bug#57639: [PATCH] Add new command 'toggle-theme'

[Philip Kaludercic <philipk@posteo.net>]

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Mauro Aranda <maurooaranda@gmail.com> writes:

> Philip Kaludercic <philipk@posteo.net> writes:
>
>> Mauro Aranda <maurooaranda@gmail.com> writes:
>
>>>>> Also, no documentation for these special properties for toggling
>      themes?
>>>>
>>>> Currently no.
>>>
>>> I hope there will be.
>>
>> I had to check the thread again, and the most that was said on the topic
>> was in <87leqo978k.fsf@gnus.org>.  So the idea would be to mention
>> :family, :kind and :background-mode and state that anything else is
>> undefined/shouldn't be used in case we decide to add another property in
>> the future?
>>
>> We should also specify what valid values are.  :family is just a symbol,
>> :background-mode is either 'light or 'dark, but what about :kind?
>
> I'm not really good at this, but something like:
>
> The following properties are supported:
> ':family': The value should be a symbol, the name of the family that the
> theme is part of.  [And insert here the explanation of family that Eli
> gave]
> ':kind': The value should be a symbol.  If a theme is enabled and this
> property has the value color-scheme, then the theme-choose-variant
> command will look for other available themes that belong to the same
> family in order to switch the themes.
>
>
> I didn't include background-mode because the code does nothing with that
> property, AFAICT.
>
>>>>>> +(defun theme-choose-variant (&optional no-confirm no-enable)
>>>>>> +  "Prompt to switch from the current theme to one of its a variants.
>>>>>
>>>>> I'd say: "Command to switch..."
>>>>
>>>> Do you think it is necessary to point out that it is a command?
>>>
>>> OK, maybe not.  But why start with "Prompt to"? It is likely that it
>>> will not prompt.  Why not get rid of it?
>>
>> Good point, so why not just
>>
>>      Switch from the current theme to one of its a variants.
>
> I think that's better, yes.  I think the "a" between "its" and
> "variants" is a typo.

Here is the updated patch:


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From 69c77d8f5de386e5024eeaad4a20dfd9afa71cd9 Mon Sep 17 00:00:00 2001
From: Philip Kaludercic <philipk@posteo.net>
Date: Sat, 17 Sep 2022 20:11:42 +0200
Subject: [PATCH] Tag themes with properties

* doc/emacs/custom.texi (Custom Themes): Document 'theme-choose-variant'.
* doc/lispref/customize.texi (Custom Themes): Document the new
optional argument to 'deftheme'.
(Autoload): Mention that 'deftheme' is not copied verbatim.
* etc/themes/adwaita-theme.el (adwaita): Add properties.
* etc/themes/deeper-blue-theme.el (deeper-blue): Add properties.
* etc/themes/dichromacy-theme.el (dichromacy): Add properties.
* etc/themes/light-blue-theme.el (light-blue): Add properties.
* etc/themes/manoj-dark-theme.el (manoj-dark): Add properties.
* etc/themes/misterioso-theme.el (misterioso): Add properties.
* etc/themes/tango-dark-theme.el (tango-dark): Add properties.
* etc/themes/tango-theme.el (tango): Add properties.
* etc/themes/tsdh-dark-theme.el (tsdh-dark): Add properties.
* etc/themes/tsdh-light-theme.el (tsdh-light): Add properties.
* etc/themes/wheatgrass-theme.el (wheatgrass): Add properties.
* etc/themes/whiteboard-theme.el (whiteboard): Add properties.
* etc/themes/wombat-theme.el (wombat): Add properties.
* etc/themes/modus-operandi-theme.el: Add properties.
* etc/themes/modus-vivendi-theme.el: Add properties.
* etc/themes/leuven-dark-theme.el (leuven-dark): Add properties.
* etc/themes/leuven-theme.el (leuven): Add properties.
* lisp/custom.el (deftheme): Allow for optional arguments to set the
property list.
(custom-declare-theme): Accept the same optional arguments as 'deftheme'.
(theme-list-variants): Add new function.
(theme-choose-variant): Add new command for switching between members
of a theme family.
(toggle-theme): Add an alias for 'theme-choose-variant'.
* lisp/emacs-lisp/loaddefs-gen.el (loaddefs-generate--make-autoload):
Handle 'defcustom's by extracting the properties.  (Bug#57639)
---
 doc/emacs/custom.texi              | 10 ++++
 doc/lispref/customize.texi         | 24 +++++++++-
 doc/lispref/loading.texi           |  2 +-
 etc/themes/adwaita-theme.el        |  5 +-
 etc/themes/deeper-blue-theme.el    |  5 +-
 etc/themes/dichromacy-theme.el     |  5 +-
 etc/themes/leuven-dark-theme.el    |  8 +++-
 etc/themes/leuven-theme.el         |  8 +++-
 etc/themes/light-blue-theme.el     |  5 +-
 etc/themes/manoj-dark-theme.el     |  5 +-
 etc/themes/misterioso-theme.el     |  5 +-
 etc/themes/modus-operandi-theme.el |  2 +
 etc/themes/modus-vivendi-theme.el  |  2 +
 etc/themes/tango-dark-theme.el     |  7 ++-
 etc/themes/tango-theme.el          |  6 ++-
 etc/themes/tsdh-dark-theme.el      |  6 ++-
 etc/themes/tsdh-light-theme.el     |  6 ++-
 etc/themes/wheatgrass-theme.el     |  5 +-
 etc/themes/whiteboard-theme.el     |  5 +-
 etc/themes/wombat-theme.el         |  5 +-
 lisp/custom.el                     | 73 +++++++++++++++++++++++++++---
 lisp/emacs-lisp/loaddefs-gen.el    |  6 +++
 22 files changed, 179 insertions(+), 26 deletions(-)

