Allow starting Emacs --debug-init on Android

* doc/emacs/android.texi (Android Troubleshooting): Document
`debug-init' option.
* java/AndroidManifest.xml.in
(EmacsLauncherPreferencesActivity): New activity.  Export on
systems older than Android 7.0.
* java/org/gnu/emacs/EmacsActivity.java (onCreate): Adjust for
string startup argument.
* java/org/gnu/emacs/EmacsLauncherPreferencesActivity.java: New
file.
* java/org/gnu/emacs/EmacsPreferencesActivity.java
(EmacsPreferencesActivity): Don't make final.
(startEmacsQ): Give start-up argument as an argument, not as a
boolean.
(startEmacsDebugInit): New function.
(onCreate): Register new listener; make final.
* java/org/gnu/emacs/EmacsService.java (onCreate): Pass
extraStartupArgument.
* java/org/gnu/emacs/EmacsThread.java (EmacsThread): Rename
startDashQ to extraStartupArgument.
(run): Adjust accordingly.
* java/res/values-v24/bool.xml:
* java/res/values/bool.xml:
* java/res/values/strings.xml: New files.
* java/res/xml/preferences.xml: Add new option.  Move string
resources around.

11 files changed, 171 insertions, 26 deletions

diff --git a/java/AndroidManifest.xml.in b/java/AndroidManifest.xml.in
index f7f834e7582..082c4c9373e 100644
--- a/java/AndroidManifest.xml.in
+++ b/java/AndroidManifest.xml.in
@@ -180,6 +180,23 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
       </intent-filter>
     </activity>
 
+    <!-- Android 6 and earlier don't display ``application
+         preferences'' activities in Settings, so display the
+         preferences activity as a launcher icon instead.  -->
+
+    <activity android:autoRemoveFromRecents="true"
+              android:label="Emacs options"
+              android:enabled="@bool/isBeforeNougat"
+              android:exported="@bool/isBeforeNougat"
+              android:icon="@drawable/emacs_wrench"
+              android:name=".EmacsLauncherPreferencesActivity">
+      <intent-filter>
+        <action android:name="android.intent.action.MAIN" />
+        <category android:name="android.intent.category.DEFAULT" />
+        <category android:name="android.intent.category.LAUNCHER" />
+      </intent-filter>
+    </activity>
+
     <provider android:name="org.gnu.emacs.EmacsDocumentsProvider"
               android:authorities="org.gnu.emacs"
               android:exported="true"
diff --git a/java/org/gnu/emacs/EmacsActivity.java b/java/org/gnu/emacs/EmacsActivity.java
index b480fc40b2e..7ba268ba42d 100644
--- a/java/org/gnu/emacs/EmacsActivity.java
+++ b/java/org/gnu/emacs/EmacsActivity.java
@@ -193,11 +193,11 @@ public class EmacsActivity extends Activity
     ViewTreeObserver observer;
     int matchParent;
 
-    /* See if Emacs should be started with -Q.  */
+    /* See if Emacs should be started with any extra arguments, such
+       as `--quick'.  */
     intent = getIntent ();
-    EmacsService.needDashQ
-      = intent.getBooleanExtra ("org.gnu.emacs.START_DASH_Q",
-                                false);
+    EmacsService.extraStartupArgument
+      = intent.getStringExtra ("org.gnu.emacs.STARTUP_ARGUMENT");
 
     matchParent = FrameLayout.LayoutParams.MATCH_PARENT;
     params
diff --git a/java/org/gnu/emacs/EmacsLauncherPreferencesActivity.java b/java/org/gnu/emacs/EmacsLauncherPreferencesActivity.java
new file mode 100644
index 00000000000..1e1e5d97631
--- /dev/null
+++ b/java/org/gnu/emacs/EmacsLauncherPreferencesActivity.java
@@ -0,0 +1,31 @@
+/* Communication module for Android terminals.  -*- c-file-style: "GNU" -*-
+
+Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
+
+package org.gnu.emacs;
+
+/* This class only exists because EmacsPreferencesActivity is already
+   defined as an activity, the system wants a new class in order to
+   define a new activity, and only activities can be enabled or
+   disabled per the API level of the host.  */
+
+public final class EmacsLauncherPreferencesActivity
+  extends EmacsPreferencesActivity
+{
+
+}
diff --git a/java/org/gnu/emacs/EmacsPreferencesActivity.java b/java/org/gnu/emacs/EmacsPreferencesActivity.java
index 70934fa4bd4..7e67cc3679b 100644
--- a/java/org/gnu/emacs/EmacsPreferencesActivity.java
+++ b/java/org/gnu/emacs/EmacsPreferencesActivity.java
@@ -42,10 +42,11 @@ import android.preference.*;
    Unfortunately, there is no alternative that looks the same way.  */
 
