Support `toolkit-theme-set-functions' on Android and execute hooks safely

* java/org/gnu/emacs/EmacsNative.java (setEmacsParams): New arg
UIMODE.
(sendConfigurationChanged): New args DETAIL and UI_MODE.

* java/org/gnu/emacs/EmacsNoninteractive.java (main1): Provide
an undefined UI mode.

* java/org/gnu/emacs/EmacsService.java (EmacsService): New field
uiMode.
(onCreate): Initialize this field at start-up and provide the
same to setEmacsParams.
(onConfigurationChanged): If the UI mode has been altered,
generate a configuration changed event to match.

* src/android.c (android_ui_mode): New variable.
(setEmacsParams): New argument UI_MODE.  Initialize the same
from this variable.

* src/androidgui.h (enum android_configuration_changed): New
enum.
(struct android_configuration_changed_event): New field
`DETAIL'.  Convert fields providing specifics into a union of
display density information and a UI mode integer.

* src/androidterm.c (handle_one_android_event): Handle both
manners of configuration change events.
(android_term_init): Initialize Vtoolkit_theme from UI mode
provided at start-up.

* src/frame.c (syms_of_frame): Always define Vtoolkit_theme.
Define Qtoolkit_theme_set_functions.

* src/gtkutil.c (xg_update_dark_mode_for_all_displays):

* src/w32term.c (w32_read_socket): Generate special toolkit
theme events, rather than executing hooks directly within the
read_socket callback.

* src/keyboard.c (kbd_buffer_get_event)
<TOOLKIT_THEME_CHANGED_EVENT>: Run Qtoolkit_theme_set_functions
and set Vtoolkit_theme from event->ie.arg.

* src/termhooks.h (enum event_kind): New event
TOOLKIT_THEME_CHANGED_EVENT.

etc/NEWS

@@ -3573,10 +3573,10 @@ automatically toggling between them.
 
 ---
 *** 'toolkit-theme-set-functions' called when the toolkit theme is set for Emacs.
-When the theme is set on PGTK or MS-Windows builds,
+When the theme is set on PGTK, Android, or MS-Windows systems,
 'toolkit-theme-set-functions' is called.  The result is stored in the
 variable 'toolkit-theme' as either symbol 'dark' or 'light', but may be
-expanded to future toolkit-specific symbols in the future.
+extended to encompass other toolkit-specific symbols in the future.
 
 
 * Changes in Emacs 31.1 on Non-Free Operating Systems

java/org/gnu/emacs/EmacsNative.java

@@ -61,6 +61,9 @@ public final class EmacsNative
      scaledDensity is the DPI value used to translate point sizes to
      pixel sizes when loading fonts.
 
+     uiMode holds the bits of the system's UI mode specification
+     defining the active system theme.
+
      classPath must be the classpath of this app_process process, or
      NULL.
 
@@ -74,6 +77,7 @@ public final class EmacsNative
 					    float pixelDensityX,
 					    float pixelDensityY,
 					    float scaledDensity,
+					    int uiMode,
 					    String classPath,
 					    EmacsService emacsService,
 					    int apiLevel);
@@ -197,8 +201,9 @@ public final class EmacsNative
   public static native void sendNotificationAction (String tag, String action);
 
   /* Send an ANDROID_CONFIGURATION_CHANGED event.  */
-  public static native void sendConfigurationChanged (float dpiX, float dpiY,
-						      float dpiScaled);
+  public static native void sendConfigurationChanged (int detail, float dpiX,
+						      float dpiY, float dpiScaled,
+						      int ui_mode);
 
   /* Return the file name associated with the specified file
      descriptor, or NULL if there is none.  */

java/org/gnu/emacs/EmacsNoninteractive.java

@@ -67,7 +67,7 @@ public final class EmacsNoninteractive
     cacheDir = context.getCacheDir ().getCanonicalPath ();
     EmacsNative.setEmacsParams (assets, filesDir,
 				libDir, cacheDir, 0.0f,
-				0.0f, 0.0f, null, null,
+				0.0f, 0.0f, 0x0, null, null,
 				Build.VERSION.SDK_INT);
 
     /* Now find the dump file that Emacs should use, if it has already

java/org/gnu/emacs/EmacsService.java

@@ -150,6 +150,10 @@ public final class EmacsService extends Service
      consulted for font scaling.  */
   private double dpiX, dpiY, dpiScaled;
 