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index ff7ab83190..f98527bf9a 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -667,6 +667,16 @@ Custom Themes
 the @file{*Custom Themes*} buffer; or type @kbd{M-x describe-theme}
 anywhere in Emacs and enter the theme name.
 
+@findex theme-choose-variant
+Some themes have variants (most often just two: light and dark).  You
+can switch to another variant using @kbd{M-x theme-choose-variant}.
+If the currently active theme has only one other variant, it will be
+selected; if there are more variants, the command will prompt you
+which one to switch to.
+
+Note that @code{theme-choose-variant} only works if a single theme
+is active.
+
 @node Creating Custom Themes
 @subsection Creating Custom Themes
 @cindex custom themes, creating
diff --git a/doc/lispref/customize.texi b/doc/lispref/customize.texi
index 6ba35cffff..204719e942 100644
--- a/doc/lispref/customize.texi
+++ b/doc/lispref/customize.texi
@@ -1428,12 +1428,32 @@ Custom Themes
 be a call to @code{deftheme}, and the last form should be a call to
 @code{provide-theme}.
 
-@defmac deftheme theme &optional doc
+@defmac deftheme theme &optional doc &rest properties
 This macro declares @var{theme} (a symbol) as the name of a Custom
 theme.  The optional argument @var{doc} should be a string describing
 the theme; this is the description shown when the user invokes the
 @code{describe-theme} command or types @kbd{?} in the @samp{*Custom
-Themes*} buffer.
+Themes*} buffer.  The remaining arguments @var{properties} are used
+pass a property list with theme attributes.
+
+The following attributes are supported:
+
+@table @code
+@item :family
+A symbol designating what ``family'' a theme belongs to.  A
+@dfn{family} of themes is a set of similar themes that differ by minor
+aspects, such as face colors that are meant for the light vs dark
+background of the frame.
+@item :kind
+A symbol.  If a theme is enabled and this property has the value
+@code{color-scheme}, then the @code{theme-choose-variant} command will
+look for other available themes that belong to the same family in
+order to switch the themes.  Other values are currently unspecified
+and should not be used.
+@item :background-mode
+A symbol, either @code{light} or @code{dark}.  This attribute is
+currently unused, but should still be specified.
+@end table
 
 Two special theme names are disallowed (using them causes an error):
 @code{user} is a dummy theme that stores the user's direct
diff --git a/doc/lispref/loading.texi b/doc/lispref/loading.texi
index 4e4f12dc32..c7fbdac1d7 100644
--- a/doc/lispref/loading.texi
+++ b/doc/lispref/loading.texi
@@ -662,7 +662,7 @@ Autoload
 and @code{define-global-minor-mode}.
 
