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

5 files changed, 28 insertions, 19 deletions

diff --git a/Firestore/Example/Tests/Integration/FSTDatastoreTests.mm b/Firestore/Example/Tests/Integration/FSTDatastoreTests.mm
index 430366f..ad911ce 100644
--- a/Firestore/Example/Tests/Integration/FSTDatastoreTests.mm
+++ b/Firestore/Example/Tests/Integration/FSTDatastoreTests.mm
@@ -42,12 +42,14 @@
 #include "Firestore/core/src/firebase/firestore/auth/empty_credentials_provider.h"
 #include "Firestore/core/src/firebase/firestore/core/database_info.h"
 #include "Firestore/core/src/firebase/firestore/model/database_id.h"
+#include "Firestore/core/src/firebase/firestore/model/precondition.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
 
 namespace util = firebase::firestore::util;
 using firebase::firestore::auth::EmptyCredentialsProvider;
 using firebase::firestore::core::DatabaseInfo;
 using firebase::firestore::model::DatabaseId;
+using firebase::firestore::model::Precondition;
 using firebase::firestore::model::TargetId;
 
 NS_ASSUME_NONNULL_BEGIN
@@ -238,7 +240,7 @@ NS_ASSUME_NONNULL_BEGIN
        initWithKey:[FSTDocumentKey keyWithPathString:@"rooms/eros"]
              value:[[FSTObjectValue alloc]
                        initWithDictionary:@{@"name" : [FSTStringValue stringValue:@"Eros"]}]
-      precondition:[FSTPrecondition none]];
+      precondition:Precondition::None()];
 }
 
 @end
diff --git a/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm b/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
index d810aa6..362f46f 100644
--- a/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
+++ b/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
@@ -42,12 +42,14 @@
 
 #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/precondition.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
 #include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
 
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::model::DatabaseId;
 using firebase::firestore::model::FieldMask;
+using firebase::firestore::model::Precondition;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -78,13 +80,12 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testEncodesMutationBatch {
   FSTMutation *set = FSTTestSetMutation(@"foo/bar", @{ @"a" : @"b", @"num" : @1 });
-  FSTMutation *patch =
-      [[FSTPatchMutation alloc] initWithKey:FSTTestDocKey(@"bar/baz")
-                                  fieldMask:FieldMask{testutil::Field("a")}
-                                      value:FSTTestObjectValue(
-                                                @{ @"a" : @"b",
-                                                   @"num" : @1 })
-                               precondition:[FSTPrecondition preconditionWithExists:YES]];
+  FSTMutation *patch = [[FSTPatchMutation alloc] initWithKey:FSTTestDocKey(@"bar/baz")
+                                                   fieldMask:FieldMask{testutil::Field("a")}
+                                                       value:FSTTestObjectValue(
+                                                                 @{ @"a" : @"b",
+                                                                    @"num" : @1 })
+                                                precondition:Precondition::Exists(true)];
   FSTMutation *del = FSTTestDeleteMutation(@"baz/quux");
   FIRTimestamp *writeTime = [FIRTimestamp timestamp];
   FSTMutationBatch *model = [[FSTMutationBatch alloc] initWithBatchID:42
diff --git a/Firestore/Example/Tests/Model/FSTMutationTests.mm b/Firestore/Example/Tests/Model/FSTMutationTests.mm
index 9024b22..60cb7b8 100644
--- a/Firestore/Example/Tests/Model/FSTMutationTests.mm
+++ b/Firestore/Example/Tests/Model/FSTMutationTests.mm
@@ -26,11 +26,13 @@
 
 #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/precondition.h"
 #include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
 
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::model::DocumentKey;
 using firebase::firestore::model::FieldMask;
+using firebase::firestore::model::Precondition;
 
 @interface FSTMutationTests : XCTestCase
 @end
@@ -74,7 +76,7 @@ using firebase::firestore::model::FieldMask;
   FSTMutation *patch = [[FSTPatchMutation alloc] initWithKey:key
                                                    fieldMask:{testutil::Field("foo.bar")}
                                                        value:[FSTObjectValue objectValue]
-                                                precondition:[FSTPrecondition none]];
+                                                precondition:Precondition::None()];
   FSTMaybeDocument *patchedDoc =
       [patch applyTo:baseDoc baseDocument:baseDoc localWriteTime:_timestamp];
 
diff --git a/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm b/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
index c0e9cad..454b108 100644
--- a/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
+++ b/Firestore/Example/Tests/Remote/FSTSerializerBetaTests.mm
@@ -50,6 +50,7 @@
 #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/model/precondition.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
 #include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
 
