MB-39292: Allow a forced collection update to reset the manifest uid

The following cases of update are currently invalid and will be enabled
by force in this commit.

* Update where the manifest UID goes backwards
* Update where the manifest UID is equal
* Update where the manifest UID goes forwards, but makes no change

With this commit when a manifest is pushed to KV with force=true
any detectable changes will be applied. Detectable changes currently
only means when scope/collections are added or dropped.

In the case of a UID change, but no changes to collections this propagates
to VB::Manifest as a UID only change.

Change-Id: I1962ffe04f1fe6b46aab80b54410247444cc8483
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/140557
Tested-by: Build Bot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>

engines/ep/src/collections/manager.cc

@@ -299,8 +299,9 @@ bool Collections::Manager::warmupLoadManifest(const std::string& dbpath) {
     if (rv.has_value()) {
         EP_LOG_INFO(
                 "Collections::Manager::warmupLoadManifest: starting at "
-                "uid:{:#x}",
-                rv.value().getUid());
+                "uid:{:#x} force:{}",
+                rv.value().getUid(),
+                rv.value().isForcedUpdate());
         *currentManifest.wlock() = std::move(rv.value());
         return true;
     }

engines/ep/src/collections/manifest.cc

@@ -233,6 +233,25 @@ Manifest::Manifest(std::string_view json)
     }
 }
 
+Manifest::Manifest(Manifest&& other) {
+    *this = std::move(other);
+}
+
+Manifest& Manifest::operator=(Manifest&& other) {
+    if (*this != other) {
+        defaultCollectionExists = other.defaultCollectionExists;
+        scopes = std::move(other.scopes);
+        collections = std::move(other.collections);
+        if (other.force) {
+            uid.reset(other.uid);
+        } else {
+            uid = other.uid;
+        }
+        force = other.force;
+    }
+    return *this;
+}
+
 void Manifest::buildCollectionIdToEntryMap() {
     for (auto& scope : this->scopes) {
         for (auto& collection : scope.second.collections) {

engines/ep/src/collections/manifest.h

@@ -84,6 +84,12 @@ class Manifest {
     struct FlatBuffers {};
     explicit Manifest(std::string_view flatbufferData, FlatBuffers tag);
 
+    Manifest(Manifest&&);
+    /**
+     * Assignment operator that is aware of a forced assign (so uid can go back)
+     */
+    Manifest& operator=(Manifest&& other);
+
     bool doesDefaultCollectionExist() const {
         return defaultCollectionExists;
     }