 @item Other definition types:
-@code{defcustom}, @code{defgroup}, @code{defclass}
+@code{defcustom}, @code{defgroup}, @code{deftheme}, @code{defclass}
 (@pxref{Top,EIEIO,,eieio,EIEIO}), and @code{define-skeleton}
 (@pxref{Top,Autotyping,,autotype,Autotyping}).
 @end table
diff --git a/etc/themes/adwaita-theme.el b/etc/themes/adwaita-theme.el
index ba83a0578c..6ad8405559 100644
--- a/etc/themes/adwaita-theme.el
+++ b/etc/themes/adwaita-theme.el
@@ -21,10 +21,13 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme adwaita
   "Face colors similar to the default theme of Gnome 3 (Adwaita).
 The colors are chosen to match Adwaita window decorations and the
-default look of the Gnome 3 desktop.")
+default look of the Gnome 3 desktop."
+  :background-mode 'light
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
   (custom-theme-set-faces
diff --git a/etc/themes/deeper-blue-theme.el b/etc/themes/deeper-blue-theme.el
index 8f19147f91..48ed9ba061 100644
--- a/etc/themes/deeper-blue-theme.el
+++ b/etc/themes/deeper-blue-theme.el
@@ -21,8 +21,11 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme deeper-blue
-  "Face colors using a deep blue background.")
+  "Face colors using a deep blue background."
+  :background-mode 'dark
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
   (custom-theme-set-faces
diff --git a/etc/themes/dichromacy-theme.el b/etc/themes/dichromacy-theme.el
index d53c075d92..fe44d520cc 100644
--- a/etc/themes/dichromacy-theme.el
+++ b/etc/themes/dichromacy-theme.el
@@ -21,6 +21,7 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme dichromacy
   "Face colors suitable for red/green color-blind users.
 The color palette is from B. Wong, Nature Methods 8, 441 (2011).
@@ -28,7 +29,9 @@ dichromacy
 differentiated by individuals with protanopia or deuteranopia.
 
 Basic, Font Lock, Isearch, Gnus, Message, Flyspell, and
-Ansi-Color faces are included.")
+Ansi-Color faces are included."
+  :background-mode 'light
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89)))
       (orange "#e69f00")
diff --git a/etc/themes/leuven-dark-theme.el b/etc/themes/leuven-dark-theme.el
index 0e162c8bab..08978a2668 100644
--- a/etc/themes/leuven-dark-theme.el
+++ b/etc/themes/leuven-dark-theme.el
@@ -5,7 +5,7 @@
 ;; Author: Fabrice Niessen <(concat "fniessen" at-sign "pirilampo.org")>
 ;; Contributor: Thibault Polge <(concat "thibault" at-sign "thb.lt")>
 ;; URL: https://github.com/fniessen/emacs-leuven-dark-theme
-;; Version: 20220202.1126
+;; Version: 20221010.1208
 ;; Keywords: color theme
 
 ;; This file is part of GNU Emacs.
@@ -93,11 +93,15 @@ leuven-dark-scale-font
 
 ;;; Theme Faces.
 
+;;;###theme-autoload
 (deftheme leuven-dark
   "Face colors with a light background.
 Basic, Font Lock, Isearch, Gnus, Message, Org mode, Diff, Ediff,
 Flyspell, Semantic, and Ansi-Color faces are included -- and much
-more...")
+more..."
+  :background-mode 'dark
+  :family 'leuven
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89)))
 
diff --git a/etc/themes/leuven-theme.el b/etc/themes/leuven-theme.el
index d9a8d5391a..e712a79adf 100644
--- a/etc/themes/leuven-theme.el
+++ b/etc/themes/leuven-theme.el
@@ -4,7 +4,7 @@
 
 ;; Author: Fabrice Niessen <(concat "fniessen" at-sign "pirilampo.org")>
 ;; URL: https://github.com/fniessen/emacs-leuven-theme
-;; Version: 20200513.1928
+;; Version: 20221010.1209
 ;; Keywords: color theme
 
 ;; This file is part of GNU Emacs.
@@ -74,11 +74,15 @@ leuven-scale-font
 
 ;;; Theme Faces.
 
