Optionally refresh suffixes and keymaps after every command

Closes #157.

docs/transient.org

@@ -1746,6 +1746,13 @@ functions use ~describe-function~.
   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
@@ -1919,6 +1926,10 @@ what happens if you use more than one.
 - ~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

docs/transient.texi

@@ -1990,6 +1990,14 @@ determining whether the currently active transient prefix command
 remains active/transient when a suffix or arbitrary non-suffix
 command is invoked.  See @ref{Transient State}.
 
+@item
+@code{refresh-suffixes} Normally suffix objects and keymaps are only setup
+once, when the prefix is invoked.  Setting this to @code{t}, causes them to
+be recreated after every command.  This is useful when using @code{: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.
+
 @item
 @code{incompatible} A list of lists.  Each sub-list specifies a set of
 mutually exclusive arguments.  Enabling one of these arguments
@@ -2212,6 +2220,10 @@ what happens if you use more than one.
 @code{if-not-derived} Enable if major-mode does not derive from value.
 @end itemize
 
+By default these predicates run when the prefix command is invoked,
+but this can be changes, using the @code{refresh-suffixes} prefix slot.
+See @ref{Prefix Slots}.
+
 One more slot is shared between group and suffix classes, @code{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

lisp/transient.el

@@ -634,6 +634,7 @@ If `transient-save-history' is nil, then do nothing."
    (man-page    :initarg :man-page    :initform nil)
    (transient-suffix     :initarg :transient-suffix     :initform nil)
    (transient-non-suffix :initarg :transient-non-suffix :initform nil)
+   (refresh-suffixes     :initarg :refresh-suffixes     :initform nil)
    (incompatible         :initarg :incompatible         :initform nil)
    (suffix-description   :initarg :suffix-description)
    (variable-pitch       :initarg :variable-pitch       :initform nil)
@@ -1811,10 +1812,8 @@ EDIT may be non-nil."
       ;; Returning from help to edit.
       (setq transient--editp t)))
     (transient--init-objects name layout params)
+    (transient--init-keymaps)
     (transient--history-init transient--prefix)
-    (setq transient--predicate-map (transient--make-predicate-map))
-    (setq transient--transient-map (transient--make-transient-map))
-    (setq transient--redisplay-map (transient--make-redisplay-map))
     (setq transient--original-window (selected-window))
     (setq transient--original-buffer (current-buffer))
     (setq transient--minibuffer-depth (minibuffer-depth))
@@ -1831,8 +1830,15 @@ value.  Otherwise return CHILDREN as is."
       (funcall (oref group setup-children) children)
     children))
 
-(defun transient--init-objects (name layout params)
-  (setq transient--prefix (transient--init-prefix name params))
+(defun transient--init-keymaps ()
+  (setq transient--predicate-map (transient--make-predicate-map))
+  (setq transient--transient-map (transient--make-transient-map))
+  (setq transient--redisplay-map (transient--make-redisplay-map)))
+
+(defun transient--init-objects (&optional name layout params)
+  (if name
+      (setq transient--prefix (transient--init-prefix name params))
+    (setq name (oref transient--prefix command)))
   (setq transient--layout (or layout (transient--init-suffixes name)))
   (setq transient--suffixes (transient--flatten-suffixes transient--layout)))
 
@@ -2014,6 +2020,17 @@ value.  Otherwise return CHILDREN as is."
     ;; that we just added.
     (setq transient--exitp 'replace)))
 
+(defun transient--refresh-transient ()
+  (transient--debug 'refresh-transient)
+  (transient--pop-keymap 'transient--predicate-map)
+  (transient--pop-keymap 'transient--transient-map)
+  (transient--pop-keymap 'transient--redisplay-map)
+  (transient--init-objects)
+  (transient--init-keymaps)
+  (transient--push-keymap 'transient--transient-map)
+  (transient--push-keymap 'transient--redisplay-map)
+  (transient--redisplay))
+
 (defun transient--pre-command ()
   (transient--debug 'pre-command)
   (transient--with-emergency-exit
@@ -2273,6 +2290,8 @@ value.  Otherwise return CHILDREN as is."
                   ;; would have to be used to record that a universal
                   ;; argument is in effect.
                   (not prefix-arg)))
+            ((oref transient--prefix refresh-suffixes)
+             (transient--refresh-transient))
             ((let ((old transient--redisplay-map)
                    (new (transient--make-redisplay-map)))
                (unless (equal old new)