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

:BADGES:
[[https://melpa.org/#/orderless][file:https://melpa.org/packages/orderless-badge.svg]]
[[https://stable.melpa.org/#/orderless][file:https://stable.melpa.org/packages/orderless-badge.svg]]
:END:

* 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), or with some third party completion
frameworks such as [[https://github.com/raxod502/selectrum][Selectrum]] or [[https://github.com/oantolin/icomplete-vertical][icomplete-vertical]]. To use a
completion style in this fashion simply add it as an entry in the
variables =completion-styles= and =completion-category-overrides= (see
their documentation). You may also want to modify the
=completion-category-defaults= variable, which serves as a default value
for =completion-category-overrides=: if you want to use =orderless=
exclusively, set both variables to =nil=.

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]] (see
below).

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

#+begin_src emacs-lisp
  (use-package orderless
    :ensure t
    :custom (completion-styles '(orderless)))
#+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))
#+end_src

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]]
  - [[#selectrum][Selectrum]]
  - [[#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 [[https://github.com/oantolin/icomplete-vertical][icomplete-vertical]] and the theme is
Protesilaos Stavrou's lovely [[https://gitlab.com/protesilaos/modus-themes][modus-operandi]].

[[images/describe-function-eis-ff.png]]

* Customization

** Component matching styles

Each component of a pattern can match in any of several matching
styles. A matching style is simply a function from strings to strings
that maps a component to a regexp to match against, so it is easy to
define new matching styles. The predefined ones 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.

  This is just =regexp-quote=.

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

  Note that nothing is highlighted for this matching style. You
  probably don't want to use this style directly in
  =orderless-matching-styles= but with a style dispatcher instead. There
  is an example in the section on style dispatchers.

- 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-strict-initialism :: like initialism but only allow
  non-letters in between the matched words.

  For example =fb= would match =foo-bar= but not =foo-qux-bar=.

- orderless-strict-leading-initialism :: like strict-initialism but
  require the first initial to match the candidate's first word.

  For example =bb= would match =bar-baz= but not =foo-bar-baz=.

- orderless-strict-full-initialism :: like strict-initialism but
  require the first initial to match the candidate's first word and the
  last initial to be at the final word.

  For example =fbb= would match =foo-bar-baz= but not =foo-bar-baz-qux=.

- 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=.

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 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=.

 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, 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.

 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 without-if-bang (pattern _index _total)
     (cond
      ((equal "!" pattern)
       '(orderless-literal . ""))
      ((string-prefix-p "!" pattern)
       `(orderless-without-literal . ,(substring pattern 1)))))

   (setq orderless-matching-styles '(orderless-regexp)
         orderless-style-dispatchers '(first-initialism
                                       flex-if-twiddle
                                       without-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-split-on-space=; 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))))
#+end_src

** 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 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 the
=orderless-pattern-compiler=. Under special circumstances it may be useful to
implement a custom pattern compiler by advising the
=orderless-pattern-compiler=.

** 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)))
#+end_src

** Selectrum

Recent versions of Selectrum default to using whatever completion
styles you have configured. You can use =orderless= that way, or you can
use this configuration:

#+begin_src emacs-lisp
  (setq selectrum-refine-candidates-function #'orderless-filter)
  (setq selectrum-highlight-candidates-function #'orderless-highlight-matches)
#+end_src

If you use the above configuration, only the visible candidates are
highlighted, which is a litte more efficient.

** 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?)

* 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, Selectrum 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))
  (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/raxod502/prescient.el][prescient.el]] library also provides matching of space-separated
components in any order and it can be used with either the [[https://github.com/raxod502/selectrum][Selectrum]]
or [[https://github.com/abo-abo/swiper][Ivy]] completion UIs (it does not offer a completion-style that
could be used with Emacs' default completion UI or with Icomplete).
The components can be matched literally, as regexps, as initialisms or
in the flex style (called "fuzzy" in prescient). In addition to
matching, =prescient.el= also supports sorting of candidates (=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=.