+;;;###theme-autoload
 (deftheme leuven
   "Face colors with a light background.
 Basic, Font Lock, Isearch, Gnus, Message, Org mode, Diff, Ediff,
 Flyspell, Semantic, and Ansi-Color faces are included -- and much
-more...")
+more..."
+  :background-mode 'light
+  :kind 'color-scheme
+  :family 'leuven)
 
 (let ((class '((class color) (min-colors 89)))
 
diff --git a/etc/themes/light-blue-theme.el b/etc/themes/light-blue-theme.el
index eeca46210c..808fcbfeb2 100644
--- a/etc/themes/light-blue-theme.el
+++ b/etc/themes/light-blue-theme.el
@@ -26,8 +26,11 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme light-blue
-  "Face colors utilizing a light blue background.")
+  "Face colors utilizing a light blue background."
+  :background-mode 'light
+  :kind 'color-scheme)
 
 (make-obsolete 'light-blue nil "29.1")
 
diff --git a/etc/themes/manoj-dark-theme.el b/etc/themes/manoj-dark-theme.el
index af5576386c..f9aaa97c25 100644
--- a/etc/themes/manoj-dark-theme.el
+++ b/etc/themes/manoj-dark-theme.el
@@ -64,10 +64,13 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme manoj-dark
   "Very high contrast faces with a black background.
 This theme avoids subtle color variations, while avoiding the
-jarring angry fruit salad look to reduce eye fatigue.")
+jarring angry fruit salad look to reduce eye fatigue."
+  :background-mode 'dark
+  :kind 'color-scheme)
 
 (custom-theme-set-faces
  'manoj-dark
diff --git a/etc/themes/misterioso-theme.el b/etc/themes/misterioso-theme.el
index 55186384ad..3fd6cdb5af 100644
--- a/etc/themes/misterioso-theme.el
+++ b/etc/themes/misterioso-theme.el
@@ -21,8 +21,11 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme misterioso
-  "Predominantly blue/cyan faces on a dark cyan background.")
+  "Predominantly blue/cyan faces on a dark cyan background."
+  :background-mode 'dark
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
 
diff --git a/etc/themes/modus-operandi-theme.el b/etc/themes/modus-operandi-theme.el
index 6e609c0803..0f0630a6d1 100644
--- a/etc/themes/modus-operandi-theme.el
+++ b/etc/themes/modus-operandi-theme.el
@@ -71,4 +71,6 @@
 
   (provide-theme 'modus-operandi))
 
+;;;###theme-autoload (put 'modus-operandi 'theme-properties '(:background-mode light :kind color-scheme :family modus))
+
 ;;; modus-operandi-theme.el ends here
diff --git a/etc/themes/modus-vivendi-theme.el b/etc/themes/modus-vivendi-theme.el
index 0983e26c78..02c2d9e129 100644
--- a/etc/themes/modus-vivendi-theme.el
+++ b/etc/themes/modus-vivendi-theme.el
@@ -71,4 +71,6 @@
 
   (provide-theme 'modus-vivendi))
 
+;;;###theme-autoload (put 'modus-vivendi 'theme-properties '(:background-mode dark :kind color-scheme :family modus))
+
 ;;; modus-vivendi-theme.el ends here
diff --git a/etc/themes/tango-dark-theme.el b/etc/themes/tango-dark-theme.el
index ef00d2ac49..85995e4e99 100644
--- a/etc/themes/tango-dark-theme.el
+++ b/etc/themes/tango-dark-theme.el
@@ -27,10 +27,15 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme tango-dark
   "Face colors using the Tango palette (dark background).
 Basic, Font Lock, Isearch, Gnus, Message, Ediff, Flyspell,
-Semantic, and Ansi-Color faces are included.")
+Semantic, and Ansi-Color faces are included."
+  :background-mode 'dark
+  :kind 'color-scheme
+  :family 'tango)
+
 
 (let ((class '((class color) (min-colors 89)))
       ;; Tango palette colors.
diff --git a/etc/themes/tango-theme.el b/etc/themes/tango-theme.el
index ecbbf03753..2ac1b42294 100644
--- a/etc/themes/tango-theme.el
+++ b/etc/themes/tango-theme.el
@@ -27,10 +27,14 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme tango
   "Face colors using the Tango palette (light background).
 Basic, Font Lock, Isearch, Gnus, Message, Ediff, Flyspell,
-Semantic, and Ansi-Color faces are included.")
+Semantic, and Ansi-Color faces are included."
+  :background-mode 'light
+  :kind 'color-scheme
+  :family 'tango)
 