 @SuppressWarnings ("deprecation")
-public final class EmacsPreferencesActivity extends PreferenceActivity
+public class EmacsPreferencesActivity extends PreferenceActivity
 {
-  /* Restart Emacs with -Q.  Call EmacsThread.exit to kill Emacs now, and
-     tell the system to EmacsActivity with some parameters later.  */
+  /* Restart Emacs with -Q.  Call EmacsThread.exit to kill Emacs now,
+     and tell the system to start EmacsActivity with some parameters
+     later.  */
 
   private void
   startEmacsQ ()
@@ -55,7 +56,24 @@ public final class EmacsPreferencesActivity extends PreferenceActivity
     intent = new Intent (this, EmacsActivity.class);
     intent.addFlags (Intent.FLAG_ACTIVITY_NEW_TASK
                      | Intent.FLAG_ACTIVITY_CLEAR_TASK);
-    intent.putExtra ("org.gnu.emacs.START_DASH_Q", true);
+    intent.putExtra ("org.gnu.emacs.STARTUP_ARGUMENT", "--quick");
+    startActivity (intent);
+    System.exit (0);
+  }
+
+  /* Restart Emacs with `--debug-init'.  Call EmacsThread.exit to kill
+     Emacs now, and tell the system to EmacsActivity with some
+     parameters later.  */
+
+  private void
+  startEmacsDebugInit ()
+  {
+    Intent intent;
+
+    intent = new Intent (this, EmacsActivity.class);
+    intent.addFlags (Intent.FLAG_ACTIVITY_NEW_TASK
+                     | Intent.FLAG_ACTIVITY_CLEAR_TASK);
+    intent.putExtra ("org.gnu.emacs.STARTUP_ARGUMENT", "--debug-init");
     startActivity (intent);
     System.exit (0);
   }
@@ -89,7 +107,7 @@ public final class EmacsPreferencesActivity extends PreferenceActivity
   }
 
   @Override
-  public void
+  public final void
   onCreate (Bundle savedInstanceState)
   {
     Preference tem;
@@ -111,7 +129,6 @@ public final class EmacsPreferencesActivity extends PreferenceActivity
        items.  */
 
     tem = findPreference ("start_quick");
-
     listener = new Preference.OnPreferenceClickListener () {
         @Override
         public boolean
@@ -123,9 +140,19 @@ public final class EmacsPreferencesActivity extends PreferenceActivity
       };
 
     tem.setOnPreferenceClickListener (listener);
+    tem = findPreference ("start_debug_init");
+    listener = new Preference.OnPreferenceClickListener () {
+        @Override
+        public boolean
+        onPreferenceClick (Preference preference)
+        {
+          startEmacsDebugInit ();
+          return true;
+        }
+      };
 
+    tem.setOnPreferenceClickListener (listener);
     tem = findPreference ("erase_dump");
-
     listener = new Preference.OnPreferenceClickListener () {
         @Override
         public boolean
diff --git a/java/org/gnu/emacs/EmacsService.java b/java/org/gnu/emacs/EmacsService.java
index 30ef71540a9..bb17d27bcf8 100644
--- a/java/org/gnu/emacs/EmacsService.java
+++ b/java/org/gnu/emacs/EmacsService.java
@@ -79,7 +79,10 @@ public final class EmacsService extends Service
 {
   public static final String TAG = "EmacsService";
   public static volatile EmacsService SERVICE;
-  public static boolean needDashQ;
+
+  /* If non-NULL, an extra argument to pass to
+     `android_emacs_init'.  */
+  public static String extraStartupArgument;
 
   private EmacsThread thread;
   private Handler handler;
@@ -231,7 +234,7 @@ public final class EmacsService extends Service
                                           (float) pixelDensityY,
                                           classPath, EmacsService.this);
             }
-          }, needDashQ,
+          }, extraStartupArgument,
           /* If any file needs to be opened, open it now.  */
           EmacsOpenActivity.fileToOpen);
         thread.start ();
diff --git a/java/org/gnu/emacs/EmacsThread.java b/java/org/gnu/emacs/EmacsThread.java
index d175fe332b5..468c6530af0 100644
--- a/java/org/gnu/emacs/EmacsThread.java
+++ b/java/org/gnu/emacs/EmacsThread.java
@@ -29,8 +29,9 @@ public class EmacsThread extends Thread
 {
   private static final String TAG = "EmacsThread";
 
