defvar-keymap: New ':prefix t' abbreviation

* lisp/keymap.el (defvar-keymap): New ':prefix t' abbreviation.
* lisp/emacs-lisp/helper.el (Helper-help-map):
* lisp/vc/pcvs.el (cvs-mode-diff-map):
* lisp/vc/vc-hooks.el (vc-prefix-map):
* lisp/vcursor.el (vcursor-map): Use it.
* doc/lispref/keymaps.texi (Creating Keymaps):
* etc/NEWS: Document it.

doc/lispref/keymaps.texi

@@ -650,11 +650,9 @@ and @var{pairs} to @code{define-keymap}, and uses the result as the
 default value for the variable.  It signals an error if there are
 duplicate key bindings in @var{pairs}.
 
-@var{options} is like the keywords in @code{define-keymap}, but
-there's an additional @code{:doc} keyword that provides the doc
-string for the defined variable.
-
-Here's an example:
+@var{options} is mostly like the keywords in @code{define-keymap}.
+There's an additional @code{:doc} keyword that provides the doc string
+for the defined variable.  Here's an example:
 
 @lisp
 (defvar-keymap eww-textarea-map
@@ -664,6 +662,24 @@ Here's an example:
   "TAB" #'shr-next-link)
 @end lisp
 
+The @code{:prefix} keyword can take an additional value, @code{t}, which
+is an abbreviation for using @var{name} as the value of that option.
+I.e. instead of writing
+
+@lisp
+(defvar-keymap foo-map
+  :prefix 'foo-map
+  ...)
+@end lisp
+
+you can write
+
+@lisp
+(defvar-keymap foo-map
+  :prefix t
+  ...)
+@end lisp
+
 @kindex :repeat
 @kindex repeat-mode
 @cindex repeatable key bindings

etc/NEWS

@@ -3310,6 +3310,12 @@ a remote host.  It must be used in conjunction with the function
 The column number is no longer available; the line number will be
 removed in next Emacs release.
 
++++
+** defvar-keymap can now take a ':prefix t' option.
+This is an abbreviation for using the name of the keymap as the prefix
+command name.  E.g. (defvar-keymap foo-map :prefix t) is equivalent to
+(defvar-keymap foo-map :prefix 'foo-map).
+
 
 * Changes in Emacs 31.1 on Non-Free Operating Systems
 

lisp/emacs-lisp/helper.el

@@ -40,6 +40,7 @@
 
 
 (defvar-keymap Helper-help-map
+  :prefix t
   "m" #'Helper-describe-mode
   "b" #'Helper-describe-bindings
   "c" #'Helper-describe-key-briefly
@@ -48,7 +49,6 @@
   ;;"v" #'Helper-describe-variable
   "?" #'Helper-help-options
   (help-key) #'Helper-help-options)
-(fset 'Helper-help-map Helper-help-map)
 
 (defun Helper-help-scroller ()
   (let ((blurb (or (and (boundp 'Helper-return-blurb)

lisp/keymap.el

@@ -614,9 +614,11 @@ pairs.  Available keywords are:
 :name      If non-nil, this should be a string to use as the menu for
              the keymap in case you use it as a menu with `x-popup-menu'.
 
-:prefix    If non-nil, this should be a symbol to be used as a prefix
-             command (see `define-prefix-command').  If this is the case,
-             this symbol is returned instead of the map itself.
+:prefix    If non-nil, this should be a symbol to make into a prefix command
+             using the new keymap (see `define-prefix-command').
+             That is, store the keymap as the symbol's function definition.
+             In addition, when non-nil, return the symbol instead of the
+             new keymap.
 
 KEY/DEFINITION pairs are as KEY and DEF in `keymap-set'.  KEY can
 also be the special symbol `:menu', in which case DEFINITION
@@ -689,6 +691,9 @@ In addition to the keywords accepted by `define-keymap', this
 macro also accepts a `:doc' keyword, which (if present) is used
 as the variable documentation string.
 