 (let ((class '((class color) (min-colors 89)))
       ;; Tango palette colors.
diff --git a/etc/themes/tsdh-dark-theme.el b/etc/themes/tsdh-dark-theme.el
index a88ad75520..6b1e865e42 100644
--- a/etc/themes/tsdh-dark-theme.el
+++ b/etc/themes/tsdh-dark-theme.el
@@ -19,8 +19,12 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme tsdh-dark
-  "A dark theme used and created by Tassilo Horn.")
+  "A dark theme used and created by Tassilo Horn."
+  :background-mode 'dark
+  :kind 'color-scheme
+  :family 'tsdh)
 
 (custom-theme-set-faces
  'tsdh-dark
diff --git a/etc/themes/tsdh-light-theme.el b/etc/themes/tsdh-light-theme.el
index d9d09b702b..ac964d66d6 100644
--- a/etc/themes/tsdh-light-theme.el
+++ b/etc/themes/tsdh-light-theme.el
@@ -19,9 +19,13 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme tsdh-light
   "A light Emacs theme.
-Used and created by Tassilo Horn.")
+Used and created by Tassilo Horn."
+  :background-mode 'light
+  :kind 'color-scheme
+  :family 'tsdh)
 
 (custom-theme-set-faces
  'tsdh-light
diff --git a/etc/themes/wheatgrass-theme.el b/etc/themes/wheatgrass-theme.el
index c56c8a2d8a..20e7bbbac2 100644
--- a/etc/themes/wheatgrass-theme.el
+++ b/etc/themes/wheatgrass-theme.el
@@ -19,11 +19,14 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme wheatgrass
   "High-contrast green/blue/brown faces on a black background.
 Basic, Font Lock, Isearch, Gnus, and Message faces are included.
 The default face foreground is wheat, with other faces in shades
-of green, brown, and blue.")
+of green, brown, and blue."
+  :background-mode 'dark
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
   (custom-theme-set-faces
diff --git a/etc/themes/whiteboard-theme.el b/etc/themes/whiteboard-theme.el
index f21b18b421..2f86234b32 100644
--- a/etc/themes/whiteboard-theme.el
+++ b/etc/themes/whiteboard-theme.el
@@ -21,8 +21,11 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme whiteboard
-  "Face colors similar to markers on a whiteboard.")
+  "Face colors similar to markers on a whiteboard."
+  :background-mode 'light
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
   (custom-theme-set-faces
diff --git a/etc/themes/wombat-theme.el b/etc/themes/wombat-theme.el
index d9fab8ac78..9bb026ead1 100644
--- a/etc/themes/wombat-theme.el
+++ b/etc/themes/wombat-theme.el
@@ -21,11 +21,14 @@
 
 ;;; Code:
 
+;;;###theme-autoload
 (deftheme wombat
   "Medium-contrast faces with a dark gray background.
 Adapted, with permission, from a Vim color scheme by Lars H. Nielsen.
 Basic, Font Lock, Isearch, Gnus, Message, and Ansi-Color faces
-are included.")
+are included."
+  :background-mode 'dark
+  :kind 'color-scheme)
 
 (let ((class '((class color) (min-colors 89))))
   (custom-theme-set-faces
diff --git a/lisp/custom.el b/lisp/custom.el
index 604b1a3ff4..0d3e2e5d0c 100644
--- a/lisp/custom.el
+++ b/lisp/custom.el
@@ -1152,9 +1152,11 @@ custom--sort-vars-1
 ;;   (provide-theme 'THEME)
 
 
-(defmacro deftheme (theme &optional doc)
+(defmacro deftheme (theme &optional doc &rest properties)
   "Declare THEME to be a Custom theme.
 The optional argument DOC is a doc string describing the theme.
+PROPERTIES are interpreted as a property list that will be stored
+in the `theme-properties' property for THEME.
 
 Any theme `foo' should be defined in a file called `foo-theme.el';
 see `custom-make-theme-feature' for more information."
@@ -1164,18 +1166,25 @@ deftheme
     ;; It is better not to use backquote in this file,
     ;; because that makes a bootstrapping problem
     ;; if you need to recompile all the Lisp files using interpreted code.
-    (list 'custom-declare-theme (list 'quote theme) (list 'quote feature) doc)))
+    (list 'custom-declare-theme (list 'quote theme) (list 'quote feature) doc
+          (cons 'list properties))))
 
