From a7e309d595353a8b045583ac07707f822ac744be Mon Sep 17 00:00:00 2001
From: FuzzTest Team <fuzztest@google.com>
Date: Tue, 26 May 2026 02:41:36 -0700
Subject: [PATCH] Refactor
 FlatbuffersTableUntypedDomainImpl::MutateSelectedField to use a visitor.

This change introduces MutateSelectedFieldVisitor to encapsulate the logic for mutating a specific field index. This allows for a more uniform handling of different field types, including recursive calls for nested tables, within the visitor pattern.

PiperOrigin-RevId: 921337267
---
 .../domains/flatbuffers_domain_impl.cc        | 21 ++--------
 .../domains/flatbuffers_domain_impl.h         | 38 +++++++++++++++----
 2 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/fuzztest/internal/domains/flatbuffers_domain_impl.cc b/fuzztest/internal/domains/flatbuffers_domain_impl.cc
index 90313441..75531b27 100644
--- a/fuzztest/internal/domains/flatbuffers_domain_impl.cc
+++ b/fuzztest/internal/domains/flatbuffers_domain_impl.cc
@@ -136,23 +136,10 @@ uint64_t FlatbuffersTableUntypedDomainImpl::MutateSelectedField(
     }
 
     ++field_counter;
-    if (field_counter == selected_field_index) {
-      VisitFlatbufferField(
-          schema_, field,
-          MutateVisitor{*this, prng, metadata, only_shrink, val});
-      return field_counter;
-    }
-
-    if (field->type()->base_type() == reflection::BaseType::Obj) {
-      auto sub_object = schema_->objects()->Get(field->type()->index());
-      if (!sub_object->is_struct()) {
-        field_counter +=
-            GetCachedDomain<FlatbuffersTableTag>(field).MutateSelectedField(
-                val[field->id()], prng, metadata, only_shrink,
-                selected_field_index - field_counter);
-      }
-      // TODO: Add support for structs.
-    }
+    VisitFlatbufferField(
+        schema_, field,
+        MutateSelectedFieldVisitor{*this, field_counter, val, prng, metadata,
+                                   only_shrink, selected_field_index});
 
     if (field_counter >= selected_field_index) {
       return field_counter;
diff --git a/fuzztest/internal/domains/flatbuffers_domain_impl.h b/fuzztest/internal/domains/flatbuffers_domain_impl.h
index 328b2e7b..54590714 100644
--- a/fuzztest/internal/domains/flatbuffers_domain_impl.h
+++ b/fuzztest/internal/domains/flatbuffers_domain_impl.h
@@ -618,22 +618,36 @@ class FlatbuffersTableUntypedDomainImpl
     }
   };
 
-  struct MutateVisitor {
+  struct MutateSelectedFieldVisitor {
     FlatbuffersTableUntypedDomainImpl& self;
+    uint64_t& field_counter;
+    corpus_type& val;
     absl::BitGenRef prng;
     const domain_implementor::MutationMetadata& metadata;
     bool only_shrink;
-    corpus_type& corpus_value;
+    uint64_t selected_field_index;
 
     template <typename T>
     void Visit(const reflection::Field* absl_nonnull field) {
-      auto& domain = self.GetCachedDomain<T>(field);
-      auto it = corpus_value.find(field->id());
-      if (it == corpus_value.end()) {
-        if (only_shrink) return;
-        it = corpus_value.try_emplace(field->id(), domain.Init(prng)).first;
+      if (!self.IsSupportedField(field)) return;
+      if (only_shrink && !val.contains(field->id())) return;
+
+      if (field_counter == selected_field_index) {
+        auto& domain = self.GetCachedDomain<T>(field);
+        auto it = val.find(field->id());
+        if (it == val.end()) {
+          if (only_shrink) return;
+          it = val.try_emplace(field->id(), domain.Init(prng)).first;
+        }
+        domain.Mutate(it->second, prng, metadata, only_shrink);
+      } else {
+        auto& domain = self.GetCachedDomain<T>(field);
+        if (auto it = val.find(field->id()); it != val.end()) {
+          field_counter += domain.MutateSelectedField(
+              it->second, prng, metadata, only_shrink,
+              selected_field_index - field_counter);
+        }
       }
-      domain.Mutate(it->second, prng, metadata, only_shrink);
     }
   };
 
@@ -764,6 +778,14 @@ class FlatbuffersTableDomainImpl
     return inner_->CountNumberOfFields(val.untyped_corpus);
   }
 
+  uint64_t MutateSelectedField(
+      corpus_type& val, absl::BitGenRef prng,
+      const domain_implementor::MutationMetadata& metadata, bool only_shrink,
+      uint64_t selected_field_index) {
+    return inner_->MutateSelectedField(val.untyped_corpus, prng, metadata,
+                                       only_shrink, selected_field_index);
+  }
+
   // Mutates the given corpus value.
   void Mutate(corpus_type& val, absl::BitGenRef prng,
               const domain_implementor::MutationMetadata& metadata,