overrides
        '((command (styles orderless+initialism))
          (symbol (styles orderless+initialism))
          (variable (styles orderless+initialism))))
#+end_src

Note that in order for the =orderless+initialism= style to kick-in with
the above configuration, you'd need to use commands whose metadata
indicates that the completion candidates are commands or symbols. In
Emacs 28, =execute-extended-command= has metadata indicating you are
selecting a command, but earlier versions of Emacs lack this metadata.
Activating =marginalia-mode= from the [[https://github.com/minad/marginalia][Marginalia]] package provides this
metadata automatically for many built-in commands and is recommended
if you use the above example configuration, or other similarly
fine-grained control of completion styles according to completion
category.

** Faces for component matches

The portions of a candidate matching each component get highlighted in
one of four faces, =orderless-match-face-?= where =?= is a number from 0
to 3. If the pattern has more than four components, the faces get
reused cyclically.

If your =completion-styles= (or =completion-category-overrides= for some
particular category) has more than one entry, remember than Emacs
tries each completion style in turn and uses the first one returning
matches. You will only see these particular faces when the =orderless=
completion is the one that ends up being used, of course.

** Pattern compiler

The default mechanism for turning an input string into a predicate and a list of
regexps to match against, configured using =orderless-matching-styles=, is
probably flexible enough for the vast majority of users. The patterns are
compiled by =orderless-compile=. Under special circumstances it may be useful to
implement a custom pattern compiler by advising =orderless-compile=.

** Interactively changing the configuration

You might want to change the separator or the matching style
configuration on the fly while matching. There many possible user
interfaces for this: you could toggle between two chosen
configurations, cycle among several, have a keymap where each key sets
a different configurations, have a set of named configurations and be
prompted (with completion) for one of them, popup a [[https://github.com/abo-abo/hydra][hydra]] to choose a
configuration, etc. Since there are so many possible UIs and which to
use is mostly a matter of taste, =orderless= does not provide any such
commands. But it's easy to write your own!

For example, say you want to use the keybinding =C-l= to make all
components match literally. You could use the following code:

#+begin_src emacs-lisp
  (defun my/match-components-literally ()
    "Components match literally for the rest of the session."
    (interactive)
    (setq-local orderless-matching-styles '(orderless-literal)
                orderless-style-dispatchers nil))

  (define-key minibuffer-local-completion-map (kbd "C-l")
    #'my/match-components-literally)
#+end_src

Using =setq-local= to assign to the configuration variables ensures the
values are only used for that minibuffer completion session.

* Integration with other completion UIs

Several excellent completion UIs exist for Emacs in third party
packages. They do have a tendency to forsake standard Emacs APIs, so
integration with them must be done on a case by case basis.

If you manage to use =orderless= with a completion UI not listed here,
please file an issue or make a pull request so others can benefit from
your effort. The functions =orderless-filter=,
=orderless-highlight-matches=, =orderless--highlight= and
=orderless--component-regexps= are likely to help with the
integration.

** Ivy

To use =orderless= from Ivy add this to your Ivy configuration:

#+begin_src emacs-lisp
  (setq ivy-re-builders-alist '((t . orderless-ivy-re-builder)))
  (add-to-list 'ivy-highlight-functions-alist '(orderless-ivy-re-builder . orderless-ivy-highlight))
#+end_src

** Helm

To use =orderless= from Helm, simply configure =orderless= as you would
for completion UIs that use Emacs completion styles and add this to
your Helm configuration:

#+begin_src emacs-lisp
(setq helm-completion-style 'emacs)
#+end_src

** Company

Company comes with a =company-capf= backend that uses the
completion-at-point functions, which in turn use completion styles.
This means that the =company-capf= backend will automatically use
=orderless=, no configuration necessary!

But there are a couple of points of discomfort:

1. Pressing SPC takes you out of completion, so with the default
   separator you are limited to one component, which is no fun. To fix
   this add a separator that is allowed to occur in identifiers, for
   example, for Emacs Lisp code you could use an ampersand:

   #+begin_src emacs-lisp
     (setq orderless-component-separator "[ &]")
   #+end_src

2. The matching portions of candidates aren't highlighted. That's
   because =company-capf= is hard-coded to look for the
   =completions-common-part= face, and it only use one face,
   =company-echo-common= to highlight candidates.

   So, while you can't get different faces for different components,
   you can at least get the matches highlighted in the sole available
   face with this configuration:

   #+begin_src emacs-lisp
     (defun just-one-face (fn &rest args)
       (let ((orderless-match-faces [completions-common-part]))
         (apply fn args)))

     (advice-add 'company-capf--candidates :around #'just-one-face)
   #+end_src

   (Aren't dynamically scoped variables and the advice system nifty?)

If you would like to use different =completion-styles= with =company-capf= instead, you
can add this to your configuration:

#+begin_src emacs-lisp
  ;; We follow a suggestion by company maintainer u/hvis:
  ;; https://www.reddit.com/r/emacs/comments/nichkl/comment/gz1jr3s/
  (defun company-completion-styles (capf-fn &rest args)
    (let ((completion-styles '(basic partial-completion)))
      (apply capf-fn args))

  (advice-add 'company-capf :around #'company-completion-styles)
#+end_src

* Related packages

** Ivy and Helm

The well-known and hugely powerful completion frameworks [[https://github.com/abo-abo/swiper][Ivy]] and [[https://github.com/emacs-helm/helm][Helm]]
also provide for matching space-separated component regexps in any
order. In Ivy, this is done with the =ivy--regex-ignore-order= matcher.
In Helm, it is the default, called "multi pattern matching".

This package is significantly smaller than either of those because it
solely defines a completion style, meant to be used with any
completion UI supporting completion styles while both of those provide
their own completion UI (and many other cool features!).

It is worth pointing out that Helm does provide its multi pattern
matching as a completion style which could be used with default tab
completion, Icomplete or other UIs supporting completion styles! (Ivy
does not provide a completion style to my knowledge.) So, for example,
Icomplete users could, instead of using this package, install Helm and
configure Icomplete to use it as follows:

#+begin_src emacs-lisp
  (require 'helm)
  (setq completion-styles '(helm basic))
  (icomplete-mode)
#+end_src

(Of course, if you install Helm, you might as well use the Helm UI in
=helm-mode= rather than Icomplete.)

** Prescient

The [[https://github.com/radian-software/prescient.el][prescient.el]] library also provides matching of space-separated
components in any order. It offers a completion-style that can be used
with Emacs' default completion UI, Mct, Vertico or with Icomplete.
Furthermore Ivy is supported. The components can be matched literally,
as regexps, as initialisms or in the flex style (called "fuzzy" in
prescient). Prescient does not offer the same flexibility as Orderless
with its style dispatchers. However in addition to matching, Prescient
supports sorting of candidates, while Orderless leaves that up to the
candidate source and the completion UI.

** Restricting to current matches in Icicles, Ido and Ivy

An effect equivalent to matching multiple components in any order can
be achieved in completion frameworks that provide a way to restrict
further matching to the current list of candidates. If you use the
keybinding for restriction instead of =SPC= to separate your components,
you get out of order matching!

- [[https://www.emacswiki.org/emacs/Icicles][Icicles]] calls this /progressive completion/ and uses the
  =icicle-apropos-complete-and-narrow= command, bound to =S-SPC=, to do it.

- Ido has =ido-restrict-to-matches= and binds it to =C-SPC=.

- Ivy has =ivy-restrict-to-matches=, bound to =S-SPC=, so you can get the
  effect of out of order matching without using =ivy--regex-ignore-order=.
