From 0eb7012b5750939d8e44617dfcb3f2d3f0cbd8cd Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <tim.ledbetter@ladybird.org>
Date: Sat, 7 Feb 2026 21:30:27 +0000
Subject: [PATCH] AK: Add `TypedTransfer<T>::relocate()`

This moves objects from source to destination destructively, ensuring
the destructors are called if necessary.
---
 AK/TypedTransfer.h             | 18 +++++++
 Tests/AK/TestTypedTransfer.cpp | 89 ++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+)

diff --git a/AK/TypedTransfer.h b/AK/TypedTransfer.h
index 4b11b071928..a286913a81d 100644
--- a/AK/TypedTransfer.h
+++ b/AK/TypedTransfer.h
@@ -70,6 +70,24 @@ public:
         return true;
     }
 
+    static void relocate(T* destination, T* source, size_t count)
+    {
+        VERIFY(source + count <= destination || destination + count <= source);
+
+        if (count == 0)
+            return;
+
+        if constexpr (IsTriviallyRelocatable<T>) {
+            __builtin_memcpy(destination, source, count * sizeof(T));
+            return;
+        }
+
+        for (size_t i = 0; i < count; ++i) {
+            new (&destination[i]) T(AK::move(source[i]));
+            source[i].~T();
+        }
+    }
+
     static void delete_(T* ptr, size_t count)
     {
         if (count == 0)
diff --git a/Tests/AK/TestTypedTransfer.cpp b/Tests/AK/TestTypedTransfer.cpp
index 392d6a6600b..911701741f6 100644
--- a/Tests/AK/TestTypedTransfer.cpp
+++ b/Tests/AK/TestTypedTransfer.cpp
@@ -7,6 +7,7 @@
 #include <LibTest/TestCase.h>
 
 #include <AK/Array.h>
+#include <AK/ScopeGuard.h>
 #include <AK/TypedTransfer.h>
 
 struct NonPrimitiveIntWrapper {
@@ -18,6 +19,41 @@ struct NonPrimitiveIntWrapper {
     int m_value;
 };
 
+static_assert(IsTriviallyRelocatable<int>);
+
+struct NonTriviallyRelocatable {
+    NonTriviallyRelocatable(int value)
+        : m_value(value)
+    {
+        ++s_construct_count;
+    }
+
+    NonTriviallyRelocatable(NonTriviallyRelocatable&& other)
+        : m_value(other.m_value)
+    {
+        other.m_value = -1;
+        ++s_construct_count;
+    }
+
+    ~NonTriviallyRelocatable()
+    {
+        ++s_destruct_count;
+    }
+
+    NonTriviallyRelocatable(NonTriviallyRelocatable const&) = delete;
+    NonTriviallyRelocatable& operator=(NonTriviallyRelocatable const&) = delete;
+
+    int m_value;
+
+    static int s_construct_count;
+    static int s_destruct_count;
+};
+
+int NonTriviallyRelocatable::s_construct_count = 0;
+int NonTriviallyRelocatable::s_destruct_count = 0;
+
+static_assert(!IsTriviallyRelocatable<NonTriviallyRelocatable>);
+
 TEST_CASE(overlapping_source_and_destination_1)
 {
     Array<NonPrimitiveIntWrapper, 6> const expected { 3, 4, 5, 6, 5, 6 };
@@ -39,3 +75,56 @@ TEST_CASE(overlapping_source_and_destination_2)
     for (size_t i = 0; i < 6; ++i)
         EXPECT_EQ(actual[i].m_value, expected[i].m_value);
 }
+
+TEST_CASE(relocate_trivially_relocatable)
+{
+    Array<int, 4> source { 10, 20, 30, 40 };
+    alignas(int) u8 destination_storage[4 * sizeof(int)];
+    auto* destination = reinterpret_cast<int*>(destination_storage);
+
+    AK::TypedTransfer<int>::relocate(destination, source.data(), 4);
+
+    EXPECT_EQ(destination[0], 10);
+    EXPECT_EQ(destination[1], 20);
+    EXPECT_EQ(destination[2], 30);
+    EXPECT_EQ(destination[3], 40);
+}
+
+TEST_CASE(relocate_non_trivially_relocatable)
+{
+    alignas(NonTriviallyRelocatable) u8 source_storage[3 * sizeof(NonTriviallyRelocatable)];
+    alignas(NonTriviallyRelocatable) u8 destination_storage[3 * sizeof(NonTriviallyRelocatable)];
+    auto* source = reinterpret_cast<NonTriviallyRelocatable*>(source_storage);
+    auto* destination = reinterpret_cast<NonTriviallyRelocatable*>(destination_storage);
+
+    new (&source[0]) NonTriviallyRelocatable(100);
+    new (&source[1]) NonTriviallyRelocatable(200);
+    new (&source[2]) NonTriviallyRelocatable(300);
+
+    ScopeGuard cleanup([&] {
+        AK::TypedTransfer<NonTriviallyRelocatable>::delete_(destination, 3);
+    });
+
+    NonTriviallyRelocatable::s_construct_count = 0;
+    NonTriviallyRelocatable::s_destruct_count = 0;
+
+    AK::TypedTransfer<NonTriviallyRelocatable>::relocate(destination, source, 3);
+
+    EXPECT_EQ(destination[0].m_value, 100);
+    EXPECT_EQ(destination[1].m_value, 200);
+    EXPECT_EQ(destination[2].m_value, 300);
+
+    EXPECT_EQ(NonTriviallyRelocatable::s_construct_count, 3);
+    EXPECT_EQ(NonTriviallyRelocatable::s_destruct_count, 3);
+}
+
+TEST_CASE(relocate_zero_count)
+{
+    NonTriviallyRelocatable::s_construct_count = 0;
+    NonTriviallyRelocatable::s_destruct_count = 0;
+
+    AK::TypedTransfer<NonTriviallyRelocatable>::relocate(nullptr, nullptr, 0);
+
+    EXPECT_EQ(NonTriviallyRelocatable::s_construct_count, 0);
+    EXPECT_EQ(NonTriviallyRelocatable::s_destruct_count, 0);
+}