+  /* The display's previously observed UI mode as it relates to the
+     system theme.  */
+  private int uiMode;
+
   static
   {
     servicingQuery = new AtomicInteger ();
@@ -240,6 +244,7 @@ public final class EmacsService extends Service
     float tempScaledDensity;
     Resources resources;
     DisplayMetrics metrics;
+    Configuration configuration;
 
     super.onCreate ();
 
@@ -254,6 +259,8 @@ public final class EmacsService extends Service
     tempScaledDensity = ((getScaledDensity (metrics)
 			  / metrics.density)
 			 * pixelDensityX);
+    configuration = resources.getConfiguration ();
+    uiMode = configuration.uiMode & Configuration.UI_MODE_NIGHT_MASK;
     resolver = getContentResolver ();
     mainThread = Thread.currentThread ();
 
@@ -311,7 +318,8 @@ public final class EmacsService extends Service
 	      EmacsNative.setEmacsParams (manager, filesDir, libDir,
 					  cacheDir, pixelDensityX,
 					  pixelDensityY, scaledDensity,
-					  classPath, EmacsService.this,
+					  uiMode, classPath,
+					  EmacsService.this,
 					  Build.VERSION.SDK_INT);
 	    }
 	  }, extraStartupArguments);
@@ -375,8 +383,14 @@ public final class EmacsService extends Service
 	dpiX = pixelDensityX;
 	dpiY = pixelDensityY;
 	dpiScaled = scaledDensity;
-	EmacsNative.sendConfigurationChanged (pixelDensityX, pixelDensityY,
-					      scaledDensity);
+	EmacsNative.sendConfigurationChanged (0, pixelDensityX, pixelDensityY,
+					      scaledDensity, 0);
+      }
+
+    if ((newConfig.uiMode & Configuration.UI_MODE_NIGHT_MASK) != uiMode)
+      {
+	uiMode = newConfig.uiMode & Configuration.UI_MODE_NIGHT_MASK;
+	EmacsNative.sendConfigurationChanged (1, 0.0f, 0.0f, 0.0f, uiMode);
       }
 
     super.onConfigurationChanged (newConfig);

src/android.c

@@ -163,6 +163,9 @@ double android_pixel_density_x, android_pixel_density_y;
    font sizes.  */
 double android_scaled_pixel_density;
 
+/* The display's current UI mode.  */
+int android_ui_mode;
+
 /* The Android application data directory.  */
 static char *android_files_dir;
 
@@ -1476,6 +1479,7 @@ NATIVE_NAME (setEmacsParams) (JNIEnv *env, jobject object,
 			      jfloat pixel_density_x,
 			      jfloat pixel_density_y,
 			      jfloat scaled_density,
+			      jint ui_mode,
 			      jobject class_path,
 			      jobject emacs_service_object,
 			      jint api_level)
@@ -1501,6 +1505,7 @@ NATIVE_NAME (setEmacsParams) (JNIEnv *env, jobject object,
   android_pixel_density_x = pixel_density_x;
   android_pixel_density_y = pixel_density_y;
   android_scaled_pixel_density = scaled_density;
+  android_ui_mode = ui_mode;
 
   __android_log_print (ANDROID_LOG_INFO, __func__,
 		       "Initializing "PACKAGE_STRING"...\nPlease report bugs to "
@@ -2821,8 +2826,9 @@ NATIVE_NAME (sendNotificationAction) (JNIEnv *env, jobject object,
 
 JNIEXPORT jlong JNICALL
 NATIVE_NAME (sendConfigurationChanged) (JNIEnv *env, jobject object,
-					jfloat dpi_x, jfloat dpi_y,
-					jfloat dpi_scaled)
+					int detail, jfloat dpi_x,
+					jfloat dpi_y, jfloat dpi_scaled,
+					int ui_mode)
 {
   JNI_STACK_ALIGNMENT_PROLOGUE;
 
