synchroniser : raise error instead of returning a value

Raise a FatalSyncError when the synchronisation fails instead of
returning the unison return code.

src/unisync/synchroniser.py

@@ -16,7 +16,7 @@ import logging
 from pathlib import Path
 from typing import cast
 
-from unisync.errors import RemoteMountedError, InvalidMountError, UnknownSSHError
+from unisync.errors import RemoteMountedError, InvalidMountError, UnknownSSHError, FatalSyncError
 from unisync.config import BackupConfig
 
 logger = logging.getLogger(__name__)
@@ -105,9 +105,6 @@ class Synchroniser:
             connection_timeout:
                 Time given to the user to authenticate to the remote server.
                 On slow connections one might want to increase this.
-        Returns:
-            An error code (0 success, 1 TimeoutExpired, 2 KeyboardInterrupt).
-            TODO change that to raising the exception.
 
         Raises:
             subprocess.TimeoutExpired:
@@ -156,18 +153,18 @@ class Synchroniser:
         close = subprocess.Popen(command)
         return close.wait()
 
-    def sync_files(self, paths:list, force:bool=False) -> int:
+    def sync_files(self, paths:list, force:bool=False) -> None:
         """Synchronises the files.
 
         Args:
             paths: List of paths to synchronise.
             force: Force the changes from remote to local.
 
-        Returns:
-            The return code of sync.
+        Raises:
+            FatalSyncError: A fatal error occured during the synchronisation.
         """
 
-        return self.sync(
+        self.sync(
                 f"ssh://{self.remote_user}@{self.remote_ip}/{self.remote_dir}/.data",
                 self.local,
                 paths=paths,
@@ -175,16 +172,16 @@ class Synchroniser:
                 other=self.files_extra
                 )
 
-    def sync_links(self, ignore:list) -> int:
+    def sync_links(self, ignore:list) -> None:
         """Synchronises the links, they must exist already.
 
         Args:
             ignore: List of paths to ignore.
 
-        Returns:
-            The return code of sync.
+        Raises:
+            FatalSyncError: A fatal error occured during the synchronisation.
         """
-        return self.sync(
+        self.sync(
                 f"ssh://{self.remote_user}@{self.remote_ip}/{self.remote_dir}/links",
                 self.local,
                 ignore=ignore,
@@ -194,7 +191,7 @@ class Synchroniser:
     def sync(self, remote_root:str, local_root:str,
              paths:list=[], ignore:list=[], force:bool=False,
              other:list=[]
-             ) -> int:
+             ) -> None:
         """Performs the synchronisation by calling unison.
 
         Args:
@@ -213,8 +210,11 @@ class Synchroniser:
                 They will be added to the command as is no - in front.
                 For exemple backups are implemented using this argument.
 
-        Returns:
-            the unison return code see section 6.11 of the documentation
+        Raises:
+            FatalSyncError:
+                If unison returns 3 it means either a fatal error occured or the synchronisation
+                was interrupted.
+                If this happens propagate the error to unisync.
         """
         command = [ "/usr/bin/unison", "-root", remote_root, "-root", local_root ]
         for arg in self.args_bool:
@@ -247,7 +247,8 @@ class Synchroniser:
 
         proc = subprocess.Popen(command)
         ret_code = proc.wait()
-        return ret_code
+        if ret_code == 3:
+            raise FatalSyncError("Synchronisation could not be completed")
 
     def update_links(self, background:bool=True):
         """Updates the links on the remote.