Print a more helpful error message if manifest path is not writable

src/manifest.py

@@ -25,7 +25,7 @@
 import asyncio
 from enum import IntEnum
 import logging
-import os
+import errno, os, sys
 
 import aiohttp
 from lxml.etree import XMLSyntaxError
@@ -445,25 +445,38 @@ def get_outdated_external_data(self) -> t.List[ExternalBase]:
         ]
 
     def _update_manifest(self, path, datas, changes):
-        path_has_changes = False
-        for data in datas:
-            if data.new_version is None:
-                continue
+        try:
+            path_has_changes = False
+            for data in datas:
+                if data.new_version is None:
+                    continue
 
-            data.update()
-            if data.new_version.version is not None:
-                message = "Update {} to {}".format(
-                    data.filename, data.new_version.version
+                data.update()
+                if data.new_version.version is not None:
+                    message = "Update {} to {}".format(
+                        data.filename, data.new_version.version
+                    )
+                else:
+                    message = "Update {}".format(data.filename)
+
+                changes[message] = None
+                path_has_changes = True
+
+            if path_has_changes:
+                log.info("Updating %s", path)
+                self._dump_manifest(path)
+        except (IOError, OSError) as e:
+            if e.errno in (errno.EPERM, errno.EACCES, errno.EROFS):
+                log.error(
+                    "Please make sure the path is writable and has appropriate permissions"
                 )
+                if os.path.exists("/.flatpak-info"):
+                    log.error(
+                        "You are running inside a sandbox. Please make sure it has appropriate filesystem permissions"
+                    )
             else:
-                message = "Update {}".format(data.filename)
-
-            changes[message] = None
-            path_has_changes = True
-
-        if path_has_changes:
-            log.info("Updating %s", path)
-            self._dump_manifest(path)
+                log.error(e)
+            sys.exit(1)
 
     def _update_appdata(self):
         if not self.app_id: