Port `Precondition` to C++ (#1040)

* port FieldMask to C++

* address changes

* address changes

* fix test

* address change

* Port transform operations (FSTTransformOperation, FSTServerTimestampTransform) to C++

* address changes

* address changes

* address changes

* implement `FieldTransform` in C++

* port `FieldTransform`

* make `fieldTransforms` shared inside `context`

* Implement Precondition in C++ w/o test yet

* add unit test for `Precondition`

* port `Precondition`

* address changes

* address changes

* fix bugs for integration test

* address changes

* fix lint

* address changes

* address changes

1 files changed, 29 insertions, 0 deletions

diff --git a/Firestore/core/test/firebase/firestore/testutil/testutil.h b/Firestore/core/test/firebase/firestore/testutil/testutil.h
index 9c69784..9a875f4 100644
--- a/Firestore/core/test/firebase/firestore/testutil/testutil.h
+++ b/Firestore/core/test/firebase/firestore/testutil/testutil.h
@@ -17,9 +17,16 @@
 #ifndef FIRESTORE_CORE_TEST_FIREBASE_FIRESTORE_TESTUTIL_TESTUTIL_H_
 #define FIRESTORE_CORE_TEST_FIREBASE_FIRESTORE_TESTUTIL_TESTUTIL_H_
 
+#include <chrono>  // NOLINT(build/c++11)
+#include <cstdint>
+
+#include "Firestore/core/include/firebase/firestore/timestamp.h"
+#include "Firestore/core/src/firebase/firestore/model/document.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
+#include "Firestore/core/src/firebase/firestore/model/no_document.h"
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
+#include "Firestore/core/src/firebase/firestore/model/snapshot_version.h"
 #include "absl/strings/string_view.h"
 
 namespace firebase {
@@ -40,6 +47,28 @@ inline model::ResourcePath Resource(absl::string_view field) {
   return model::ResourcePath::FromString(field);
 }
 
+/**
+ * Creates a snapshot version from the given version timestamp.
+ *
+ * @param version a timestamp in microseconds since the epoch.
+ */
+inline model::SnapshotVersion Version(int64_t version) {
+  namespace chr = std::chrono;
+  auto timepoint =
+      chr::time_point<chr::system_clock>(chr::microseconds(version));
+  return model::SnapshotVersion{Timestamp::FromTimePoint(timepoint)};
+}
+
+inline model::Document Doc(absl::string_view key, int64_t version) {
+  return model::Document{model::FieldValue::ObjectValueFromMap({}), Key(key),
+                         Version(version),
+                         /* has_local_mutations= */ false};
+}
+
+inline model::NoDocument DeletedDoc(absl::string_view key, int64_t version) {
+  return model::NoDocument{Key(key), Version(version)};
+}
+
 // Add a non-inline function to make this library buildable.
 // TODO(zxu123): remove once there is non-inline function.
 void dummy();