Transient User and Developer Manual

2.1 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.

2.2 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 doc 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.

2.3 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.

2.4 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. ¹

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.

2.5 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.

2.6 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 doc string, for non-infix suffixes this is usually appropriate.

2.7 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.

2.8 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).

2.9 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 (elisp)Choosing Window, 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 (elisp)Buffer Display Action Functions, and see (elisp)Buffer Display Action Alists.

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), then the buffer also has no mode-line, but a thin line is drawn instead, using the background color of the face transient-separator. Text-mode frames cannot display thin lines, and therefore fall back to treating line like nil.

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

User Option: transient-semantic-coloring ¶

This option controls whether prefixes and suffixes are colored in a Hydra-like fashion.

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.

For more information about how Hydra uses colors see https://github.com/abo-abo/hydra#color and https://oremacs.com/2015/02/19/hydra-colors-reloaded.

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.

4.1 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.

4.2 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
• Suffix Specifications

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

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

4.3 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.

The keyword-value pairs are mandatory. All transient infix commands are equal to each other (but not eq), so it is meaningless to define an infix command without also setting at least :class and one other keyword (which it is depends on the used class, usually :argument or :variable).

Each keyword has to be a keyword symbol, either :class or a keyword argument supported by the constructor of that class. The transient-switch class is used if the class is not specified explicitly.

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.

4.4 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’ 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.

4.5 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.

But these are just the defaults. Whether a certain command deactivates or “exits” the transient is configurable. There is more than one way in which a command can be “transient” or “non-transient”; the exact behavior is implemented by calling a so-called “pre-command” function. Whether non-suffix commands are allowed to be called is configurable per transient.

• The transient-ness of suffix commands (including infix commands) is controlled by the value of their transient slot, which can be set either when defining the command or when adding a binding to a transient while defining the respective transient prefix command.

  Valid values are booleans and the pre-commands described below.

  • t is equivalent to transient--do-stay.
  • nil is equivalent to transient--do-exit.
  • If transient is unbound (and that is actually the default for non-infix suffixes) then the value of the prefix’s transient-suffix slot is used instead. The default value of that slot is nil, so the suffix’s transient slot being unbound is essentially equivalent to it being nil.
• A suffix command can be a prefix command itself, i.e., a “sub-prefix”. While a sub-prefix is active we nearly always want C-g to take the user back to the “super-prefix”. 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, as stated above, nil and the slot being unbound are 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.

• 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 transient slot.

The available pre-command functions are documented below. 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.

Pre-commands for Infixes

The default for infixes is transient--do-stay. This is also the only function that makes sense for infixes.

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.

If you want a different default behavior for a certain transient prefix command, then set its :transient-suffix slot. The value can be a boolean, answering the question "does the transient stay active, when a suffix command is invoked?" t means that the transient stays active, while nil means that invoking a suffix exits the transient. In either case, the exact behavior depends on whether the suffix is itself a prefix (i.e., a sub-prefix), an infix or a regular suffix.

The behavior for an individual suffix command can be changed by setting its transient slot 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 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 suitable for sub-prefixes. Only the first should ever explicitly be set as the value of the transient slot.

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-replace is that it changes the value of the transient-suffix slot to transient--do-return.

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

Function: transient--do-replace ¶

Call the transient prefix command, replacing the active transient.

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 can be a boolean, answering the question, "is it allowed to invoke non-suffix commands?"

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

The only other recommended value is transient--do-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.

5.1 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.

5.2 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.

5.3 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.

5.4 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.

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.

5.5 Suffix Methods

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

• Suffix Value Methods
• Suffix Format Methods

5.6 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.
• 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.
• 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.

5.7 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 that is called with no argument and returns a string.
• 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. How exactly that is used depends on the class of the object.

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\\).

5.8 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.

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.

6.1 Comparison With Prefix Keys and Prefix Arguments

While transient commands were inspired by regular prefix keys and prefix arguments, they are also quite different and much more complex.

The following diagrams illustrate some of the differences.

• ‘(c)’ represents a return to the command loop.
• ‘(+)’ represents the user’s choice to press one key or another.
• ‘{WORD}’ are possible behaviors.
• ‘{NUMBER}’ is a footnote.

Regular Prefix Commands

See (elisp)Prefix Keys.

