Port FieldTransform to C++ (#1033)

* 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`

* address changes

* fix lint

* address changes

2 files changed, 11 insertions, 7 deletions

diff --git a/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm b/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
index 17191f8..c0e9cad 100644
--- a/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
+++ b/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
@@ -23,6 +23,8 @@
 #import <GRPCClient/GRPCCall.h>
 #import <XCTest/XCTest.h>
 
+#include <vector>
+
 #import "Firestore/Protos/objc/firestore/local/MaybeDocument.pbobjc.h"
 #import "Firestore/Protos/objc/firestore/local/Mutation.pbobjc.h"
 #import "Firestore/Protos/objc/google/firestore/v1beta1/Common.pbobjc.h"
@@ -47,6 +49,7 @@
 
 #include "Firestore/core/src/firebase/firestore/model/database_id.h"
 #include "Firestore/core/src/firebase/firestore/model/field_mask.h"
+#include "Firestore/core/src/firebase/firestore/model/field_transform.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
 #include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
 
@@ -54,6 +57,7 @@ namespace testutil = firebase::firestore::testutil;
 namespace util = firebase::firestore::util;
 using firebase::firestore::model::DatabaseId;
 using firebase::firestore::model::FieldMask;
+using firebase::firestore::model::FieldTransform;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -67,7 +71,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (GCFSDocumentMask *)encodedFieldMask:(const FieldMask &)fieldMask;
 - (NSMutableArray<GCFSDocumentTransform_FieldTransform *> *)encodedFieldTransforms:
-    (NSArray<FSTFieldTransform *> *)fieldTransforms;
+    (const std::vector<FieldTransform> &)fieldTransforms;
 
 - (GCFSStructuredQuery_Filter *)encodedRelationFilter:(FSTRelationFilter *)filter;
 @end
diff --git a/Firestore/Example/Tests/Util/FSTHelpers.mm b/Firestore/Example/Tests/Util/FSTHelpers.mm
index 8f170e6..2e1082e 100644
--- a/Firestore/Example/Tests/Util/FSTHelpers.mm
+++ b/Firestore/Example/Tests/Util/FSTHelpers.mm
@@ -46,6 +46,7 @@
 #include "Firestore/core/src/firebase/firestore/model/database_id.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 #include "Firestore/core/src/firebase/firestore/model/field_mask.h"
+#include "Firestore/core/src/firebase/firestore/model/field_transform.h"
 #include "Firestore/core/src/firebase/firestore/model/field_value.h"
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
 #include "Firestore/core/src/firebase/firestore/model/transform_operations.h"
@@ -59,6 +60,7 @@ using firebase::firestore::model::DatabaseId;
 using firebase::firestore::model::DocumentKey;
 using firebase::firestore::model::FieldMask;
 using firebase::firestore::model::FieldPath;
+using firebase::firestore::model::FieldTransform;
 using firebase::firestore::model::FieldValue;
 using firebase::firestore::model::ResourcePath;
 using firebase::firestore::model::ServerTimestampTransform;
@@ -279,15 +281,13 @@ FSTPatchMutation *FSTTestPatchMutation(const absl::string_view path,
 FSTTransformMutation *FSTTestTransformMutation(NSString *path,
                                                NSArray<NSString *> *serverTimestampFields) {
   FSTDocumentKey *key = [FSTDocumentKey keyWithPath:testutil::Resource(util::MakeStringView(path))];
-  NSMutableArray<FSTFieldTransform *> *fieldTransforms = [NSMutableArray array];
+  std::vector<FieldTransform> fieldTransforms;
   for (NSString *field in serverTimestampFields) {
-    const FieldPath fieldPath = testutil::Field(util::MakeStringView(field));
+    FieldPath fieldPath = testutil::Field(util::MakeStringView(field));
     auto transformOp = absl::make_unique<ServerTimestampTransform>(ServerTimestampTransform::Get());
-    FSTFieldTransform *transform =
-        [[FSTFieldTransform alloc] initWithPath:fieldPath transform:std::move(transformOp)];
-    [fieldTransforms addObject:transform];
+    fieldTransforms.emplace_back(std::move(fieldPath), std::move(transformOp));
   }
-  return [[FSTTransformMutation alloc] initWithKey:key fieldTransforms:fieldTransforms];
+  return [[FSTTransformMutation alloc] initWithKey:key fieldTransforms:std::move(fieldTransforms)];
 }
 
 FSTDeleteMutation *FSTTestDeleteMutation(NSString *path) {