Transient User and Developer Manual
***********************************

Transient is the library used to implement the keyboard-driven ``menus'' in Magit.  It is distributed as a separate package, so that it can be used to implement similar menus in other packages.

This manual can be bit hard to digest when getting started.  A useful resource to get over that hurdle is Psionic K's interactive tutorial, available at https://github.com/positron-solutions/transient-showcase.

This manual is for Transient version 0.7.2.2.

     Copyright (C) 2018--2025 Free Software Foundation, Inc.

     You can redistribute this document and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

     This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

Introduction
************

Transient is the library used to implement the keyboard-driven menus in Magit.  It is distributed as a separate package, so that it can be used to implement similar menus in other packages.

This manual can be bit hard to digest when getting started.  A useful resource to get over that hurdle is Psionic K's interactive tutorial, available at https://github.com/positron-solutions/transient-showcase.

Some things that Transient can do
=================================

  * Display current state of arguments

  * Display and manage lifecycle of modal bindings

  * Contextual user interface

  * Flow control for wizard-like composition of interactive forms

  * History & persistence

  * Rendering arguments for controlling CLI programs

Complexity in CLI programs
==========================

Complexity tends to grow with time.  How do you manage the complexity of commands?  Consider the humble shell command ls.  It now has over fifty command line options.  Some of these are boolean flags (ls -l). Some take arguments (ls --sort=s).  Some have no effect unless paired with other flags (ls -lh).  Some are mutually exclusive.  Some shell commands even have so many options that they introduce subcommands (git branch, git commit), each with their own rich set of options (git branch -f).

Using Transient for composing interactive commands
==================================================

What about Emacs commands used interactively?  How do these handle options?  One solution is to make many versions of the same command, so you don't need to!  Consider: delete-other-windows vs. delete-other-windows-vertically (among many similar examples).

Some Emacs commands will simply prompt you for the next "argument" (M-x switch-to-buffer).  Another common solution is to use prefix arguments which usually start with C-u.  Sometimes these are sensibly numerical in nature (C-u 4 M-x forward-paragraph to move forward 4 paragraphs).  But sometimes they function instead as boolean "switches" (C-u C-SPACE to jump to the last mark instead of just setting it, C-u C-u C-SPACE to unconditionally set the mark).  Since there aren't many standards for the use of prefix options, you have to read the command's documentation to find out what the possibilities are.

But when an Emacs command grows to have a truly large set of options and arguments, with dependencies between them, lots of option values, etc., these simple approaches just don't scale.  Transient is designed to solve this issue.  Think of it as the humble prefix argument C-u, raised to the power of 10.  Like C-u, it is key driven.  Like the shell, it supports boolean "flag" options, options that take arguments, and even "sub-commands", with their own options.  But instead of searching through a man page or command documentation, well-designed transients guide their users to the relevant set of options (and even their possible values!) directly, taking into account any important pre-existing Emacs settings.  And while for shell commands like ls, there is only one way to "execute" (hit Return!), transients can "execute" using multiple different keys tied to one of many self-documenting actions (imagine having 5 different colored return keys on your keyboard!).  Transients make navigating and setting large, complex groups of command options and arguments easy.  Fun even.  Once you've tried it, it's hard to go back to the C-u what can I do here again? way.

Usage
*****

Invoking Transients
===================

A transient prefix command is invoked like any other command by pressing the key that is bound to that command.  The main difference to other commands is that a transient prefix command activates a transient keymap, which temporarily binds the transient's infix and suffix commands.  Bindings from other keymaps may, or may not, be disabled while the transient state is in effect.

There are two kinds of commands that are available after invoking a transient prefix command; infix and suffix commands.  Infix commands set some value (which is then shown in a popup buffer), without leaving the transient.  Suffix commands, on the other hand, usually quit the transient and they may use the values set by the infix commands, i.e., the infix arguments.

Instead of setting arguments to be used by a suffix command, infix commands may also set some value by side-effect, e.g., by setting the value of some variable.

Aborting and Resuming Transients
================================

To quit the transient without invoking a suffix command press C-g.

Key bindings in transient keymaps may be longer than a single event. After pressing a valid prefix key, all commands whose bindings do not begin with that prefix key are temporarily unavailable and grayed out. To abort the prefix key press C-g (which in this case only quits the prefix key, but not the complete transient).

A transient prefix command can be bound as a suffix of another transient.  Invoking such a suffix replaces the current transient state with a new transient state, i.e., the available bindings change and the information displayed in the popup buffer is updated accordingly.  Pressing C-g while a nested transient is active only quits the innermost transient, causing a return to the previous transient.

C-q or C-z on the other hand always exits all transients.  If you use the latter, then you can later resume the stack of transients using M-x transient-resume.

C-g (transient-quit-seq)
C-g (transient-quit-one)
     This key quits the currently active incomplete key sequence, if any, or else the current transient.  When quitting the current transient, it returns to the previous transient, if any.

Transient's predecessor bound q instead of C-g to the quit command. To learn how to get that binding back see transient-bind-q-to-quit's documentation string.

C-q (transient-quit-all)
     This command quits the currently active incomplete key sequence, if any, and all transients, including the active transient and all suspended transients, if any.

C-z (transient-suspend)
     Like transient-quit-all, this command quits an incomplete key sequence, if any, and all transients.  Additionally, it saves the stack of transients so that it can easily be resumed (which is particularly useful if you quickly need to do ``something else'' and the stack is deeper than a single transient, and/or you have already changed the values of some infix arguments).

     Note that only a single stack of transients can be saved at a time. If another stack is already saved, then saving a new stack discards the previous stack.

M-x transient-resume
     This command resumes the previously suspended stack of transients, if any.

Common Suffix Commands
======================

A few shared suffix commands are available in all transients.  These suffix commands are not shown in the popup buffer by default.

This includes the aborting commands mentioned in the previous section, as well as some other commands that are all bound to C-x KEY.  After C-x is pressed, a section featuring all these common commands is temporarily shown in the popup buffer.  After invoking one of them, the section disappears again.  Note, however, that one of these commands is described as ``Show common permanently''; invoke that if you want the common commands to always be shown for all transients.

C-x t (transient-toggle-common)
     This command toggles whether the generic commands that are common to all transients are always displayed or only after typing the incomplete prefix key sequence C-x.  This only affects the current Emacs session.

 -- User Option: transient-show-common-commands
     This option controls whether shared suffix commands are shown alongside the transient-specific infix and suffix commands.  By default, the shared commands are not shown to avoid overwhelming the user with too many options.

     While a transient is active, pressing C-x always shows the common commands.  The value of this option can be changed for the current Emacs session by typing C-x t while a transient is active.

The other common commands are described in either the previous or in one of the following sections.

Some of Transient's key bindings differ from the respective bindings of Magit-Popup; see FAQ for more information.

Saving Values
=============

After setting the infix arguments in a transient, the user can save those arguments for future invocations.

Most transients will start out with the saved arguments when they are invoked.  There are a few exceptions, though.  Some transients are designed so that the value that they use is stored externally as the buffer-local value of some variable.  Invoking such a transient again uses the buffer-local value.  (magit-diff and magit-log are two prominent examples, and their handling of buffer-local values is actually a bit more complicated than outlined above and even customizable.)

If the user does not save the value and just exits using a regular suffix command, then the value is merely saved to the transient's history.  That value won't be used when the transient is next invoked, but it is easily accessible (see Using History).

C-x s (transient-set)
     This command saves the value of the active transient for this Emacs session.

C-x C-s (transient-save)
     Save the value of the active transient persistently across Emacs sessions.

C-x C-k (transient-reset)
     Clear the set and saved values of the active transient.

 -- User Option: transient-values-file
     This option names the file that is used to persist the values of transients between Emacs sessions.

Using History
=============

Every time the user invokes a suffix command the transient's current value is saved to its history.  These values can be cycled through the same way one can cycle through the history of commands that read user-input in the minibuffer.

C-M-p (transient-history-prev)
C-x p
     This command switches to the previous value used for the active transient.

C-M-n (transient-history-next)
C-x n
     This command switches to the next value used for the active transient.