                                  ,--> command1 --> (c)
                                  |
(c)-(+)-> prefix command or key --+--> command2 --> (c)
                                  |
                                  `--> command3 --> (c)

Regular Prefix Arguments

See (elisp)Prefix Command Arguments.

        ,----------------------------------,
        |                                  |
        v                                  |
(c)-(+)---> prefix argument command --(c)-(+)-> any command --> (c)
               |                                        ^        |
               |                                        |        |
               `-- sets or changes --, ,-- maybe used --'        |
                                     | |                         |
                                     v |                         |
                          prefix argument state                  |
                                      ^                          |
                                      |                          |
                                      `-------- discards --------'

Transients

(∩｀-´)⊃━☆ﾟ.*･｡ﾟ

This diagram ignores the infix value and external state:

(c)
 |        ,- {stay} ------<-,-<------------<-,-<---,
(+)       |                 |                |     |
 |        |                 |                |     |
 |        |   ,--> infix1 --|                |     |
 |        |   |             |                |     |
 |        |   |--> infix2 --|                |     |
 v        v   |             |                |     |
 prefix -(c)-(+)-> infix3 --'                ^     |
              |                              |     |
              |---------------> suffix1 -->--|     |
              |                              |     |
              |---------------> suffix2 ----{1}------> {exit} --> (c)
              |                                    |
              |---------------> suffix3 -------------> {exit} --> (c)
              |                                    |
              `--> any command --{2}-> {warn} -->--|
                                  |                |
                                  |--> {noop} -->--|
                                  |                |
                                  |--> {call} -->--'
                                  |
                                  `------------------> {exit} --> (c)

This diagram takes the infix value into account to an extend, while still ignoring external state:

(c)
 |        ,- {stay} ------<-,-<------------<-,-<---,
(+)       |                 |                |     |
 |        |                 |                |     |
 |        |   ,--> infix1 --|                |     |
 |        |   |    |        |                |     |
 |        |   ,--> infix2 --|                |     |
 v        v   |    |        |                |     |
 prefix -(c)-(+)-> infix3 --'                |     |
              |    |                         ^     |
              |    |                         |     |
              |---------------> suffix1 -->--|     |
              |    |             ^           |     |
              |    |             |           |     |
              |---------------> suffix2 ----{1}------> {exit} --> (c)
              |    |             ^                 |     |
              |    |             |                 |     v
              |    |             |                 |     |
              |---------------> suffix3 -------------> {exit} --> (c)
              |    |             ^                 |     |
              | sets             |                 |     v
              |    |             maybe             |     |
              |    |             used              |     |
              |    |             |                 |     |
              |    |     infix --'                 |     |
              |    `---> value                     |     |
              |           ^                        |     |
              |           |                        |     |
              |       hides                        |     |
              |           |                        |     |
              |           `--------------------------<---|
              |                                    |     |
              `--> any command --{2}-> {warn} -->--|     |
                                  |                |     |
                                  |--> {noop} -->--|     |
                                  |                |     |
                                  |--> {call} -->--'     ^
                                  |                      |
                                  `------------------> {exit} --> (c)

This diagram provides more information about the infix value and also takes external state into account.

                                       ,----sets--- "anything"
                                       |
                                       v
                      ,---------> external
                      |           state
                      |            | |
                      |  initialized |                      ☉‿⚆
                   sets         from |
                      |            | maybe
                      | ,----------' used
                      | |            |
(c)                   | |            v
 |        ,- {stay} --|---<-,-<------|-----<-,-<---,
(+)       |           | |   |        |       |     |
 |        |           | v   |        |       |     |
 |        |   ,--> infix1 --|        |       |     |
 |        |   |       | |   |        |       |     |
 |        |   |       | v   |        |       |     |
 |        |   ,--> infix2 --|        |       |     |
 |        |   |    | ^      |        |       |     |
 v        v   |    | |      |        |       |     |
 prefix -(c)-(+)-> infix3 --'        |       |     |
              |    | ^               |       ^     |
              |    | |               v       |     |
              |---------------> suffix1 -->--|     |
              |    | |            ^  |       |     |
              |    | |            |  v       |     |
              |---------------> suffix2 ----{1}------> {exit} --> (c)
              |    | |            ^  |             |     |
              |    | |            |  |             |     v
              |    | |            |  v             |     |
              |---------------> suffix3 -------------> {exit} --> (c)
              |    | |            ^                |     |
              | sets |            |                |     v
              |    | initialized  maybe            |     |
              |    | from         used             |     |
              |    | |            |                |     |
              |    | `-- infix ---'                |     |
              |    `---> value -----------------------------> persistent
              |           ^ ^                      |     |    across
              |           | |                      |     |    invocations -,
              |       hides |                      |     |                 |
              |           | `----------------------------------------------'
              |           |                        |     |
              |           `--------------------------<---|
              |                                    |     |
              `--> any command --{2}-> {warn} -->--|     |
                                  |                |     |
                                  |--> {noop} -->--|     |
                                  |                |     |
                                  |--> {call} -->--'     ^
                                  |                      |
                                  `------------------> {exit} --> (c)

