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

[Philip Kaludercic]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: 57639@debbugs.gnu.org
>> From: Philip Kaludercic <philipk@posteo.net>
>> Date: Sat, 17 Sep 2022 18:13:39 +0000
>> 
>> +@findex theme-choose-variant
>> +  Some themes have variants (most often these are light and dark
>> +pairs).  You can switch between these by typing @kbd{M-x
>> +theme-choose-variant}.  Note that this only works if only one theme is
>> +active.  If a theme has only one alternative, it will toggle
>> +automatically.  If there are more of them, it will query which one to
>> +use.
>
> This description is confusing, I needed to read it several times
> before I understood what you were trying to say.  The main problem is
> that the "Note" sentence doesn't belong, and it interrupts the logic
> of the description.  Here's my suggestion for saying it more clearly:
>
>   Some themes have variants (most often just two: light and dark).
>   You can switch to another variant with @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.

I prefer your phrasing and have adapted it in my next iteration of the
patch below.

> (Btw, what happens if more than one theme is active and the user
> invokes theme-choose-variant? should this be described?)

The current patch doesn't support this, but I've considered that a
custom theme could clarify that it is a colour scheme in the new property
list, and toggling would then not assume that there is only one active
theme but only one active colour scheme.

>> +Themes*} buffer.  The remaining arguments @var{properties} is used
>> +pass a property list with theme attributes.                ^^^^^^^
>
> "are used", in plural.

Fixed.

>> +  :brightness 'light
>
> Should we use :background-mode instead of :brightness, for consistency
> with frame-background-mode?

I chose "brightness" because I was looking at terms used in colour
theory and everyday language[0], and considered describing properties
such as "hue", "saturation", "contrast", etc. but that would probably be
overkill.  Consistency is probably preferable, so I'll also make this change.

[0] https://en.wikipedia.org/wiki/Color_term#In_natural_languages

>> +(defun theme-choose-variant (&optional no-confirm no-enable)
>> +  "Toggle the current active theme by enabling its dual pair.
>
> "Toggle ... by enabling"?  "Dual pair"?  Can this sentence be
> rephrased to be more clear?

>> +The current theme will be immediately disabled before the dual
>> +theme has been enabled.
>
> Likewise here: "dual theme" doesn't explain itself, and seems to be
> inaccurate, given the description in the manual.

You are right, the documentation was outdated.  See below.

>>                          If THEME is not active an error will be
>> +raised.
>
> Passive tense alert!
>
>>           If theme is nil For NO-CONFIRM and NO-ENABLE, see
>> +`load-theme'."
>
> Something's missing here or wrong with the punctuation?

The sentence was cut-off, so I just removed everything from "It" to
"nil".

>> +   ((length> custom-enabled-themes 1)
>> +    (user-error "More than one theme active, cannot unambiguously toggle")))
>
> Wouldn't it be better to prompt for the theme in this case?

That would be another possibility.  I guess it could be combined with
the above proposal.

>> +  (let* ((theme (car custom-enabled-themes))
>> +         (family (plist-get (get theme 'theme-properties) :family)))
>> +    (unless family
>> +      (error "`%s' is not part of a family" theme))
>
> "Family"? this terminology was never mentioned in the manual or the
> doc string.  How about
>
>   Theme `%s' does not have any variants
>
> instead?

Strictly speaking that error message would be wrong at this point,
because we cannot say if a theme has no variants if it is not part of a
family.  This is because variants of a theme are all those that are part
of the same family.  I think it would be better to clarify this in the
documentation.

> Thanks.

