Avoid overwriting local changes with remote modifications.

The case we ran into is the following:
* Fetching the full payload and marking all messages of a thread as read
happens simultaneously.
* The local modification to mark as read gets immediately overwritten
when the full payload arrives.
* Eventually the modification gets replayed to the server though (and
the reversal isn't because coming from the source), so on next sync the
situation fixes itself.

To be able to improve this we try to protect local modifications in that
properties that have been modified since baseRevision (which currently
isn't, but should be equal to the last to the server replayed revision)
are not overwritten. This conflict resolution strategy thus always
prefers local modifications. baseRevision is currently set to the
current maximum revision of the store at the time when the resource
creates the modification.

1 files changed, 13 insertions, 1 deletions

diff --git a/common/pipeline.cpp b/common/pipeline.cpp
index 4afe9f3..cbdc91d 100644
--- a/common/pipeline.cpp
+++ b/common/pipeline.cpp
@@ -258,7 +258,19 @@ KAsync::Job<qint64> Pipeline::modifiedEntity(void const *command, size_t size)
         return KAsync::error<qint64>(0);
     }
 
-    auto newEntity = d->entityStore.applyDiff(bufferType, current, diff, deletions);
+    //We avoid overwriting local changes that haven't been played back yet with remote modifications
+    QSet<QByteArray> excludeProperties;
+    if (!replayToSource) { //We assume this means the change is coming from the source already
+        d->entityStore.readRevisions(bufferType, diff.identifier(), baseRevision, [&] (const QByteArray &uid, qint64 revision, const Sink::EntityBuffer &entity) {
+            if (entity.metadataBuffer()) {
+                if (auto metadata = GetMetadata(entity.metadataBuffer())) {
+                    excludeProperties += BufferUtils::fromVector(*metadata->modifiedProperties()).toSet();
+                }
+            }
+        });
+    }
+
+    auto newEntity = d->entityStore.applyDiff(bufferType, current, diff, deletions, excludeProperties);
 
     bool isMove = false;
     if (modifyEntity->targetResource()) {