• ‘{1}’ Transients can be configured to be exited when a suffix command is invoked. The default is to do so for all suffixes except for those that are common to all transients and which are used to perform tasks such as providing help and saving the value of the infix arguments for future invocations. The behavior can also be specified for individual suffix commands and may even depend on state.
• ‘{2}’ Transients can be configured to allow the user to invoke non-suffix commands. The default is to not allow that and instead warn the user.

Despite already being rather complex, even the last diagram leaves out many details. Most importantly it implies that the decision whether to remain transient is made later than it actually is made (for the most part a function on pre-command-hook is responsible). But such implementation details are of little relevance to users and are covered elsewhere.

6.2 Comparison With Other Packages

Magit-Popup

Transient is the successor to Magit-Popup (see (magit-popup)Top).

One major difference between these two implementations of the same ideas is that while Transient uses transient keymaps and embraces the command-loop, Magit-Popup implemented an inferior mechanism that does not use transient keymaps and that instead of using the command-loop implements a naive alternative based on read-char.

Magit-Popup does not use classes and generic functions and defining a new command type is near impossible as it involves adding hard-coded special-cases to many functions. Because of that only a single new type was added, which was not already part of Magit-Popup’s initial release.

A lot of things are hard-coded in Magit-Popup. One random example is that the key bindings for switches must begin with - and those for options must begin with =.

Hydra

Hydra (see https://github.com/abo-abo/hydra) is another package that provides features similar to those of Transient.

Both packages use transient keymaps to make a set of commands temporarily available and show the available commands in a popup buffer.

A Hydra “body” is equivalent to a Transient “prefix” and a Hydra “head” is equivalent to a Transient “suffix”. Hydra has no equivalent of a Transient “infix”.

Both hydras and transients can be used as simple command dispatchers. Used like this they are similar to regular prefix commands and prefix keys, except that the available commands are shown in the popup buffer.

(Another package that does this is which-key. It does so automatically for any incomplete key sequence. The advantage of that approach is that no additional work is necessary; the disadvantage is that the available commands are not organized semantically.)

Both Hydra and Transient provide features that go beyond simple command dispatchers:

• Invoking a command from a hydra does not necessarily exit the hydra. That makes it possible to invoke the same command again, but using a shorter key sequence (i.e., the key that was used to enter the hydra does not have to be pressed again).

  Transient supports that too, but for now this feature is not a focus and the interface is a bit more complicated. A very basic example using the current interface:

  (transient-define-prefix outline-navigate ()
    :transient-suffix     'transient--do-stay
    :transient-non-suffix 'transient--do-warn
    [("p" "previous visible heading" outline-previous-visible-heading)
     ("n" "next visible heading" outline-next-visible-heading)])
  

• Transient supports infix arguments; values that are set by infix commands and then consumed by the invoked suffix command(s).

  To my knowledge, Hydra does not support that.

Both packages make it possible to specify how exactly the available commands are outlined:

• With Hydra this is often done using an explicit format string, which gives authors a lot of flexibility and makes it possible to do fancy things.

  The downside of this is that it becomes harder for a user to add additional commands to an existing hydra and to change key bindings.

• Transient allows the author of a transient to organize the commands into groups and the use of generic functions allows authors of transients to control exactly how a certain command type is displayed.

  However while Transient supports giving sections a heading it does not currently support giving the displayed information more structure by, for example, using box-drawing characters.

  That could be implemented by defining a new group class, which lets the author specify a format string. It should be possible to implement that without modifying any existing code, but it does not currently exist.