@@ -2831,9 +2837,24 @@ NATIVE_NAME (sendConfigurationChanged) (JNIEnv *env, jobject object,
   event.config.type = ANDROID_CONFIGURATION_CHANGED;
   event.config.serial = ++event_serial;
   event.config.window = ANDROID_NONE;
-  event.config.dpi_x = dpi_x;
-  event.config.dpi_y = dpi_y;
-  event.config.dpi_scaled = dpi_scaled;
+  event.config.detail = detail;
+
+  switch (detail)
+    {
+    case ANDROID_PIXEL_DENSITY_CHANGED:
+      event.config.u.pixel_density.dpi_x = dpi_x;
+      event.config.u.pixel_density.dpi_y = dpi_y;
+      event.config.u.pixel_density.dpi_scaled = dpi_scaled;
+      break;
+
+    case ANDROID_UI_MODE_CHANGED:
+      event.config.u.ui_mode = ui_mode;
+      break;
+
+    default:
+      emacs_abort ();
+    }
+
   android_write_event (&event);
   return event_serial;
 }

src/android.h

@@ -102,6 +102,7 @@ extern ssize_t android_readlinkat (int, const char *restrict, char *restrict,
 
 extern double android_pixel_density_x, android_pixel_density_y;
 extern double android_scaled_pixel_density;
+extern int android_ui_mode;
 
 static_assert (sizeof (android_handle) == sizeof (jobject));
 #define android_resolve_handle(handle) ((jobject) (handle))

src/androidgui.h

@@ -596,6 +596,17 @@ struct android_notification_event
   size_t length;
 };
 
+enum android_configuration_change_type
+  {
+    ANDROID_PIXEL_DENSITY_CHANGED,
+    ANDROID_UI_MODE_CHANGED,
+  };
+
+#define UI_MODE_NIGHT_MASK	0x00000030
+#define UI_MODE_NIGHT_NO	0x00000010
+#define UI_MODE_NIGHT_YES	0x00000020
+#define UI_MODE_NIGHT_UNDEFINED 0x00000000
+
 struct android_configuration_changed_event
 {
   /* Type of the event.  */
@@ -607,13 +618,23 @@ struct android_configuration_changed_event
   /* The window that gave rise to the event (None).  */
   android_window window;
 
+  /* What type of change this event represents.  */
+  enum android_configuration_change_type detail;
+
+  union {
+    struct {
       /* The density of the display along the horizontal and vertical
 	 axes.  */
       double dpi_x, dpi_y;
 
-  /* The density to take into account when converting between point and
-     pixel dimensions.  */
+      /* The density to take into account when converting between point
+	 and pixel dimensions.  */
       double dpi_scaled;
+    } pixel_density;
+
+    /* A change in the reported user interface UI mode.  */
+    int ui_mode;
+  } u;
 };
 
 union android_event

src/androidterm.c

@@ -1825,11 +1825,15 @@ handle_one_android_event (struct android_display_info *dpyinfo,
       goto OTHER;
 
     case ANDROID_CONFIGURATION_CHANGED:
+
+      if (event->config.detail == ANDROID_PIXEL_DENSITY_CHANGED)
+	{
 	  /* Update the display configuration from the event.  */
-      dpyinfo->resx = event->config.dpi_x;
-      dpyinfo->resy = event->config.dpi_y;
-      dpyinfo->font_resolution = event->config.dpi_scaled;
-#ifdef notdef
+	  dpyinfo->resx = event->config.u.pixel_density.dpi_x;
+	  dpyinfo->resy = event->config.u.pixel_density.dpi_y;
+	  dpyinfo->font_resolution
+	    = event->config.u.pixel_density.dpi_scaled;
+#if notdef
 	  __android_log_print (ANDROID_LOG_VERBOSE, __func__,
 			       "New display configuration: "
 			       "resx = %.2f resy = %.2f font_resolution = %.2f",
@@ -1838,6 +1842,15 @@ handle_one_android_event (struct android_display_info *dpyinfo,
 	  inev.ie.kind = CONFIG_CHANGED_EVENT;
 	  inev.ie.frame_or_window = XCAR (dpyinfo->name_list_element);
 	  inev.ie.arg = Qfont_render;
+	}
+      else if (event->config.detail == ANDROID_UI_MODE_CHANGED)
+	{
+	  android_ui_mode = event->config.u.ui_mode;
+	  inev.ie.kind = TOOLKIT_THEME_CHANGED_EVENT;
+	  inev.ie.arg = (android_ui_mode == UI_MODE_NIGHT_YES
+			 ? Qdark : Qlight);
+	}
+
       goto OTHER;
 
     default:
@@ -6753,6 +6766,8 @@ android_term_init (void)
   dpyinfo->resx = android_pixel_density_x;
   dpyinfo->resy = android_pixel_density_y;
   dpyinfo->font_resolution = android_scaled_pixel_density;
+  Vtoolkit_theme = (android_ui_mode == UI_MODE_NIGHT_YES
+		    ? Qdark : Qlight);
 #endif /* !ANDROID_STUBIFY */
 