>From ae4f1596c479b9703c27b3635cff88f89a0b730a 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'.
* etc/themes/leuven-dark-theme.el (leuven-dark): Add properties.
* etc/themes/leuven-theme.el (leuven): 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.
* 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'.
---
 doc/emacs/custom.texi           | 11 ++++++
 doc/lispref/customize.texi      |  5 +--
 etc/themes/leuven-dark-theme.el |  6 ++--
 etc/themes/leuven-theme.el      |  6 ++--
 etc/themes/tango-dark-theme.el  |  4 ++-
 etc/themes/tango-theme.el       |  4 ++-
 etc/themes/tsdh-dark-theme.el   |  4 ++-
 etc/themes/tsdh-light-theme.el  |  4 ++-
 lisp/custom.el                  | 62 +++++++++++++++++++++++++++++----
 9 files changed, 90 insertions(+), 16 deletions(-)

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index ff7ab83190..4d5a674564 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -667,6 +667,17 @@ 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).  In
+this case we say the theme is part of a family of themes.  You can
+switch to another variant within a family 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..911b6c4d75 100644
--- a/doc/lispref/customize.texi
+++ b/doc/lispref/customize.texi
@@ -1428,12 +1428,13 @@ 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.
 
 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/etc/themes/leuven-dark-theme.el b/etc/themes/leuven-dark-theme.el
index 0e162c8bab..42ebd7b2d6 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: 20220917.2332
 ;; Keywords: color theme
 
 ;; This file is part of GNU Emacs.
@@ -97,7 +97,9 @@ 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)
 
 (let ((class '((class color) (min-colors 89)))
 
diff --git a/etc/themes/leuven-theme.el b/etc/themes/leuven-theme.el
index d9a8d5391a..07c34e944c 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: 20220917.2332
 ;; Keywords: color theme
 
 ;; This file is part of GNU Emacs.
@@ -78,7 +78,9 @@ 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
+  :family 'leuven)
 
 (let ((class '((class color) (min-colors 89)))
 
diff --git a/etc/themes/tango-dark-theme.el b/etc/themes/tango-dark-theme.el
index ef00d2ac49..fb5a1b29eb 100644
--- a/etc/themes/tango-dark-theme.el
+++ b/etc/themes/tango-dark-theme.el
@@ -30,7 +30,9 @@
 (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
+  :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..026718bf38 100644
--- a/etc/themes/tango-theme.el
+++ b/etc/themes/tango-theme.el
@@ -30,7 +30,9 @@
 (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
+  :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..ddd710a16e 100644
--- a/etc/themes/tsdh-dark-theme.el
+++ b/etc/themes/tsdh-dark-theme.el
@@ -20,7 +20,9 @@
 ;;; Code:
 
 (deftheme tsdh-dark
-  "A dark theme used and created by Tassilo Horn.")
+  "A dark theme used and created by Tassilo Horn."
+  :background-mode 'dark
+  :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..724b081880 100644
--- a/etc/themes/tsdh-light-theme.el
+++ b/etc/themes/tsdh-light-theme.el
@@ -21,7 +21,9 @@
 
 (deftheme tsdh-light
   "A light Emacs theme.
-Used and created by Tassilo Horn.")
+Used and created by Tassilo Horn."
+  :background-mode 'light
+  :family 'tsdh)
 
 (custom-theme-set-faces
  'tsdh-light
diff --git a/lisp/custom.el b/lisp/custom.el
index 352b5b0e16..f04241ca4d 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 +1381,47 @@ load-theme
     (enable-theme theme))
   t)
 
+(defun theme-list-variants (theme &rest list)
+  "Return a list of theme variants for THEME.
+If the optional argument LIST is not given, "
+  (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)
+  "Prompt to switch from the current theme to a variant.
+Themes only have variants if they are part of a family of themes.
+The current theme will be immediately disabled before variant is
+enabled.  In case the current theme has only one variant, it will
+be toggled without prompting.  For NO-CONFIRM and NO-ENABLE, see
+`load-theme'."
+  (interactive)
+  (cond
+   ((length= custom-enabled-themes 0)
+    (user-error "No theme is active, cannot toggle"))
+   ((length> custom-enabled-themes 1)
+    (user-error "More than one theme active, cannot unambiguously toggle")))
+  (let* ((theme (car custom-enabled-themes))
+         (family (plist-get (get theme 'theme-properties) :family)))
+    (unless family
+      (error "`%s' is not part of a family" 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,
-- 
2.37.3