fix replacewith bug

Author: cherylEnkidu

Firestore/Swift/Tests/Integration/PipelineTests.swift

@@ -1266,7 +1266,7 @@ class PipelineIntegrationTests: FSTIntegrationTestCase {
 
     // Need to use nullable Sendable for comparison because 'others' is nested
     // and the areEqual function handles Sendable?
-    expectSnapshots(snapshot: snapshot, expected: [expectedBook1Transformed as [String: Sendable]])
+    expectSnapshots(snapshot: snapshot, expected: [expectedBook1Transformed])
   }
 
   // MARK: - Sample Stage Tests

Firestore/core/src/api/stages.cc

@@ -306,20 +306,37 @@ google_firestore_v1_Pipeline_Stage RemoveFieldsStage::to_proto() const {
   return result;
 }
 
+google_firestore_v1_Value ReplaceWith::ReplaceMode::to_proto() const {
+  google_firestore_v1_Value result;
+  result.which_value_type = google_firestore_v1_Value_string_value_tag;
+  switch (mode_) {
+    case FULL_REPLACE:
+      result.string_value = nanopb::MakeBytesArray("full_replace");
+      break;
+    case MERGE_PREFER_NEST:
+      result.string_value = nanopb::MakeBytesArray("merge_prefer_nest");
+      break;
+  }
+  return result;
+}
+
 google_firestore_v1_Pipeline_Stage ReplaceWith::to_proto() const {
   google_firestore_v1_Pipeline_Stage result;
   result.name = nanopb::MakeBytesArray("replace_with");
 
-  result.args_count = 1;
-  result.args = nanopb::MakeArray<google_firestore_v1_Value>(1);
+  result.args_count = 2;
+  result.args = nanopb::MakeArray<google_firestore_v1_Value>(2);
   result.args[0] = expr_->to_proto();
 
+  result.args[1] = mode_.to_proto();
+
   result.options_count = 0;
   result.options = nullptr;
   return result;
 }
 
-ReplaceWith::ReplaceWith(std::shared_ptr<Expr> expr) : expr_(std::move(expr)) {
+ReplaceWith::ReplaceWith(std::shared_ptr<Expr> expr, ReplaceMode mode)
+    : expr_(std::move(expr)), mode_(mode) {
 }
 
 Sample::Sample(std::string type, int64_t count, double percentage)

Firestore/core/src/api/stages.h

@@ -252,12 +252,31 @@ class RemoveFieldsStage : public Stage {
 
 class ReplaceWith : public Stage {
  public:
-  explicit ReplaceWith(std::shared_ptr<Expr> expr);
+  class ReplaceMode {
+   public:
+    enum Mode {
+      FULL_REPLACE,
+      MERGE_PREFER_NEST,
+      MERGE_PREFER_PARENT = FULL_REPLACE
+    };
+
+    explicit ReplaceMode(Mode mode) : mode_(mode) {
+    }
+    google_firestore_v1_Value to_proto() const;
+
+   private:
+    Mode mode_;
+  };
+
+  explicit ReplaceWith(
+      std::shared_ptr<Expr> expr,
+      ReplaceMode mode = ReplaceMode(ReplaceMode::Mode::FULL_REPLACE));
   ~ReplaceWith() override = default;
   google_firestore_v1_Pipeline_Stage to_proto() const override;
 
  private:
   std::shared_ptr<Expr> expr_;
+  ReplaceMode mode_;
 };
 
 class Sample : public Stage {