   /* https://lists.gnu.org/r/emacs-devel/2015-11/msg00194.html  */

src/frame.c

@@ -7619,16 +7619,15 @@ The default is \\+`inhibit' in NS builds and nil everywhere else.  */);
 #endif /* !HAVE_EXT_TOOL_BAR || USE_GTK */
 #endif /* HAVE_WINDOW_SYSTEM */
 
-#if (defined(HAVE_PGTK) && defined(HAVE_GSETTINGS)) || defined (WINDOWSNT)
   DEFVAR_LISP ("toolkit-theme", Vtoolkit_theme,
                doc: /* The current toolkit theme.
 Either the symbol `light' or the symbol `dark', reflecting the system's
 current theme preference.  This variable is updated automatically when
 the system theme changes.
 
-This variable is only available on PGTK and MS-Windows builds.  */);
+This variable is only set on PGTK, Android, and MS-Windows builds.  */);
   Vtoolkit_theme = Qnil;
   DEFSYM (Qlight, "light");
   DEFSYM (Qdark, "dark");
-#endif
+  DEFSYM (Qtoolkit_theme_set_functions, "toolkit-theme-set-functions");
 }

src/gtkutil.c

@@ -1476,14 +1476,12 @@ xg_update_dark_mode_for_all_displays (bool dark_mode_p)
        xg_set_gtk_theme_dark_mode (dark_mode_p, settings);
      }
 
-   Vtoolkit_theme = dark_mode_p ? Qdark : Qlight;
-   Lisp_Object hook = intern ("toolkit-theme-set-functions");
-   if (!NILP (Fboundp (hook)))
    {
-       Lisp_Object args[2];
-       args[0] = hook;
-       args[1] = Vtoolkit_theme;
-       Frun_hook_with_args (2, args);
+     struct input_event inev;
+     EVENT_INIT (inev);
+     inev.kind = TOOLKIT_THEME_CHANGED_EVENT;
+     inev.arg = msg.msg.wParam ? Qdark : Qlight;
+     kbd_buffer_store_event (&inev);
    }
 }
 

src/keyboard.c

@@ -4242,6 +4242,15 @@ kbd_buffer_get_event (KBOARD **kbp,
 	}
 #endif /* HAVE_ANDROID */
 
+      case TOOLKIT_THEME_CHANGED_EVENT:
+	kbd_fetch_ptr = next_kbd_event (event);
+	input_pending = readable_events (0);
+
+	Vtoolkit_theme = event->ie.arg;
+	CALLN (Frun_hook_with_args, Qtoolkit_theme_set_functions,
+	       event->ie.arg);
+	break;
+
 #ifdef HAVE_EXT_MENU_BAR
       case MENU_BAR_ACTIVATE_EVENT:
 	{

src/termhooks.h

@@ -341,6 +341,10 @@ enum event_kind
      which the monitors changed.  */
   , MONITORS_CHANGED_EVENT
 
+  /* In a TOOLKIT_THEME_CHANGED_EVENT, .arg is the value to which the
+     toolkit theme was altered.  */
+  , TOOLKIT_THEME_CHANGED_EVENT
+
 #ifdef HAVE_HAIKU
   /* In a NOTIFICATION_CLICKED_EVENT, .arg is an integer identifying
      the notification that was clicked.  */

src/w32term.c

@@ -6085,15 +6085,8 @@ w32_read_socket (struct terminal *terminal,
 
 	case WM_EMACS_SET_TOOLKIT_THEME:
 	  {
-	    Vtoolkit_theme = msg.msg.wParam ? Qdark : Qlight;
-	    Lisp_Object hook = intern ("toolkit-theme-set-functions");
-	    if (!NILP (Fboundp (hook)))
-	      {
-		Lisp_Object args[2];
-		args[0] = hook;
-		args[1] = Vtoolkit_theme;
-		Frun_hook_with_args (2, args);
-	      }
+	    inev.kind = TOOLKIT_THEME_CHANGED_EVENT;
+	    inev.arg = msg.msg.wParam ? Qdark : Qlight;
 	  }
 	  break;