From 9a6f2be2b67e4b96e57dd9476e053d0d7fc07265 Mon Sep 17 00:00:00 2001
From: Damien Elmes <gpg@ankiweb.net>
Date: Wed, 30 Oct 2019 10:17:09 +1000
Subject: [PATCH] force a full sync when fields or templates changed without
 schema mod

This is not an ideal solution and will not catch repositioned fields
or templates, but is at least an improvement over the previous behaviour.

https://github.com/dae/anki/pull/349#issuecomment-547236285
---
 anki/sync.py | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/anki/sync.py b/anki/sync.py
index f5d21e89d..c3ce9baf2 100644
--- a/anki/sync.py
+++ b/anki/sync.py
@@ -22,6 +22,9 @@ HTTP_TIMEOUT = 90
 HTTP_PROXY = None
 HTTP_BUF_SIZE = 64*1024
 
+class UnexpectedSchemaChange(Exception):
+    pass
+
 # Incremental syncing
 ##########################################################################
 
@@ -95,7 +98,11 @@ class Syncer:
         # ...and small objects
         lchg = self.changes()
         rchg = self.server.applyChanges(changes=lchg)
-        self.mergeChanges(lchg, rchg)
+        try:
+            self.mergeChanges(lchg, rchg)
+        except UnexpectedSchemaChange:
+            self.server.abort()
+            return self._forceFullSync()
         # step 3: stream large tables from server
         runHook("sync", "server")
         while 1:
@@ -119,17 +126,20 @@ class Syncer:
         c = self.sanityCheck()
         ret = self.server.sanityCheck2(client=c)
         if ret['status'] != "ok":
-            # roll back and force full sync
-            self.col.rollback()
-            self.col.modSchema(False)
-            self.col.save()
-            return "sanityCheckFailed"
+            return self._forceFullSync()
         # finalize
         runHook("sync", "finalize")
         mod = self.server.finish()
         self.finish(mod)
         return "success"
 
+    def _forceFullSync(self):
+        # roll back and force full sync
+        self.col.rollback()
+        self.col.modSchema(False)
+        self.col.save()
+        return "sanityCheckFailed"
+
     def _gravesChunk(self, graves):
         lim = 250
         chunk = dict(notes=[], cards=[], decks=[])
@@ -330,6 +340,14 @@ from notes where %s""" % d)
             l = self.col.models.get(r['id'])
             # if missing locally or server is newer, update
             if not l or r['mod'] > l['mod']:
+                # This is a hack to detect when the note type has been altered
+                # in an import without a full sync being forced. A future
+                # syncing algorithm should handle this in a better way.
+                if l:
+                    if len(l['flds']) != len(r['flds']):
+                        raise UnexpectedSchemaChange()
+                    if len(l['tmpls']) != len(r['tmpls']):
+                        raise UnexpectedSchemaChange()
                 self.col.models.update(r)
 
     # Decks