In addition to the transient-wide history, Transient of course supports per-infix history.  When an infix reads user-input using the minibuffer, the user can use the regular minibuffer history commands to cycle through previously used values.  Usually the same keys as those mentioned above are bound to those commands.

Authors of transients should arrange for different infix commands that read the same kind of value to also use the same history key (see Suffix Slots).

Both kinds of history are saved to a file when Emacs is exited.

 -- User Option: transient-history-file
     This option names the file that is used to persist the history of transients and their infixes between Emacs sessions.

 -- User Option: transient-history-limit
     This option controls how many history elements are kept at the time the history is saved in transient-history-file.

Getting Help for Suffix Commands
================================

Transients can have many suffixes and infixes that the user might not be familiar with.  To make it trivial to get help for these, Transient provides access to the documentation directly from the active transient.

C-h (transient-help)
     This command enters help mode.  When help mode is active, typing a key shows information about the suffix command that the key normally is bound to (instead of invoking it).  Pressing C-h a second time shows information about the prefix command.

     After typing a key, the stack of transient states is suspended and information about the suffix command is shown instead.  Typing q in the help buffer buries that buffer and resumes the transient state.

What sort of documentation is shown depends on how the transient was defined.  For infix commands that represent command-line arguments this ideally shows the appropriate manpage.  transient-help then tries to jump to the correct location within that.  Info manuals are also supported.  The fallback is to show the command's documentation string, for non-infix suffixes this is usually appropriate.

Enabling and Disabling Suffixes
===============================

The user base of a package that uses transients can be very diverse. This is certainly the case for Magit; some users have been using it and Git for a decade, while others are just getting started now.

For that reason a mechanism is needed that authors can use to classify a transient's infixes and suffixes along the essentials...everything spectrum.  We use the term levels to describe that mechanism.

Each suffix command is placed on a level and each transient has a level (called transient-level), which controls which suffix commands are available.  Integers between 1 and 7 (inclusive) are valid levels. For suffixes, 0 is also valid; it means that the suffix is not displayed at any level.

The levels of individual transients and/or their individual suffixes can be changed interactively, by invoking the transient and then pressing C-x l to enter the ``edit'' mode, see below.

The default level for both transients and their suffixes is 4.  The transient-default-level option only controls the default for transients.  The default suffix level is always 4.  The authors of transients should place certain suffixes on a higher level, if they expect that it won't be of use to most users, and they should place very important suffixes on a lower level, so that they remain available even if the user lowers the transient level.

 -- User Option: transient-default-level
     This option controls which suffix levels are made available by default.  It sets the transient-level for transients for which the user has not set that individually.

 -- User Option: transient-levels-file
     This option names the file that is used to persist the levels of transients and their suffixes between Emacs sessions.

C-x l (transient-set-level)
     This command enters edit mode.  When edit mode is active, then all infixes and suffixes that are currently usable are displayed along with their levels.  The colors of the levels indicate whether they are enabled or not.  The level of the transient is also displayed along with some usage information.

     In edit mode, pressing the key that would usually invoke a certain suffix instead prompts the user for the level that suffix should be placed on.

     Help mode is available in edit mode.

     To change the transient level press C-x l again.

     To exit edit mode press C-g.

     Note that edit mode does not display any suffixes that are not currently usable.  magit-rebase, for example, shows different suffixes depending on whether a rebase is already in progress or not.  The predicates also apply in edit mode.

     Therefore, to control which suffixes are available given a certain state, you have to make sure that that state is currently active.

C-x a (transient-toggle-level-limit)
     This command toggle whether suffixes that are on levels higher than the level specified by transient-default-level are temporarily available anyway.

Other Commands
==============

When invoking a transient in a small frame, the transient window may not show the complete buffer, making it necessary to scroll, using the following commands.  These commands are never shown in the transient window, and the key bindings are the same as for scroll-up-command and scroll-down-command in other buffers.

 -- Command: transient-scroll-up arg
     This command scrolls text of transient popup window upward ARG lines.  If ARG is nil, then it scrolls near full screen.  This is a wrapper around scroll-up-command (which see).

 -- Command: transient-scroll-down arg
     This command scrolls text of transient popup window down ARG lines.  If ARG is nil, then it scrolls near full screen.  This is a wrapper around scroll-down-command (which see).

Configuration
=============

More options are described in Common Suffix Commands, in Saving Values, in Using History and in Enabling and Disabling Suffixes.

Essential Options
-----------------

Also see Common Suffix Commands.

 -- User Option: transient-show-popup
     This option controls whether the current transient's infix and suffix commands are shown in the popup buffer.

       * If t (the default) then the popup buffer is shown as soon as a transient prefix command is invoked.

       * If nil, then the popup buffer is not shown unless the user explicitly requests it, by pressing an incomplete prefix key sequence.

       * If a number, then the a brief one-line summary is shown instead of the popup buffer.  If zero or negative, then not even that summary is shown; only the pressed key itself is shown.

          The popup is shown when the user explicitly requests it by pressing an incomplete prefix key sequence.  Unless this is zero, the popup is shown after that many seconds of inactivity (using the absolute value).

 -- User Option: transient-enable-popup-navigation
     This option controls whether navigation commands are enabled in the transient popup buffer.

     While a transient is active the transient popup buffer is not the current buffer, making it necessary to use dedicated commands to act on that buffer itself.  This is disabled by default.  If this option is non-nil, then the following features are available:

       * UP moves the cursor to the previous suffix.

       * DOWN moves the cursor to the next suffix.

       * RET invokes the suffix the cursor is on.

       * mouse-1 invokes the clicked on suffix.

       * C-s and C-r start isearch in the popup buffer.

 -- User Option: transient-display-buffer-action
     This option specifies the action used to display the transient popup buffer.  The transient popup buffer is displayed in a window using (display-buffer BUFFER transient-display-buffer-action).

     The value of this option has the form (FUNCTION . ALIST), where FUNCTION is a function or a list of functions.  Each such function should accept two arguments: a buffer to display and an alist of the same form as ALIST.  See Choosing Window (elisp), for details.

     The default is:

          (display-buffer-in-side-window
            (side . bottom)
            (inhibit-same-window . t)
            (window-parameters (no-other-window . t)))

     This displays the window at the bottom of the selected frame. Another useful FUNCTION is display-buffer-below-selected, which is what magit-popup used by default.  For more alternatives see Buffer Display Action Functions (elisp), and see Buffer Display Action Alists (elisp).

     Note that the buffer that was current before the transient buffer is shown should remain the current buffer.  Many suffix commands act on the thing at point, if appropriate, and if the transient buffer became the current buffer, then that would change what is at point.  To that effect inhibit-same-window ensures that the selected window is not used to show the transient buffer.

     It may be possible to display the window in another frame, but whether that works in practice depends on the window-manager. If the window manager selects the new window (Emacs frame), then that unfortunately changes which buffer is current.

     If you change the value of this option, then you might also want to change the value of transient-mode-line-format.

Accessibility Options
---------------------

 -- User Option: transient-force-single-column
     This option controls whether the use of a single column to display suffixes is enforced.  This might be useful for users with low vision who use large text and might otherwise have to scroll in two dimensions.

Auxiliary Options
-----------------

 -- User Option: transient-mode-line-format
     This option controls whether the transient popup buffer has a mode-line, separator line, or neither.

     If nil, then the buffer has no mode-line.  If the buffer is not displayed right above the echo area, then this probably is not a good value.

     If line (the default) or a natural number, then the buffer has no mode-line, but a line is drawn is drawn in its place. If a number is used, that specifies the thickness of the line. On termcap frames we cannot draw lines, so there line and numbers are synonyms for nil.

     The color of the line is used to indicate if non-suffixes are allowed and whether they exit the transient.  The foreground color of transient-key-noop (if non-suffix are disallowed), transient-key-stay (if allowed and transient stays active), or transient-key-exit (if allowed and they exit the transient) is used to draw the line.

     Otherwise this can be any mode-line format.  See Mode Line Format (elisp), for details.

 -- User Option: transient-semantic-coloring
     This option controls whether colors are used to indicate the transient behavior of commands.

     If non-nil, then the key binding of each suffix is colorized to indicate whether it exits the transient state or not.  The color of the prefix is indicated using the line that is drawn when the value of transient-mode-line-format is line.

