For icon rules and emblems, use the standard theme names for the icons. Generalize the naming so 1 or both of the icons can have themed names.

src/calibre/gui2/library/alternate_views.py

@@ -64,6 +64,7 @@ from calibre.gui2 import clip_border_radius, config, empty_index, gprefs, rating
 from calibre.gui2.dnd import path_from_qurl
 from calibre.gui2.gestures import GestureManager
 from calibre.gui2.library.caches import CoverCache, ThumbnailCache
+from calibre.gui2.library.models import themed_icon_name
 from calibre.gui2.pin_columns import PinContainer
 from calibre.utils import join_with_timeout
 from calibre.utils.config import prefs, tweaks
@@ -555,11 +556,9 @@ class CoverDelegate(QStyledItemDelegate):
             ans = QIcon.ic('ok.png').pixmap(sz, sz)
         elif name:
             pmap = None
-            if is_dark_theme():
-                n,ext = os.path.splitext(name)
-                d = os.path.join(config_dir, 'cc_icons', n + '-dark' + ext)
-                if os.path.exists(d):
-                    pmap = QIcon(d).pixmap(sz, sz)
+            d = themed_icon_name(os.path.join(config_dir, 'cc_icons'), name)
+            if d is not None:
+                pmap = QIcon(d).pixmap(sz, sz)
             if pmap is None:
                 pmap = QIcon(os.path.join(config_dir, 'cc_icons', name)).pixmap(sz, sz)
             if not pmap.isNull():

src/calibre/gui2/library/models.py

@@ -93,6 +93,20 @@ class ColumnColor:  # {{{
 # }}}
 
 
+def themed_icon_name(icon_dir, icon_name):
+    root,ext = os.path.splitext(icon_name)
+    # Remove any theme from the icon name
+    root = root.removesuffix('-for-dark-theme').removesuffix('-for-light-theme')
+    # Check if the correct themed icon exists.
+    theme_suffix = '-for-dark-theme' if is_dark_theme() else '-for-light-theme'
+    d = os.path.join(icon_dir, root + theme_suffix + ext)
+    if os.path.exists(d):
+        return d
+    # No themed icon exists. Try the original name
+    d = os.path.join(icon_dir, icon_name)
+    return d if os.path.exists(d) else None
+
+
 class ColumnIcon:  # {{{
 
     def __init__(self, formatter, model):
@@ -134,14 +148,8 @@ class ColumnIcon:  # {{{
                 dim = int(self.dpr * rh)
                 icon_dir = os.path.join(config_dir, 'cc_icons')
                 for icon in icons:
-                    d = None
-                    if is_dark_theme():
-                        root,ext = os.path.splitext(icon)
-                        d = os.path.join(icon_dir, root + '-dark' + ext)
-                        d = d if os.path.exists(d) else None
-                    if d is None:
-                        d = os.path.join(icon_dir, icon)
-                    if (os.path.exists(d)):
+                    d = themed_icon_name(icon_dir, icon)
+                    if d is not None:
                         bm = QPixmap(d)
                         scaled, nw, nh = fit_image(bm.width(), bm.height(), bm.width(), dim)
                         bm = bm.scaled(int(nw), int(nh), aspectRatioMode=Qt.AspectRatioMode.IgnoreAspectRatio,

src/calibre/gui2/preferences/coloring.py

@@ -568,15 +568,22 @@ class RuleEditor(QDialog):  # {{{
     def show_theme_help(self):
         msg = '<p>'+ _(
             'You can use different icons in light and dark themes. To do this, '
-            'add two icons to the icon list. The light theme icon will have '
-            'the "normal" name, for example "ok.png". The dark theme icon must '
-            'have the same name with "-dark" appended. For example, if the light '
-            'theme icon is named "ok.png" then the dark theme icon must be named '
-            '"ok-dark.png".'
+            'add two icons to the icon list. One of the icons must have either the '
+            '"plain" name, for example "ok.png", or the themed name, for example '
+            '"ok-for-light-theme.png". The other icon must have a themed name with '
+            'the same prefix, for example "ok-for-dark-theme.png". '
             '</p><p>'
-            'When defining a rule, always use the "normal" name. The -dark icon will be '
-            'automatically substituted for the normal icon when a dark theme is '
-            'being used.'
+            'Example: if the light theme icon is named "ok.png" then the dark '
+            'theme icon must be named "ok-for-dark-theme.png". If the light '
+            'theme icon is named "ok-for-light-theme.png" then the dark theme '
+            'icon must be named either ok.png or "ok-for-dark-theme.png".'
+            '</p><p>'
+            'When defining a rule, use either of the icon names. The correct '
+            'icon for the theme will automatically be used, if it exists.'
+            '</p><p>'
+            'You are not required to change existing rules to use theming. Decide '
+            'the theme where the existing icon should be used then add the '
+            'other icon with the correct themed name. '
             '</p><p>'
             'Remember to add both the light and dark theme icons to the list of icons.'
         ) + '</p>'