+The `:prefix' keyword can take an additional value, t, which is an
+abbreviation for using VARIABLE-NAME as the prefix command name.
+
 The `:repeat' keyword can also be specified; it controls the
 `repeat-mode' behavior of the bindings in the keymap.  When it is
 non-nil, all commands in the map will have the `repeat-map'
@@ -734,10 +739,17 @@ in the echo area.
         (unless defs
           (error "Uneven number of keywords"))
         (cond
-         ((eq keyword :doc) (setq doc (pop defs)))
-         ((eq keyword :repeat) (setq repeat (pop defs)))
-         (t (push keyword opts)
-            (push (pop defs) opts)))))
+         ((eq keyword :doc)
+          (setq doc (pop defs)))
+         ((eq keyword :repeat)
+          (setq repeat (pop defs)))
+         ((and (eq keyword :prefix) (eq (car defs) t))
+          (setq defs (cdr defs))
+          (push keyword opts)
+          (push `',variable-name opts))
+         (t
+          (push keyword opts)
+          (push (pop defs) opts)))))
     (unless (zerop (% (length defs) 2))
       (error "Uneven number of key/definition pairs: %s" defs))
 

lisp/vc/pcvs.el

@@ -140,6 +140,10 @@
 
 (defvar-keymap cvs-mode-diff-map
   :name "Diff"
+  ;; This is necessary to allow correct handling of
+  ;; \\[cvs-mode-diff-map] in substitute-command-keys.
+  :prefix t
+
   "E" (cons "imerge" #'cvs-mode-imerge)
   "=" #'cvs-mode-diff
   "e" (cons "idiff" #'cvs-mode-idiff)
@@ -150,9 +154,6 @@
   "r" (cons "repository" #'cvs-mode-diff-repository)
   "y" (cons "yesterday" #'cvs-mode-diff-yesterday)
   "v" (cons "vendor" #'cvs-mode-diff-vendor))
-;; This is necessary to allow correct handling of \\[cvs-mode-diff-map]
-;; in substitute-command-keys.
-(fset 'cvs-mode-diff-map cvs-mode-diff-map)
 
 (defvar-keymap cvs-mode-map
   :full t

lisp/vc/vc-hooks.el

@@ -965,6 +965,7 @@ In the latter case, VC mode is deactivated for this buffer."
 ;; in the menu because they don't exist yet when the menu is built.
 ;; (autoload 'vc-prefix-map "vc" nil nil 'keymap)
 (defvar-keymap vc-prefix-map
+  :prefix t
   "a"   #'vc-update-change-log
   "b c" #'vc-create-branch
   "b l" #'vc-print-branch-log
@@ -1003,7 +1004,6 @@ In the latter case, VC mode is deactivated for this buffer."
   "w R" #'vc-move-working-tree
   "w a" #'vc-apply-to-other-working-tree
   "w A" #'vc-apply-root-to-other-working-tree)
-(fset 'vc-prefix-map vc-prefix-map)
 (define-key ctl-x-map "v" 'vc-prefix-map)
 
 (defvar-keymap vc-incoming-prefix-map

lisp/vcursor.el

@@ -467,6 +467,10 @@ scrolling set this.  It is used by the `vcursor-auto-disable' code.")
 
 (defvar-keymap vcursor-map
   :doc "Keymap for vcursor command."
+  ;; This seems unused but was done previously (Emacs 24), so is kept
+  ;; for now.
+  :prefix t
+
   "t"   #'vcursor-use-vcursor-map
 
   "C-p" #'vcursor-previous-line
@@ -495,9 +499,6 @@ scrolling set this.  It is used by the `vcursor-auto-disable' code.")
   "c"   #'vcursor-compare-windows
   "k"   #'vcursor-execute-key
   "M-x" #'vcursor-execute-command)
-;; This seems unused, but it was done as part of define-prefix-command,
-;; so let's keep it for now.
-(fset 'vcursor-map vcursor-map)
 
 ;; If vcursor-key-bindings is already set on loading, bind the keys now.
 ;; This hybrid way of doing it retains compatibility while allowing