 -- User Option: transient-highlight-mismatched-keys
     This option controls whether key bindings of infix commands that do not match the respective command-line argument should be highlighted. For other infix commands this option has no effect.

     When this option is non-nil, the key binding for an infix argument is highlighted when only a long argument (e.g., --verbose) is specified but no shorthand (e.g., -v).  In the rare case that a shorthand is specified but the key binding does not match, then it is highlighted differently.

     Highlighting mismatched key bindings is useful when learning the arguments of the underlying command-line tool; you wouldn't want to learn any short-hands that do not actually exist.

     The highlighting is done using one of the faces transient-mismatched-key and transient-nonstandard-key.

 -- User Option: transient-substitute-key-function
     This function is used to modify key bindings.  If the value of this option is nil (the default), then no substitution is performed.

     This function is called with one argument, the prefix object, and must return a key binding description, either the existing key description it finds in the key slot, or the key description that replaces the prefix key.  It could be used to make other substitutions, but that is discouraged.

     For example, = is hard to reach using my custom keyboard layout, so I substitute ( for that, which is easy to reach using a layout optimized for lisp.

          (setq transient-substitute-key-function
                (lambda (obj)
                  (let ((key (oref obj key)))
                    (if (string-match "\\`\\(=\\)[a-zA-Z]" key)
                        (replace-match "(" t t key 1)
                      key))))

 -- User Option: transient-read-with-initial-input
     This option controls whether the last history element is used as the initial minibuffer input when reading the value of an infix argument from the user.  If nil, there is no initial input and the first element has to be accessed the same way as the older elements.

 -- User Option: transient-hide-during-minibuffer-read
     This option controls whether the transient buffer is hidden while user input is being read in the minibuffer.

 -- User Option: transient-align-variable-pitch
     This option controls whether columns are aligned pixel-wise in the popup buffer.

     If this is non-nil, then columns are aligned pixel-wise to support variable-pitch fonts.  Keys are not aligned, so you should use a fixed-pitch font for the transient-key face.  Other key faces inherit from that face unless a theme is used that breaks that relationship.

     This option is intended for users who use a variable-pitch font for the default face.

 -- User Option: transient-force-fixed-pitch
     This option controls whether to force the use of a monospaced font in popup buffer.  Even if you use a proportional font for the default face, you might still want to use a monospaced font in transient's popup buffer.  Setting this option to t causes default to be remapped to fixed-pitch in that buffer.

Developer Options
-----------------

These options are mainly intended for developers.

 -- User Option: transient-detect-key-conflicts
     This option controls whether key binding conflicts should be detected at the time the transient is invoked.  If so, this results in an error, which prevents the transient from being used.  Because of that, conflicts are ignored by default.

     Conflicts cannot be determined earlier, i.e., when the transient is being defined and when new suffixes are being added, because at that time there can be false-positives.  It is actually valid for multiple suffixes to share a common key binding, provided the predicates of those suffixes prevent that more than one of them is enabled at a time.

 -- User Option: transient-highlight-higher-levels
     This option controls whether suffixes that would not be available by default are highlighted.

     When non-nil then the descriptions of suffixes are highlighted if their level is above 4, the default of transient-default-level. Assuming you have set that variable to 7, this highlights all suffixes that won't be available to users without them making the same customization.

Modifying Existing Transients
*****************************

To an extent, transients can be customized interactively, see Enabling and Disabling Suffixes.  This section explains how existing transients can be further modified non-interactively.  Let's begin with an example:

     (transient-append-suffix 'magit-patch-apply "-3"
       '("-R" "Apply in reverse" "--reverse"))

This inserts a new infix argument to toggle the --reverse argument after the infix argument that toggles -3 in magit-patch-apply.

The following functions share a few arguments:

  * PREFIX is a transient prefix command, a symbol.

  * SUFFIX is a transient infix or suffix specification in the same form as expected by transient-define-prefix.  Note that an infix is a special kind of suffix.  Depending on context ``suffixes'' means ``suffixes (including infixes)'' or ``non-infix suffixes''.  Here it means the former.  See Suffix Specifications.

     SUFFIX may also be a group in the same form as expected by transient-define-prefix.  See Group Specifications.

  * LOC is a command, a key vector, a key description (a string as returned by key-description), or a list specifying coordinates (the last element may also be a command or key).  For example (1 0 -1) identifies the last suffix (-1) of the first subgroup (0) of the second group (1).

     If LOC is a list of coordinates, then it can be used to identify a group, not just an individual suffix command.

     The function transient-get-suffix can be useful to determine whether a certain coordination list identifies the suffix or group that you expect it to identify.  In hairy cases it may be necessary to look at the definition of the transient prefix command.

These functions operate on the information stored in the transient--layout property of the PREFIX symbol.  Suffix entries in that tree are not objects but have the form (LEVEL CLASS PLIST), where PLIST should set at least :key, :description and :command.

 -- Function: transient-insert-suffix prefix loc suffix &optional keep-other

 -- Function: transient-append-suffix prefix loc suffix &optional keep-other
     These functions insert the suffix or group SUFFIX into PREFIX before or after LOC.

     Conceptually adding a binding to a transient prefix is similar to adding a binding to a keymap, but this is complicated by the fact that multiple suffix commands can be bound to the same key, provided they are never active at the same time, see Predicate Slots.

     Unfortunately both false-positives and false-negatives are possible. To deal with the former use non-nil KEEP-OTHER.  To deal with the latter remove the conflicting binding explicitly.

 -- Function: transient-replace-suffix prefix loc suffix
     This function replaces the suffix or group at LOC in PREFIX with suffix or group SUFFIX.

 -- Function: transient-remove-suffix prefix loc
     This function removes the suffix or group at LOC in PREFIX.

 -- Function: transient-get-suffix prefix loc
     This function returns the suffix or group at LOC in PREFIX.  The returned value has the form mentioned above.

 -- Function: transient-suffix-put prefix loc prop value
     This function edits the suffix or group at LOC in PREFIX, by setting the PROP of its plist to VALUE.

Most of these functions do not signal an error if they cannot perform the requested modification.  The functions that insert new suffixes show a warning if LOC cannot be found in PREFIX without signaling an error.  The reason for doing it like this is that establishing a key binding (and that is what we essentially are trying to do here) should not prevent the rest of the configuration from loading.  Among these functions only transient-get-suffix and transient-suffix-put may signal an error.

Defining New Commands
*********************

Technical Introduction
======================

Taking inspiration from prefix keys and prefix arguments, Transient implements a similar abstraction involving a prefix command, infix arguments and suffix commands.

When the user calls a transient prefix command, a transient (temporary) keymap is activated, which binds the transient's infix and suffix commands, and functions that control the transient state are added to pre-command-hook and post-command-hook.  The available suffix and infix commands and their state are shown in a popup buffer until the transient state is exited by invoking a suffix command.

Calling an infix command causes its value to be changed.  How that is done depends on the type of the infix command.  The simplest case is an infix command that represents a command-line argument that does not take a value.  Invoking such an infix command causes the switch to be toggled on or off.  More complex infix commands may read a value from the user, using the minibuffer.

Calling a suffix command usually causes the transient to be exited; the transient keymaps and hook functions are removed, the popup buffer no longer shows information about the (no longer bound) suffix commands, the values of some public global variables are set, while some internal global variables are unset, and finally the command is actually called.  Suffix commands can also be configured to not exit the transient.

A suffix command can, but does not have to, use the infix arguments in much the same way any command can choose to use or ignore the prefix arguments.  For a suffix command that was invoked from a transient, the variable transient-current-suffixes and the function transient-args serve about the same purpose as the variables prefix-arg and current-prefix-arg do for any command that was called after the prefix arguments have been set using a command such as universal-argument.

Transient can be used to implement simple ``command dispatchers''.  The main benefit then is that the user can see all the available commands in a popup buffer, which can be thought of as a ``menus''.  That is useful by itself because it frees the user from having to remember all the keys that are valid after a certain prefix key or command. Magit's magit-dispatch (on C-x M-g) command is an example of using Transient to merely implement a command dispatcher.