-  /* Whether or not Emacs should be started -Q.  */
-  private boolean startDashQ;
+  /* Whether or not Emacs should be started with an additional
+     argument, and that additional argument if non-NULL.  */
+  private String extraStartupArgument;
 
   /* Runnable run to initialize Emacs.  */
   private Runnable paramsClosure;
@@ -40,10 +41,10 @@ public class EmacsThread extends Thread
 
   public
   EmacsThread (EmacsService service, Runnable paramsClosure,
-               boolean startDashQ, String fileToOpen)
+               String extraStartupArgument, String fileToOpen)
   {
     super ("Emacs main thread");
-    this.startDashQ = startDashQ;
+    this.extraStartupArgument = extraStartupArgument;
     this.paramsClosure = paramsClosure;
     this.fileToOpen = fileToOpen;
   }
@@ -56,18 +57,20 @@ public class EmacsThread extends Thread
 
     if (fileToOpen == null)
       {
-        if (!startDashQ)
+        if (extraStartupArgument == null)
           args = new String[] { "libandroid-emacs.so", };
         else
-          args = new String[] { "libandroid-emacs.so", "-Q", };
+          args = new String[] { "libandroid-emacs.so",
+                                extraStartupArgument, };
       }
     else
       {
-        if (!startDashQ)
+        if (extraStartupArgument != null)
           args = new String[] { "libandroid-emacs.so",
                                 fileToOpen, };
         else
-          args = new String[] { "libandroid-emacs.so", "-Q",
+          args = new String[] { "libandroid-emacs.so",
+                                extraStartupArgument,
                                 fileToOpen, };
       }
 
diff --git a/java/res/drawable/emacs_wrench.png b/java/res/drawable/emacs_wrench.png
new file mode 100644
index 00000000000..50572d3bed1
--- /dev/null
+++ b/java/res/drawable/emacs_wrench.png
diff --git a/java/res/values-v24/bool.xml b/java/res/values-v24/bool.xml
new file mode 100644
index 00000000000..37f07992995
--- /dev/null
+++ b/java/res/values-v24/bool.xml
@@ -0,0 +1,22 @@
+<!-- Boolean resources for GNU Emacs on Android.
+
+Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
+
+<resources>
+  <bool name="isBeforeNougat">false</bool>
+</resources>
diff --git a/java/res/values/bool.xml b/java/res/values/bool.xml
index d37eab745c0..2b253824e29 100644
--- a/java/res/values/bool.xml
+++ b/java/res/values/bool.xml
@@ -19,4 +19,5 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
 
 <resources>
   <bool name="isAtLeastKitKat">false</bool>
+  <bool name="isBeforeNougat">true</bool>
 </resources>
diff --git a/java/res/values/strings.xml b/java/res/values/strings.xml
new file mode 100644
index 00000000000..36a47be6c84
--- /dev/null
+++ b/java/res/values/strings.xml
@@ -0,0 +1,39 @@
+<!-- String resources used by GNU Emacs on Android.
+
+Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
+
+<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
+  <string name="start_quick_title">
+    Restart Emacs with -Q
+  </string>
+  <string name="start_quick_caption">
+    Restart Emacs, but do not load site lisp or init files.
+  </string>
+  <string name="start_debug_init_title">
+    Restart Emacs with --debug-init
+  </string>
+  <string name="start_debug_init_caption">
+    Restart Emacs, and display the debugger should an error occur while loading initialization files.
+  </string>
+  <string name="erase_dump_title">
+    Delete dump file
+  </string>
+  <string name="erase_dump_caption">
+    Remove the dumped state created when Emacs was installed.
+  </string>
+</resources>
diff --git a/java/res/xml/preferences.xml b/java/res/xml/preferences.xml
index f0c3abb52e7..d52d28816e5 100644
--- a/java/res/xml/preferences.xml
+++ b/java/res/xml/preferences.xml
@@ -19,10 +19,12 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
 
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <Preference android:key="start_quick"
-                android:title="Restart Emacs with -Q"
-                android:summary="Restart Emacs, but do not load site lisp or init files."/>
-
+                android:title="@string/start_quick_title"
+                android:summary="@string/start_quick_caption"/>
+    <Preference android:key="start_debug_init"
+                android:title="@string/start_debug_init_title"
+                android:summary="@string/start_debug_init_caption"/>
     <Preference android:key="erase_dump"
-                android:title="Delete dump file"
-                android:summary="Remove the dumped state created when Emacs was installed"/>
+                android:title="@string/erase_dump_title"
+                android:summary="@string/erase_dump_caption"/>
 </PreferenceScreen>