Offer to grant storage permissions if absent

* java/org/gnu/emacs/EmacsService.java (externalStorageAvailable)
(requestStorageAccess23, requestStorageAccess30)
(requestStorageAccess): New functions.

* lisp/startup.el (fancy-startup-tail, normal-splash-screen):
Call android-win functions for inserting the new storage
permission notice.

* lisp/term/android-win.el
(android-display-storage-permission-popup)
(android-after-splash-screen): New functions.

* src/android.c (android_init_emacs_service): Link to new Java
functions.
(android_external_storage_available_p)
(android_request_storage_access): New functions.

* src/android.h: Update prototypes.

* src/androidfns.c (Fandroid_external_storage_available_p)
(Fandroid_request_storage_access): New functions.
(syms_of_androidfns): Register new subrs.

1 files changed, 55 insertions, 0 deletions

diff --git a/src/android.c b/src/android.c
index e116426ca05..7ca5eab817c 100644
--- a/src/android.c
+++ b/src/android.c
@@ -1628,6 +1628,10 @@ android_init_emacs_service (void)
                "Ljava/lang/String;)Ljava/lang/String;");
   FIND_METHOD (valid_authority, "validAuthority",
                "(Ljava/lang/String;)Z");
+  FIND_METHOD (external_storage_available,
+               "externalStorageAvailable", "()Z");
+  FIND_METHOD (request_storage_access,
+               "requestStorageAccess", "()V");
 #undef FIND_METHOD
 }
 
@@ -6558,6 +6562,57 @@ android_request_directory_access (void)
   return rc;
 }
 
+/* Return whether Emacs is entitled to access external storage.
+
+   On Android 5.1 and earlier, such permissions as are declared within
+   an application's manifest are granted during installation and are
+   irrevocable.
+
+   On Android 6.0 through Android 10.0, the right to read external
+   storage is a regular permission granted from the Permissions
+   panel.
+
+   On Android 11.0 and later, that right must be granted through an
+   independent ``Special App Access'' settings panel.  */
+
+bool
+android_external_storage_available_p (void)
+{
+  jboolean rc;
+  jmethodID method;
+
+  if (android_api_level <= 22) /* LOLLIPOP_MR1 */
+    return true;
+
+  method = service_class.external_storage_available;
+  rc = (*android_java_env)->CallNonvirtualBooleanMethod (android_java_env,
+                                                         emacs_service,
+                                                         service_class.class,
+                                                         method);
+  android_exception_check ();
+
+  return rc;
+}
+
+/* Display a dialog from which the aforementioned rights can be
+   granted.  */
+
+void
+android_request_storage_access (void)
+{
+  jmethodID method;
+
+  if (android_api_level <= 22) /* LOLLIPOP_MR1 */
+    return;
+
+  method = service_class.request_storage_access;
+  (*android_java_env)->CallNonvirtualVoidMethod (android_java_env,
+                                                 emacs_service,
+                                                 service_class.class,
+                                                 method);
+  android_exception_check ();
+}
+
 
 
 /* The thread from which a query against a thread is currently being