In addition to that, Transient also allows users to interactively pass arguments to commands.  These arguments can be much more complex than what is reasonable when using prefix arguments.  There is a limit to how many aspects of a command can be controlled using prefix arguments.  Furthermore, what a certain prefix argument means for different commands can be completely different, and users have to read documentation to learn and then commit to memory what a certain prefix argument means to a certain command.

Transient suffix commands, on the other hand, can accept dozens of different arguments without the user having to remember anything. When using Transient, one can call a command with arguments that are just as complex as when calling the same function non-interactively from Lisp.

Invoking a transient suffix command with arguments is similar to invoking a command in a shell with command-line completion and history enabled.  One benefit of the Transient interface is that it remembers history not only on a global level (``this command was invoked using these arguments, and previously it was invoked using those other arguments''), but also remembers the values of individual arguments independently.  See Using History.

After a transient prefix command is invoked, C-h KEY can be used to show the documentation for the infix or suffix command that KEY is bound to (see Getting Help for Suffix Commands), and infixes and suffixes can be removed from the transient using C-x l KEY.  Infixes and suffixes that are disabled by default can be enabled the same way. See Enabling and Disabling Suffixes.

Transient ships with support for a few different types of specialized infix commands.  A command that sets a command line option, for example, has different needs than a command that merely toggles a boolean flag. Additionally, Transient provides abstractions for defining new types, which the author of Transient did not anticipate (or didn't get around to implementing yet).

Note that suffix commands also support regular prefix arguments.  A suffix command may even be called with both infix and prefix arguments at the same time.  If you invoke a command as a suffix of a transient prefix command, but also want to pass prefix arguments to it, then first invoke the prefix command, and only after doing that invoke the prefix arguments, before finally invoking the suffix command.  If you instead began by providing the prefix arguments, then those would apply to the prefix command, not the suffix command.  Likewise, if you want to change infix arguments before invoking a suffix command with prefix arguments, then change the infix arguments before invoking the prefix arguments.  In other words, regular prefix arguments always apply to the next command, and since transient prefix, infix and suffix commands are just regular commands, the same applies to them. (Regular prefix keys behave differently because they are not commands at all, instead they are just incomplete key sequences, and those cannot be interrupted with prefix commands.)

Defining Transients
===================

A transient consists of a prefix command and at least one suffix command, though usually a transient has several infix and suffix commands.  The below macro defines the transient prefix command and binds the transient's infix and suffix commands.  In other words, it defines the complete transient, not just the transient prefix command that is used to invoke that transient.

 -- Macro: transient-define-prefix name arglist [docstring] [keyword value]... group... [body...]
     This macro defines NAME as a transient prefix command and binds the transient's infix and suffix commands.

     ARGLIST are the arguments that the prefix command takes. DOCSTRING is the documentation string and is optional.

     These arguments can optionally be followed by keyword-value pairs. Each key has to be a keyword symbol, either :class or a keyword argument supported by the constructor of that class.  The transient-prefix class is used if the class is not specified explicitly.

     GROUPs add key bindings for infix and suffix commands and specify how these bindings are presented in the popup buffer.  At least one GROUP has to be specified.  See Binding Suffix and Infix Commands.

     The BODY is optional.  If it is omitted, then ARGLIST is ignored and the function definition becomes:

          (lambda ()
            (interactive)
            (transient-setup 'NAME))

     If BODY is specified, then it must begin with an interactive form that matches ARGLIST, and it must call transient-setup.  It may, however, call that function only when some condition is satisfied.

     All transients have a (possibly nil) value, which is exported when suffix commands are called, so that they can consume that value. For some transients it might be necessary to have a sort of secondary value, called a ``scope''.  Such a scope would usually be set in the command's interactive form and has to be passed to the setup function:

          (transient-setup 'NAME nil nil :scope SCOPE)

     For example, the scope of the magit-branch-configure transient is the branch whose variables are being configured.

Binding Suffix and Infix Commands
=================================

The macro transient-define-prefix is used to define a transient. This defines the actual transient prefix command (see Defining Transients) and adds the transient's infix and suffix bindings, as described below.

Users and third-party packages can add additional bindings using functions such as transient-insert-suffix (see Modifying Existing Transients). These functions take a ``suffix specification'' as one of their arguments, which has the same form as the specifications used in transient-define-prefix.

Group Specifications
--------------------

The suffix and infix commands of a transient are organized in groups. The grouping controls how the descriptions of the suffixes are outlined visually but also makes it possible to set certain properties for a set of suffixes.

Several group classes exist, some of which organize suffixes in subgroups.  In most cases the class does not have to be specified explicitly, but see Group Classes.

Groups are specified in the call to transient-define-prefix, using vectors.  Because groups are represented using vectors, we cannot use square brackets to indicate an optional element and instead use curly brackets to do the latter.

Group specifications then have this form:

     [{LEVEL} {DESCRIPTION}
      {KEYWORD VALUE}...
      ELEMENT...]

The LEVEL is optional and defaults to 4.  See Enabling and Disabling Suffixes.

The DESCRIPTION is optional.  If present, it is used as the heading of the group.

The KEYWORD-VALUE pairs are optional.  Each keyword has to be a keyword symbol, either :class or a keyword argument supported by the constructor of that class.

  * One of these keywords, :description, is equivalent to specifying DESCRIPTION at the very beginning of the vector.  The recommendation is to use :description if some other keyword is also used, for consistency, or DESCRIPTION otherwise, because it looks better.

  * Likewise :level is equivalent to LEVEL.

  * Other important keywords include the :if... keywords.  These keywords control whether the group is available in a certain situation.

     For example, one group of the magit-rebase transient uses :if magit-rebase-in-progress-p, which contains the suffixes that are useful while rebase is already in progress; and another that uses :if-not magit-rebase-in-progress-p, which contains the suffixes that initiate a rebase.

     These predicates can also be used on individual suffixes and are only documented once, see Predicate Slots.

  * The value of :hide, if non-nil, is a predicate that controls whether the group is hidden by default.  The key bindings for suffixes of a hidden group should all use the same prefix key. Pressing that prefix key should temporarily show the group and its suffixes, which assumes that a predicate like this is used:

          (lambda ()
            (eq (car transient--redisplay-key)
                ?\C-c)) ; the prefix key shared by all bindings

  * The value of :setup-children, if non-nil, is a function that takes one argument, a potentially list of children, and must return a list of children or an empty list.  This can either be used to somehow transform the group's children that were defined the normal way, or to dynamically create the children from scratch.

     The returned children must have the same form as stored in the prefix's transient--layout property, but it is often more convenient to use the same form as understood by transient-define-prefix, described below.  If you use the latter approach, you can use the transient-parse-suffixes and transient-parse-suffix functions to transform them from the convenient to the expected form.  Depending on the used group class, transient-parse-suffixes's SUFFIXES must be a list of group vectors (for transient-columns) or a list of suffix lists (for all other group classes).

     If you explicitly specify children and then transform them using :setup-children, then the class of the group is determined as usual, based on explicitly specified children.

     If you do not explicitly specify children and thus rely solely on :setup-children, then you must specify the class using :class. For backward compatibility, if you fail to do so, transient-column is used and a warning is displayed.  This warning will eventually be replaced with an error.

          (transient-define-prefix my-finder-by-keyword ()
            "Select a keyword and list matching packages."
            ;; The real `finder-by-keyword' is more convenient
            ;; of course, but that is not the point here.
            [:class transient-columns
             :setup-children
             (lambda (_)
               (transient-parse-suffixes
                'my-finder-by-keyword
                (let ((char (1- ?A)))
                  (mapcar                  ; a list ...
                   (lambda (partition)
                     (vconcat              ; of group vectors ...
                      (mapcar (lambda (elt)
                                (let ((keyword (symbol-name (car elt))))
                                           ; ... where each suffix is a list
                                  (list (format "%c" (cl-incf char))
                                        keyword
                                        (lambda ()
                                          (interactive)
                                          (finder-list-matches keyword)))))
                              partition)))
                   (seq-partition finder-known-keywords 7)))))])

  * The boolean :pad-keys argument controls whether keys of all suffixes contained in a group are right padded, effectively aligning the descriptions.