-(defun custom-declare-theme (theme feature &optional doc)
+(defun custom-declare-theme (theme feature &optional doc properties)
   "Like `deftheme', but THEME is evaluated as a normal argument.
-FEATURE is the feature this theme provides.  Normally, this is a symbol
-created from THEME by `custom-make-theme-feature'."
+FEATURE is the feature this theme provides.  Normally, this is a
+symbol created from THEME by `custom-make-theme-feature'.  The
+optional argument DOC may contain the documentation for THEME.
+The optional argument PROPERTIES may contain a property list of
+attributes associated with THEME."
   (unless (custom-theme-name-valid-p theme)
     (error "Custom theme cannot be named %S" theme))
   (unless (memq theme custom-known-themes)
     (push theme custom-known-themes))
   (put theme 'theme-feature feature)
-  (when doc (put theme 'theme-documentation doc)))
+  (when doc
+    (put theme 'theme-documentation doc))
+  (when properties
+    (put theme 'theme-properties properties)))
 
 (defun custom-make-theme-feature (theme)
   "Given a symbol THEME, create a new symbol by appending \"-theme\".
@@ -1372,6 +1381,58 @@ load-theme
     (enable-theme theme))
   t)
 
+(defun theme-list-variants (theme &rest list)
+  "Return a list of theme variants for THEME.
+By default this will use all known custom themes (see
+`custom-available-themes') to check for variants.  This can be
+restricted if the optional argument LIST containing a list of
+theme symbols to consider."
+  (let* ((properties (get theme 'theme-properties))
+         (family (plist-get properties :family)))
+    (seq-filter
+     (lambda (variant)
+       (and (eq (plist-get (get variant 'theme-properties) :family)
+                family)
+            (not (eq variant theme))))
+     (or list (custom-available-themes)))))
+
+(defun theme-choose-variant (&optional no-confirm no-enable)
+  "Switch from the current theme to one of its variants.
+The current theme will be disabled before variant is enabled.  If
+the current theme has only one variant, switch to that variant
+without prompting, otherwise prompt for the variant to select.
+See `load-theme' for the meaning of NO-CONFIRM and NO-ENABLE."
+  (interactive)
+  (let ((active-color-schemes
+         (seq-filter
+          (lambda (theme)
+            ;; FIXME: As most themes currently do not have a `:kind'
+            ;; tag, it is assumed that a theme is a color scheme by
+            ;; default.  This should be reconsidered in the future.
+            (memq (plist-get (get theme 'theme-properties) :kind)
+                  '(color-scheme nil)))
+          custom-enabled-themes)))
+    (cond
+     ((length= active-color-schemes 0)
+      (user-error "No theme is active, cannot toggle"))
+     ((length> active-color-schemes 1)
+      (user-error "More than one theme active, cannot unambiguously toggle")))
+    (let* ((theme (car active-color-schemes))
+           (family (plist-get (get theme 'theme-properties) :family)))
+      (unless family
+        (error "Theme `%s' does not have any known variants" theme))
+      (let* ((variants (theme-list-variants theme))
+             (choice (cond
+                      ((null variants)
+                       (error "`%s' has no variants" theme))
+                      ((length= variants 1)
+                       (car variants))
+                      ((intern (completing-read "Load custom theme: " variants))))))
+        (disable-theme theme)
+        (load-theme choice no-confirm no-enable)))))
+
+(defalias 'toggle-theme #'theme-choose-variant)
+
 (defun custom-theme-load-confirm (hash)
   "Query the user about loading a Custom theme that may not be safe.
 The theme should be in the current buffer.  If the user agrees,
diff --git a/lisp/emacs-lisp/loaddefs-gen.el b/lisp/emacs-lisp/loaddefs-gen.el
index 964d23c770..d2654fb206 100644
--- a/lisp/emacs-lisp/loaddefs-gen.el
+++ b/lisp/emacs-lisp/loaddefs-gen.el
@@ -283,6 +283,12 @@ loaddefs-generate--make-autoload
            ,@(when-let ((safe (plist-get props :safe)))
                `((put ',varname 'safe-local-variable ,safe))))))
 
+     ;; Extract theme properties.
+     ((eq car 'deftheme)
+      (let* ((name (car-safe (cdr-safe form)))
+	     (props (nthcdr 3 form)))
+	`(put ',name 'theme-properties (list ,@props))))
+
      ((eq car 'defgroup)
       ;; In Emacs this is normally handled separately by cus-dep.el, but for
       ;; third party packages, it can be convenient to explicitly autoload
-- 
2.37.3