Throw an error when moving a directory into itself.

Fixes #1192

Author: tannewt

extmod/vfs_fat.c

@@ -237,7 +237,23 @@ STATIC mp_obj_t fat_vfs_rename(mp_obj_t vfs_in, mp_obj_t path_in, mp_obj_t path_
     mp_obj_fat_vfs_t *self = MP_OBJ_TO_PTR(vfs_in);
     const char *old_path = mp_obj_str_get_str(path_in);
     const char *new_path = mp_obj_str_get_str(path_out);
-    FRESULT res = f_rename(&self->fatfs, old_path, new_path);
+
+    // Check to see if we're moving a directory into itself. This occurs when we're moving a
+    // directory where the old path is a prefix of the new and the next character is a "/" and thus
+    // preserves the original directory name.
+    FILINFO fno;
+    FRESULT res = f_stat(&self->fatfs, old_path, &fno);
+    if (res != FR_OK) {
+        mp_raise_OSError(fresult_to_errno_table[res]);
+    }
+    if ((fno.fattrib & AM_DIR) != 0 &&
+            strlen(new_path) > strlen(old_path) &&
+            new_path[strlen(old_path)] == '/' &&
+            strncmp(old_path, new_path, strlen(old_path)) == 0) {
+        mp_raise_OSError(MP_EINVAL);
+    }
+
+    res = f_rename(&self->fatfs, old_path, new_path);
     if (res == FR_EXIST) {
         // if new_path exists then try removing it (but only if it's a file)
         fat_vfs_remove_internal(vfs_in, path_out, 0); // 0 == file attribute