The ELEMENTs are either all subgroups, or all suffixes and strings. (At least currently no group type exists that would allow mixing subgroups with commands at the same level, though in principle there is nothing that prevents that.)

If the ELEMENTs are not subgroups, then they can be a mixture of lists, which specify commands, and strings.  Strings are inserted verbatim into the buffer.  The empty string can be used to insert gaps between suffixes, which is particularly useful if the suffixes are outlined as a table.

Inside group specifications, including inside contained suffix specifications, nothing has to be quoted and quoting anyway is invalid.  The value following a keyword, can be explicitly unquoted using ,.  This feature is experimental and should be avoided.

The form of suffix specifications is documented in the next node.

Suffix Specifications
---------------------

A transient's suffix and infix commands are bound when the transient prefix command is defined using transient-define-prefix, see Defining Transients.  The commands are organized into groups, see Group Specifications.  Here we describe the form used to bind an individual suffix command.

The same form is also used when later binding additional commands using functions such as transient-insert-suffix, see Modifying Existing Transients.

Note that an infix is a special kind of suffix.  Depending on context ``suffixes'' means ``suffixes (including infixes)'' or ``non-infix suffixes''.  Here it means the former.

Suffix specifications have this form:

     ([LEVEL]
      [KEY [DESCRIPTION]]
      COMMAND|ARGUMENT [KEYWORD VALUE]...)

LEVEL, KEY and DESCRIPTION can also be specified using the KEYWORDs :level, :key and :description.  If the object that is associated with COMMAND sets these properties, then they do not have to be specified here.  You can however specify them here anyway, possibly overriding the object's values just for the binding inside this transient.

  * LEVEL is the suffix level, an integer between 1 and 7. See Enabling and Disabling Suffixes.

  * KEY is the key binding, either a vector or key description string.

  * DESCRIPTION is the description, either a string or a function that takes zero or one arguments (the suffix object) and returns a string. The function should be a lambda expression to avoid ambiguity.  In some cases a symbol that is bound as a function would also work but to be safe you should use :description in that case.

The next element is either a command or an argument.  This is the only argument that is mandatory in all cases.

  * COMMAND should be a symbol that is bound as a function, which has to be defined or at least autoloaded as a command by the time the containing prefix command is invoked.

     Any command will do; it does not need to have an object associated with it (as would be the case if transient-define-suffix or transient-define-infix were used to define it).

     COMMAND can also be a lambda expression.

     As mentioned above, the object that is associated with a command can be used to set the default for certain values that otherwise have to be set in the suffix specification.  Therefore if there is no object, then you have to make sure to specify the KEY and the DESCRIPTION.

     As a special case, if you want to add a command that might be neither defined nor autoloaded, you can use a workaround like:

          (transient-insert-suffix 'some-prefix "k"
            '("!" "Ceci n'est pas une commande" no-command
              :if (lambda () (featurep 'no-library))))

     Instead of featurep you could also use require with a non-nil value for NOERROR.

  * The mandatory argument can also be a command-line argument, a string.  In that case an anonymous command is defined and bound.

     Instead of a string, this can also be a list of two strings, in which case the first string is used as the short argument (which can also be specified using :shortarg) and the second as the long argument (which can also be specified using :argument).

     Only the long argument is displayed in the popup buffer.  See transient-detect-key-conflicts for how the short argument may be used.

     Unless the class is specified explicitly, the appropriate class is guessed based on the long argument.  If the argument ends with = (e.g., --format=) then transient-option is used, otherwise transient-switch.

Finally, details can be specified using optional KEYWORD-VALUE pairs. Each keyword has to be a keyword symbol, either :class or a keyword argument supported by the constructor of that class.  See Suffix Slots.

Defining Suffix and Infix Commands
==================================

Note that an infix is a special kind of suffix.  Depending on context ``suffixes'' means ``suffixes (including infixes)'' or ``non-infix suffixes''.

 -- Macro: transient-define-suffix name arglist [docstring] [keyword value]... body...
     This macro defines NAME as a transient suffix command.

     ARGLIST are the arguments that the command takes. DOCSTRING is the documentation string and is optional.

     These arguments can optionally be followed by keyword-value pairs. Each keyword has to be a keyword symbol, either :class or a keyword argument supported by the constructor of that class.  The transient-suffix class is used if the class is not specified explicitly.

     The BODY must begin with an interactive form that matches ARGLIST. The infix arguments are usually accessed by using transient-args inside interactive.

 -- Macro: transient-define-infix name arglist [docstring] [keyword value]...
     This macro defines NAME as a transient infix command.

     ARGLIST is always ignored (but mandatory never-the-less) and reserved for future use.  DOCSTRING is the documentation string and is optional.

     At least one key-value pair is required.  All transient infix commands are equal to each other (but not eq).  It is meaningless to define an infix command, without providing at least one keyword argument (usually :argument or :variable, depending on the class). The suffix class defaults to transient-switch and can be set using the :class keyword.

     The function definition is always:

          (lambda ()
            (interactive)
            (let ((obj (transient-suffix-object)))
              (transient-infix-set obj (transient-infix-read obj)))
            (transient--show))

     transient-infix-read and transient-infix-set are generic functions. Different infix commands behave differently because the concrete methods are different for different infix command classes.  In rare cases the above command function might not be suitable, even if you define your own infix command class.  In that case you have to use transient-define-suffix to define the infix command and use t as the value of the :transient keyword.

 -- Macro: transient-define-argument name arglist [docstring] [keyword value]...
     This macro defines NAME as a transient infix command.

     This is an alias for transient-define-infix.  Only use this alias to define an infix command that actually sets an infix argument. To define an infix command that, for example, sets a variable, use transient-define-infix instead.

Using Infix Arguments
=====================

The functions and the variables described below allow suffix commands to access the value of the transient from which they were invoked; which is the value of its infix arguments.  These variables are set when the user invokes a suffix command that exits the transient, but before actually calling the command.

When returning to the command-loop after calling the suffix command, the arguments are reset to nil (which causes the function to return nil too).

Like for Emacs's prefix arguments, it is advisable, but not mandatory, to access the infix arguments inside the command's interactive form. The preferred way of doing that is to call the transient-args function, which for infix arguments serves about the same purpose as prefix-arg serves for prefix arguments.

 -- Function: transient-args prefix
     This function returns the value of the transient prefix command PREFIX.

     If the current command was invoked from the transient prefix command PREFIX, then it returns the active infix arguments.  If the current command was not invoked from PREFIX, then it returns the set, saved or default value for PREFIX.

 -- Function: transient-arg-value arg args
     This function return the value of ARG as it appears in ARGS.

     For a switch a boolean is returned.  For an option the value is returned as a string, using the empty string for the empty value, or nil if the option does not appear in ARGS.

 -- Function: transient-suffixes prefix
     This function returns the suffixes of the transient prefix command PREFIX.  This is a list of objects.  This function should only be used if you need the objects (as opposed to just their values) and if the current command is not being invoked from PREFIX.

 -- Variable: transient-current-suffixes
     The suffixes of the transient from which this suffix command was invoked.  This is a list of objects.  Usually it is sufficient to instead use the function transient-args, which returns a list of values.  In complex cases it might be necessary to use this variable instead, i.e., if you need access to information beside the value.

 -- Variable: transient-current-prefix
     The transient from which this suffix command was invoked.  The returned value is a transient-prefix object, which holds information associated with the transient prefix command.

 -- Variable: transient-current-command
     The transient from which this suffix command was invoked.  The returned value is a symbol, the transient prefix command.

Transient State
===============

Invoking a transient prefix command ``activates'' the respective transient, i.e., it puts a transient keymap into effect, which binds the transient's infix and suffix commands.

The default behavior while a transient is active is as follows:

  * Invoking an infix command does not affect the transient state; the transient remains active.

  * Invoking a (non-infix) suffix command ``deactivates'' the transient state by removing the transient keymap and performing some additional cleanup.

  * Invoking a command that is bound in a keymap other than the transient keymap is disallowed and trying to do so results in a warning.  This does not ``deactivate'' the transient.

The behavior can be changed for all suffixes of a particular prefix and/or for individual suffixes.  The values should nearly always be booleans, but certain functions, called ``pre-commands'', can also be used.  These functions are named transient--do-VERB, and the symbol VERB can be used as a shorthand.