@@ -58,6 +59,7 @@ namespace util = firebase::firestore::util;
 using firebase::firestore::model::DatabaseId;
 using firebase::firestore::model::FieldMask;
 using firebase::firestore::model::FieldTransform;
+using firebase::firestore::model::Precondition;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -377,12 +379,12 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 - (void)testEncodesSetMutationWithPrecondition {
-  FSTSetMutation *mutation = [[FSTSetMutation alloc]
-       initWithKey:FSTTestDocKey(@"foo/bar")
-             value:FSTTestObjectValue(
-                       @{ @"a" : @"b",
-                          @"num" : @1 })
-      precondition:[FSTPrecondition preconditionWithUpdateTime:FSTTestVersion(4)]];
+  FSTSetMutation *mutation =
+      [[FSTSetMutation alloc] initWithKey:FSTTestDocKey(@"foo/bar")
+                                    value:FSTTestObjectValue(
+                                              @{ @"a" : @"b",
+                                                 @"num" : @1 })
+                             precondition:Precondition::UpdateTime(testutil::Version(4))];
   GCFSWrite *proto = [GCFSWrite message];
   proto.update = [self.serializer encodedDocumentWithFields:mutation.value key:mutation.key];
   proto.currentDocument.updateTime =
diff --git a/Firestore/Example/Tests/Util/FSTHelpers.mm b/Firestore/Example/Tests/Util/FSTHelpers.mm
index 2e1082e..78b41a4 100644
--- a/Firestore/Example/Tests/Util/FSTHelpers.mm
+++ b/Firestore/Example/Tests/Util/FSTHelpers.mm
@@ -48,6 +48,7 @@
 #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/precondition.h"
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
 #include "Firestore/core/src/firebase/firestore/model/transform_operations.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
@@ -62,6 +63,7 @@ using firebase::firestore::model::FieldMask;
 using firebase::firestore::model::FieldPath;
 using firebase::firestore::model::FieldTransform;
 using firebase::firestore::model::FieldValue;
+using firebase::firestore::model::Precondition;
 using firebase::firestore::model::ResourcePath;
 using firebase::firestore::model::ServerTimestampTransform;
 using firebase::firestore::model::TransformOperation;
@@ -250,7 +252,7 @@ FSTDocumentSet *FSTTestDocSet(NSComparator comp, NSArray<FSTDocument *> *docs) {
 FSTSetMutation *FSTTestSetMutation(NSString *path, NSDictionary<NSString *, id> *values) {
   return [[FSTSetMutation alloc] initWithKey:FSTTestDocKey(path)
                                        value:FSTTestObjectValue(values)
-                                precondition:[FSTPrecondition none]];
+                                precondition:Precondition::None()];
 }
 
 FSTPatchMutation *FSTTestPatchMutation(const absl::string_view path,
@@ -274,7 +276,7 @@ FSTPatchMutation *FSTTestPatchMutation(const absl::string_view path,
   return [[FSTPatchMutation alloc] initWithKey:key
                                      fieldMask:mask
                                          value:objectValue
-                                  precondition:[FSTPrecondition preconditionWithExists:YES]];
+                                  precondition:Precondition::Exists(true)];
 }
 
 // For now this only creates TransformMutations with server timestamps.
@@ -291,8 +293,8 @@ FSTTransformMutation *FSTTestTransformMutation(NSString *path,
 }
 
 FSTDeleteMutation *FSTTestDeleteMutation(NSString *path) {
-  return [[FSTDeleteMutation alloc] initWithKey:FSTTestDocKey(path)
-                                   precondition:[FSTPrecondition none]];
+  return
+      [[FSTDeleteMutation alloc] initWithKey:FSTTestDocKey(path) precondition:Precondition::None()];
 }
 
 FSTMaybeDocumentDictionary *FSTTestDocUpdates(NSArray<FSTMaybeDocument *> *docs) {