Facilitate typing `C-SPC' on Android

* doc/emacs/android.texi (Android Windowing): Mention C-SPC
interception and how it may be disabled.

* java/org/gnu/emacs/EmacsNative.java (shouldForwardCtrlSpace):
New function.

* java/org/gnu/emacs/EmacsView.java (onKeyPreIme): New function.
If the provided key code is SPC and the event's modifier key
mask contains ControlMask, relay it directly to onKeyDown.

* java/org/gnu/emacs/EmacsWindow.java (eventModifiers): Export
and make static.

* src/android.c (shouldForwardCtrlSpace): New function.

* src/androidfns.c (syms_of_androidfns)
<android_intercept_control_space>: New defvar.

3 files changed, 25 insertions, 1 deletions

diff --git a/java/org/gnu/emacs/EmacsNative.java b/java/org/gnu/emacs/EmacsNative.java
index fae0ba98f86..a4b45aafbc1 100644
--- a/java/org/gnu/emacs/EmacsNative.java
+++ b/java/org/gnu/emacs/EmacsNative.java
@@ -196,6 +196,10 @@ public final class EmacsNative
      KEYCODE_VOLUME_MUTE should be forwarded to Emacs.  */
   public static native boolean shouldForwardMultimediaButtons ();
 
+  /* Return whether KEYCODE_SPACE combined with META_CTRL_MASK should
+     be prevented from reaching the system input method.  */
+  public static native boolean shouldForwardCtrlSpace ();
+
   /* Initialize the current thread, by blocking signals that do not
      interest it.  */
   public static native void setupSystemThread ();
diff --git a/java/org/gnu/emacs/EmacsView.java b/java/org/gnu/emacs/EmacsView.java
index 5a4bcbaa005..04c3d824027 100644
--- a/java/org/gnu/emacs/EmacsView.java
+++ b/java/org/gnu/emacs/EmacsView.java
@@ -472,6 +472,26 @@ public final class EmacsView extends ViewGroup
 
   @Override
   public boolean
+  onKeyPreIme (int keyCode, KeyEvent event)
+  {
+    /* Several Android systems intercept key events representing
+       C-SPC.  Avert this by detecting C-SPC events here and relaying
+       them directly to onKeyDown.
+
+       Make this optional though, since some input methods also
+       leverage C-SPC as a shortcut for switching languages.  */
+
+    if ((keyCode == KeyEvent.KEYCODE_SPACE
+         && (window.eventModifiers (event)
+             & KeyEvent.META_CTRL_MASK) != 0)
+        && !EmacsNative.shouldForwardCtrlSpace ())
+      return onKeyDown (keyCode, event);
+
+    return super.onKeyPreIme (keyCode, event);
+  }
+
+  @Override
+  public boolean
   onKeyDown (int keyCode, KeyEvent event)
   {
     if ((keyCode == KeyEvent.KEYCODE_VOLUME_UP
diff --git a/java/org/gnu/emacs/EmacsWindow.java b/java/org/gnu/emacs/EmacsWindow.java
index aff5046b22e..3738376a6f4 100644
--- a/java/org/gnu/emacs/EmacsWindow.java
+++ b/java/org/gnu/emacs/EmacsWindow.java
@@ -576,7 +576,7 @@ public final class EmacsWindow extends EmacsHandleObject
      input EVENT.  Replace bits corresponding to Left or Right keys
      with their corresponding general modifier bits.  */
 
-  private int
+  public static int
   eventModifiers (KeyEvent event)
   {
     int state;