A boolean is interpreted as answering the question "does the transient stay active, when this command is invoked?"  t means that the transient stays active, while nil means that invoking the command exits the transient.

Note that when the suffix is a ``sub-prefix'', invoking that command always activates that sub-prefix, causing the outer prefix to no longer be active and displayed.  Here t means that when you exit the inner prefix, then the outer prefix becomes active again, while nil means that all outer prefixes are exited at once.

  * The behavior for non-suffixes can be set for a particular prefix, by the prefix's transient-non-suffix slot to a boolean, a suitable pre-command function, or a shorthand for such a function.  See Pre-commands for Non-Suffixes.

  * The common behavior for the suffixes of a particular prefix can be set using the prefix's transient-suffixes slot.

     The value specified in this slot does not affect infixes.  Because it affects both regular suffixes as well as sub-prefixes, which have different needs, it is best to avoid explicitly specifying a function.

  * The behavior of an individual suffix can be changed using its transient slot.  While it is usually best to use a boolean, for this slot it can occasionally make sense to specify a function explicitly.

     Note that this slot can be set when defining a suffix command using transient-define-suffix and/or in the definition of the prefix.  If set in both places, then the latter takes precedence, as usual.

The available pre-command functions are documented in the following sub-sections.  They are called by transient--pre-command, a function on pre-command-hook, and the value that they return determines whether the transient is exited.  To do so the value of one of the constants transient--exit or transient--stay is used (that way we don't have to remember if t means ``exit'' or ``stay'').

Additionally, these functions may change the value of this-command (which explains why they have to be called using pre-command-hook), call transient-export, transient--stack-zap or transient--stack-push; and set the values of transient--exitp, transient--helpp or transient--editp.

For completeness sake, some notes about complications:

  * The transient-ness of certain built-in suffix commands is specified using transient-predicate-map.  This is a special keymap, which binds commands to pre-commands (as opposed to keys to commands) and takes precedence over the prefix's transient-suffix slot, but not the suffix's transient slot.

  * While a sub-prefix is active we nearly always want C-g to take the user back to the ``super-prefix'', even when the other suffixes don't do that.  However, in rare cases this may not be desirable, and that makes the following complication necessary:

     For transient-suffix objects the transient slot is unbound.  We can ignore that for the most part because nil and the slot being unbound are treated as equivalent, and mean ``do exit''.  That isn't actually true for suffixes that are sub-prefixes though.  For such suffixes unbound means ``do exit but allow going back'', which is the default, while nil means ``do exit permanently'', which requires that slot to be explicitly set to that value.

Pre-commands for Infixes
------------------------

The default for infixes is transient--do-stay.  This is also the only function that makes sense for infixes, which is why this predicate is used even if the value of the prefix's transient-suffix slot is t.  In extremely rare cases, one might want to use something else, which can be done by setting the infix's transient slot directly.

 -- Function: transient--do-stay
     Call the command without exporting variables and stay transient.

Pre-commands for Suffixes
-------------------------

By default, invoking a suffix causes the transient to be exited.

The behavior for an individual suffix command can be changed by setting its transient slot to a boolean (which is highly recommended), or to one of the following pre-commands.

 -- Function: transient--do-exit
     Call the command after exporting variables and exit the transient.

 -- Function: transient--do-return
     Call the command after exporting variables and return to the parent prefix.  If there is no parent prefix, then call transient--do-exit.

 -- Function: transient--do-call
     Call the command after exporting variables and stay transient.

The following pre-commands are only suitable for sub-prefixes.  It is not necessary to explicitly use these predicates because the correct predicate is automatically picked based on the value of the transient slot for the sub-prefix itself.

 -- Function: transient--do-recurse
     Call the transient prefix command, preparing for return to active transient.

     Whether we actually return to the parent transient is ultimately under the control of each invoked suffix.  The difference between this pre-command and transient--do-stack is that it changes the value of the transient-suffix slot to t.

     If there is no parent transient, then only call this command and skip the second step.

 -- Function: transient--do-stack
     Call the transient prefix command, stacking the active transient. Push the active transient to the transient stack.

     Unless transient--do-recurse is explicitly used, this pre-command is automatically used for suffixes that are prefixes themselves, i.e., for sub-prefixes.

 -- Function: transient--do-replace
     Call the transient prefix command, replacing the active transient. Do not push the active transient to the transient stack.

     Unless transient--do-recurse is explicitly used, this pre-command is automatically used for suffixes that are prefixes themselves, i.e., for sub-prefixes.

 -- Function: transient--do-suspend
     Suspend the active transient, saving the transient stack.

     This is used by the command transient-suspend and optionally also by ``external events'' such as handle-switch-frame.  Such bindings should be added to transient-predicate-map.

Pre-commands for Non-Suffixes
-----------------------------

By default, non-suffixes (commands that are bound in other keymaps beside the transient keymap) cannot be invoked.  Trying to invoke such a command results in a warning and the transient stays active.

If you want a different behavior, then set the transient-non-suffix slot of the transient prefix command.  The value should be a boolean, answering the question, "is it allowed to invoke non-suffix commands?, a pre-command function, or a shorthand for such a function.

If the value is t, then non-suffixes can be invoked, when it is nil (the default) then they cannot be invoked.

The only other recommended value is leave.  If that is used, then non-suffixes can be invoked, but if one is invoked, then that exits the transient.

 -- Function: transient--do-warn
     Call transient-undefined and stay transient.

 -- Function: transient--do-stay
     Call the command without exporting variables and stay transient.

 -- Function: transient--do-leave
     Call the command without exporting variables and exit the transient.

Special Pre-Commands
--------------------

 -- Function: transient--do-quit-one
     If active, quit help or edit mode, else exit the active transient.

     This is used when the user pressed C-g.

 -- Function: transient--do-quit-all
     Exit all transients without saving the transient stack.

     This is used when the user pressed C-q.

 -- Function: transient--do-suspend
     Suspend the active transient, saving the transient stack.

     This is used when the user pressed C-z.

Classes and Methods
*******************

Transient uses classes and generic functions to make it possible to define new types of suffix commands that are similar to existing types, but behave differently in some aspects.  It does the same for groups and prefix commands, though at least for prefix commands that currently appears to be less important.

Every prefix, infix and suffix command is associated with an object, which holds information that controls certain aspects of its behavior. This happens in two ways.

  * Associating a command with a certain class gives the command a type. This makes it possible to use generic functions to do certain things that have to be done differently depending on what type of command it acts on.

     That in turn makes it possible for third-parties to add new types without having to convince the maintainer of Transient that that new type is important enough to justify adding a special case to a dozen or so functions.

  * Associating a command with an object makes it possible to easily store information that is specific to that particular command.

     Two commands may have the same type, but obviously their key bindings and descriptions still have to be different, for example.

     The values of some slots are functions.  The reader slot for example holds a function that is used to read a new value for an infix command.  The values of such slots are regular functions.

     Generic functions are used when a function should do something different based on the type of the command, i.e., when all commands of a certain type should behave the same way but different from the behavior for other types.  Object slots that hold a regular function as value are used when the task that they perform is likely to differ even between different commands of the same type.

Group Classes
=============

The type of a group can be specified using the :class property at the beginning of the class specification, e.g., [:class transient-columns ...] in a call to transient-define-prefix.

  * The abstract transient-child class is the base class of both transient-group (and therefore all groups) as well as of transient-suffix (and therefore all suffix and infix commands).

     This class exists because the elements (or ``children'') of certain groups can be other groups instead of suffix and infix commands.

  * The abstract transient-group class is the superclass of all other group classes.

  * The transient-column class is the simplest group.

     This is the default ``flat'' group.  If the class is not specified explicitly and the first element is not a vector (i.e., not a group), then this class is used.

     This class displays each element on a separate line.

  * The transient-row class displays all elements on a single line.

  * The transient-columns class displays commands organized in columns.

     Direct elements have to be groups whose elements have to be commands or strings.  Each subgroup represents a column.  This class takes care of inserting the subgroups' elements.

     This is the default ``nested'' group.  If the class is not specified explicitly and the first element is a vector (i.e., a group), then this class is used.

