Fix visiting and saving writable content provider files

* java/org/gnu/emacs/EmacsService.java (checkContentUri):
Improve debug output.
* lisp/files.el (basic-save-buffer): Check whether or not file
itself exists before checking for the existence of the directory
containing it.
* src/android.c (android_open): Don't forget to set errno after
open_content_uri fails.

java/org/gnu/emacs/EmacsService.java

@@ -752,6 +752,8 @@ invocation of app_process (through android-emacs) can
     if (writable)
       mode += "w";
 
+    Log.d (TAG, "checkContentUri: checking against mode " + mode);
+
     try
       {
 	fd = resolver.openFileDescriptor (Uri.parse (name), mode);

lisp/files.el

@@ -5726,9 +5726,14 @@ Before and after saving the buffer, this function runs
 	          (run-hook-with-args-until-success 'write-file-functions)
 	          ;; If a hook returned t, file is already "written".
 	          ;; Otherwise, write it the usual way now.
-	          (let ((dir (file-name-directory
+	          (let ((file (buffer-file-name))
+                        (dir (file-name-directory
 			      (expand-file-name buffer-file-name))))
-		    (unless (file-exists-p dir)
+                    ;; Some systems have directories (like /content on
+                    ;; Android) in which files can exist without a
+                    ;; corresponding parent directory.
+		    (unless (or (file-exists-p file)
+                                (file-exists-p dir))
 		      (if (y-or-n-p
 		           (format-message
                             "Directory `%s' does not exist; create? " dir))

src/android.c

@@ -1715,9 +1715,19 @@ android_open (const char *filename, int oflag, int mode)
 	  return -1;
 	}
 
+      /* If fd is -1, just assume that the file does not exist,
+	 and return -1 with errno set to ENOENT.  */
+
+      if (fd == -1)
+	{
+	  errno = ENOENT;
+	  goto skip;
+	}
+
       if (mode & O_CLOEXEC)
 	android_close_on_exec (fd);
 
+    skip:
       ANDROID_DELETE_LOCAL_REF (string);
       return fd;
     }