  * The transient-subgroups class wraps other groups.

     Direct elements have to be groups whose elements have to be commands or strings.  This group inserts an empty line between subgroups. The subgroups themselves are responsible for displaying their elements.

Group Methods
=============

 -- Function: transient-setup-children group children
     This generic function can be used to setup the children or a group.

     The default implementation usually just returns the children unchanged, but if the setup-children slot of GROUP is non-nil, then it calls that function with CHILDREN as the only argument and returns the value.

     The children are given as a (potentially empty) list consisting of either group or suffix specifications.  These functions can make arbitrary changes to the children including constructing new children from scratch.

 -- Function: transient--insert-group group
     This generic function formats the group and its elements and inserts the result into the current buffer, which is a temporary buffer. The contents of that buffer are later inserted into the popup buffer.

     Functions that are called by this function may need to operate in the buffer from which the transient was called.  To do so they can temporarily make the transient--source-buffer the current buffer.

Prefix Classes
==============

Currently the transient-prefix class is being used for all prefix commands and there is only a single generic function that can be specialized based on the class of a prefix command.

 -- Function: transient--history-init obj
     This generic function is called while setting up the transient and is responsible for initializing the history slot.  This is the transient-wide history; many individual infixes also have a history of their own.

     The default (and currently only) method extracts the value from the global variable transient-history.

A transient prefix command's object is stored in the transient--prefix property of the command symbol.  While a transient is active, a clone of that object is stored in the variable transient--prefix.  A clone is used because some changes that are made to the active transient's object should not affect later invocations.

Suffix Classes
==============

  * All suffix and infix classes derive from transient-suffix, which in turn derives from transient-child, from which transient-group also derives (see Group Classes).

  * All infix classes derive from the abstract transient-infix class, which in turn derives from the transient-suffix class.

     Infixes are a special type of suffixes.  The primary difference is that infixes always use the transient--do-stay pre-command, while non-infix suffixes use a variety of pre-commands (see Transient State).  Doing that is most easily achieved by using this class, though theoretically it would be possible to define an infix class that does not do so.  If you do that then you get to implement many methods.

     Also, infixes and non-infix suffixes are usually defined using different macros (see Defining Suffix and Infix Commands).

  * Classes used for infix commands that represent arguments should be derived from the abstract transient-argument class.

  * The transient-switch class (or a derived class) is used for infix arguments that represent command-line switches (arguments that do not take a value).

  * The transient-option class (or a derived class) is used for infix arguments that represent command-line options (arguments that do take a value).

  * The transient-switches class can be used for a set of mutually exclusive command-line switches.

  * The transient-files class can be used for a -- argument that indicates that all remaining arguments are files.

  * Classes used for infix commands that represent variables should derived from the abstract transient-variable class.

  * The transient-information class is special in that suffixes that use this class are not associated with a command and thus also not with any key binding.  Such suffixes are only used to display arbitrary information, and that anywhere a suffix can appear.  Display-only suffix specifications take this form:

          ([LEVEL] :info DESCRIPTION [KEYWORD VALUE]...)

     The :info keyword argument replaces the :description keyword used for other suffix classes.  Other keyword arguments that you might want to set, include :face, predicate keywords (such as :if), and :format. By default the value of :format includes %k, which for this class is replaced with the empty string or spaces, if keys are being padded in the containing group.

Magit defines additional classes, which can serve as examples for the fancy things you can do without modifying Transient.  Some of these classes will likely get generalized and added to Transient.  For now they are very much subject to change and not documented.

Suffix Methods
==============

To get information about the methods implementing these generic functions use describe-function.

Suffix Value Methods
--------------------

 -- Function: transient-init-value obj
     This generic function sets the initial value of the object OBJ.

     This function is called for all suffix commands, but unless a concrete method is implemented this falls through to the default implementation, which is a noop.  In other words this usually only does something for infix commands, but note that this is not implemented for the abstract class transient-infix, so if your class derives from that directly, then you must implement a method.

 -- Function: transient-infix-read obj
     This generic function determines the new value of the infix object OBJ.

     This function merely determines the value; transient-infix-set is used to actually store the new value in the object.

     For most infix classes this is done by reading a value from the user using the reader specified by the reader slot (using the transient-infix-value method described below).

     For some infix classes the value is changed without reading anything in the minibuffer, i.e., the mere act of invoking the infix command determines what the new value should be, based on the previous value.

 -- Function: transient-prompt obj
     This generic function returns the prompt to be used to read infix object OBJ's value.

 -- Function: transient-infix-set obj value
     This generic function sets the value of infix object OBJ to VALUE.

 -- Function: transient-infix-value obj
     This generic function returns the value of the suffix object OBJ.

     This function is called by transient-args (which see), meaning this function is how the value of a transient is determined so that the invoked suffix command can use it.

     Currently most values are strings, but that is not set in stone. nil is not a value, it means ``no value''.

     Usually only infixes have a value, but see the method for transient-suffix.

 -- Function: transient-init-scope obj
     This generic function sets the scope of the suffix object OBJ.

     The scope is actually a property of the transient prefix, not of individual suffixes.  However it is possible to invoke a suffix command directly instead of from a transient.  In that case, if the suffix expects a scope, then it has to determine that itself and store it in its scope slot.

     This function is called for all suffix commands, but unless a concrete method is implemented this falls through to the default implementation, which is a noop.

Suffix Format Methods
---------------------

 -- Function: transient-format obj
     This generic function formats and returns OBJ for display.

     When this function is called, then the current buffer is some temporary buffer.  If you need the buffer from which the prefix command was invoked to be current, then do so by temporarily making transient--source-buffer current.

 -- Function: transient-format-key obj
     This generic function formats OBJ's key for display and returns the result.

 -- Function: transient-format-description obj
     This generic function formats OBJ's description for display and returns the result.

 -- Function: transient-format-value obj
     This generic function formats OBJ's value for display and returns the result.

 -- Function: transient-show-help obj
     Show help for the prefix, infix or suffix command represented by OBJ.

     For prefixes, show the info manual, if that is specified using the info-manual slot.  Otherwise, show the manpage if that is specified using the man-page slot.  Otherwise, show the command's documentation string.

     For suffixes, show the command's documentation string.

     For infixes, show the manpage if that is specified.  Otherwise show the command's documentation string.

Prefix Slots
============

  * show-help, man-page or info-manual can be used to specify the documentation for the prefix and its suffixes.  The command transient-help uses the method transient-show-help (which see) to lookup and use these values.

  * history-key If multiple prefix commands should share a single value, then this slot has to be set to the same value for all of them.  You probably don't want that.

  * transient-suffix and transient-non-suffix play a part when determining whether the currently active transient prefix command remains active/transient when a suffix or arbitrary non-suffix command is invoked.  See Transient State.

  * refresh-suffixes Normally suffix objects and keymaps are only setup once, when the prefix is invoked.  Setting this to t, causes them to be recreated after every command.  This is useful when using :if... predicates, and those need to be rerun for some reason.  Doing this is somewhat costly, and there is a risk of losing state, so this is disabled by default and still considered experimental.

  * incompatible A list of lists.  Each sub-list specifies a set of mutually exclusive arguments.  Enabling one of these arguments causes the others to be disabled.  An argument may appear in multiple sub-lists.  Arguments must me given in the same form as used in the argument or argument-format slot of the respective suffix objects, usually something like --switch or --option=%s.  For options and transient-switches suffixes it is also possible to match against a specific value, as returned by transient-infix-value, for example, --option=one.

  * scope For some transients it might be necessary to have a sort of secondary value, called a ``scope''.  See transient-define-prefix.

Internal Prefix Slots
---------------------

These slots are mostly intended for internal use.  They should not be set in calls to transient-define-prefix.

  * prototype When a transient prefix command is invoked, then a clone of that object is stored in the global variable transient--prefix and the prototype is stored in the clone's prototype slot.

  * command The command, a symbol.  Each transient prefix command consists of a command, which is stored in a symbol's function slot and an object, which is stored in the transient--prefix property of the same symbol.

  * level The level of the prefix commands.  The suffix commands whose layer is equal or lower are displayed.  see Enabling and Disabling Suffixes.

  * value The likely outdated value of the prefix.  Instead of accessing this slot directly you should use the function transient-get-value, which is guaranteed to return the up-to-date value.

  * history and history-pos are used to keep track of historic values. Unless you implement your own transient-infix-read method you should not have to deal with these slots.

Suffix Slots
============

Here we document most of the slots that are only available for suffix objects.  Some slots are shared by suffix and group objects, they are documented in Predicate Slots.

Also see Suffix Classes.

Slots of transient-suffix
-------------------------

  * key The key, a key vector or a key description string.

  * command The command, a symbol.

  * transient Whether to stay transient.  See Transient State.

  * format The format used to display the suffix in the popup buffer. It must contain the following %-placeholders:

       * %k For the key.

       * %d For the description.

       * %v For the infix value.  Non-infix suffixes don't have a value.

  * description The description, either a string or a function, which is called with zero or one argument (the suffix object), and returns a string.

  * face Face used for the description.  In simple cases it is easier to use this instead of using a function as description and adding the styling there.  face is appended using add-face-text-property.

  * show-help A function used to display help for the suffix.  If unspecified, the prefix controls how help is displayed for its suffixes.

Slots of transient-infix
------------------------

Some of these slots are only meaningful for some of the subclasses. They are defined here anyway to allow sharing certain methods.

  * argument The long argument, e.g., --verbose.

  * shortarg The short argument, e.g., -v.

  * value The value.  Should not be accessed directly.

  * init-value Function that is responsible for setting the object's value.  If bound, then this is called with the object as the only argument.  Usually this is not bound, in which case the object's primary transient-init-value method is called instead.

  * unsavable Whether the value of the suffix is not saved as part of the prefixes.

  * multi-value For options, whether the option can have multiple values.  If this is non-nil, then the values are read using completing-read-multiple by default and if you specify your own reader, then it should read the values using that function or similar.

     Supported non-nil values are:

       * Use rest for an option that can have multiple values.  This is useful e.g., for an -- argument that indicates that all remaining arguments are files (such as git log -- file1 file2).

          In the list returned by transient-args such an option and its values are represented by a single list of the form (ARGUMENT . VALUES).

       * Use repeat for an option that can be specified multiple times.

          In the list returned by transient-args each instance of the option and its value appears separately in the usual from, for example: ("--another-argument" "--option=first" "--option=second").

     In both cases the option's values have to be specified in the default value of a prefix using the same format as returned by transient-args, e.g., ("--other" "--o=1" "--o=2" ("--" "f1" "f2")).

  * always-read For options, whether to read a value on every invocation. If this is nil, then options that have a value are simply unset and have to be invoked a second time to set a new value.

  * allow-empty For options, whether the empty string is a valid value.

  * history-key The key used to store the history.  This defaults to the command name.  This is useful when multiple infixes should share the same history because their values are of the same kind.

  * reader The function used to read the value of an infix.  Not used for switches.  The function takes three arguments, PROMPT, INITIAL-INPUT and HISTORY, and must return a string.

  * prompt The prompt used when reading the value, either a string or a function that takes the object as the only argument and which returns a prompt string.

  * choices A list of valid values, or a function that returns such a list.  The latter is not implemented for transient-switches, because I couldn't think of a use-case.  How exactly the choices are used varies depending on the class of the suffix.

Slots of transient-variable
---------------------------

  * variable The variable.

Slots of transient-switches
---------------------------

  * argument-format The display format.  Must contain %s, one of the choices is substituted for that.  E.g., --%s-order.

  * argument-regexp The regexp used to match any one of the switches. E.g., \\(--\\(topo\\|author-date\\|date\\)-order\\).

Predicate Slots
===============

Suffix and group objects share some predicate slots that control whether a group or suffix should be available depending on some state. Only one of these slots can be used at the same time.  It is undefined what happens if you use more than one.

  * if Enable if predicate returns non-nil.

  * if-not Enable if predicate returns nil.

  * if-non-nil Enable if variable's value is non-nil.

  * if-nil Enable if variable's value is nil.

  * if-mode Enable if major-mode matches value.

  * if-not-mode Enable if major-mode does not match value.

  * if-derived Enable if major-mode derives from value.

  * if-not-derived Enable if major-mode does not derive from value.

By default these predicates run when the prefix command is invoked, but this can be changes, using the refresh-suffixes prefix slot. See Prefix Slots.

One more slot is shared between group and suffix classes, level.  Like the slots documented above, it is a predicate, but it is used for a different purpose.  The value has to be an integer between 1 and 7.  level controls whether a suffix or a group should be available depending on user preference. See Enabling and Disabling Suffixes.

FAQ
***

Can I control how the popup buffer is displayed?
================================================

Yes, see transient-display-buffer-action in Configuration.

How can I copy text from the popup buffer?
==========================================

To be able to mark text in Transient's popup buffer using the mouse, you have to add the below binding.  Note that for technical reasons, the region won't be visualized, while doing so.  After you have quit the transient popup, you will be able to yank it in another buffer.

     (keymap-set transient-predicate-map
                 "<mouse-set-region>"
                 #'transient--do-stay)

How can I autoload prefix and suffix commands?
==============================================

If your package only supports Emacs 30, just prefix the definition with ;;;###autoload.  If your package supports released versions of Emacs, you unfortunately have to use a long form autoload comment as described in Autoload (elisp).

     ;;;###autoload (autoload 'magit-dispatch "magit" nil t)
     (transient-define-prefix magit-dispatch ()
       ...)

How does Transient compare to prefix keys and universal arguments?
==================================================================

See https://github.com/magit/transient/wiki/Comparison-with-prefix-keys-and-universal-arguments.

How does Transient compare to Magit-Popup and Hydra?
====================================================

See https://github.com/magit/transient/wiki/Comparison-with-other-packages.

Why did some of the key bindings change?
========================================

You may have noticed that the bindings for some of the common commands do not have the prefix C-x and that furthermore some of these commands are grayed out while others are not.  That unfortunately is a bit confusing if the section of common commands is not shown permanently, making the following explanation necessary.

The purpose of usually hiding that section but showing it after the user pressed the respective prefix key is to conserve space and not overwhelm users with too much noise, while allowing the user to quickly list common bindings on demand.

That however should not keep us from using the best possible key bindings.  The bindings that do use a prefix do so to avoid wasting too many non-prefix bindings, keeping them available for use in individual transients.  The bindings that do not use a prefix and that are not grayed out are very important bindings that are always available, even when invoking the ``common command key prefix'' or any other transient-specific prefix.  The non-prefix keys that are grayed out however, are not available when any incomplete prefix key sequence is active.  They do not use the ``common command key prefix'' because it is likely that users want to invoke them several times in a row and e.g., M-p M-p M-p is much more convenient than C-x M-p C-x M-p C-x M-p.

You may also have noticed that the ``Set'' command is bound to C-x s, while Magit-Popup used to bind C-c C-c instead.  I have seen several users praise the latter binding (sic), so I did not change it willy-nilly.  The reason that I changed it is that using different prefix keys for different common commands, would have made the temporary display of the common commands even more confusing, i.e., after pressing C-c all the bindings that begin with the C-x prefix would be grayed out.

Using a single prefix for common commands key means that all other potential prefix keys can be used for transient-specific commands without the section of common commands also popping up.  C-c in particular is a prefix that I want to (and already do) use for Magit, and also using that for a common command would prevent me from doing so.

(Also see the next question.)

Why does q not quit popups anymore?
===================================

I agree that q is a good binding for commands that quit something. This includes quitting whatever transient is currently active, but it also includes quitting whatever it is that some specific transient is controlling.  The transient magit-blame for example binds q to the command that turns magit-blame-mode off.

So I had to decide if q should quit the active transient (like Magit-Popup used to) or whether C-g should do that instead, so that q could be bound in individual transient to whatever commands make sense for them.  Because all other letters are already reserved for use by individual transients, I have decided to no longer make an exception for q.

If you want to get q's old binding back then you can do so.  Doing that is a bit more complicated than changing a single key binding, so I have implemented a function, transient-bind-q-to-quit that makes the necessary changes.  See its documentation string for more information.

GNU General Public License
**************************

     [file gpl.texi not included]