From 14e808e57456c0b9b36bd5bca2cf64216ed73eb1 Mon Sep 17 00:00:00 2001
From: Totto16 <tobiausgais@gmail.com>
Date: Thu, 14 Nov 2024 14:14:36 +0100
Subject: [PATCH] AK: Add Flatten Variant helper

This will be used in future commits.
It has to be present for types, that are generated by the IDL since the
IDL flattens variants of variants.
---
 AK/Variant.h             | 15 +++++++++++++++
 Tests/AK/TestVariant.cpp | 16 ++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/AK/Variant.h b/AK/Variant.h
index 7ae5619ef63..58a014da765 100644
--- a/AK/Variant.h
+++ b/AK/Variant.h
@@ -499,9 +499,24 @@ private:
 template<typename... Ts>
 struct TypeList<Variant<Ts...>> : TypeList<Ts...> { };
 
+namespace Detail {
+template<typename T1, typename T2>
+struct FlattenVariant;
+
+template<typename... Ts1, typename... Ts2>
+struct FlattenVariant<::AK::Variant<Ts1...>, ::AK::Variant<Ts2...>> {
+    using type = ::AK::Variant<Ts1..., Ts2...>;
+};
+
+}
+
+template<typename T1, typename T2>
+using FlattenVariant = Detail::FlattenVariant<T1, T2>::type;
+
 }
 
 #if USING_AK_GLOBALLY
 using AK::Empty;
+using AK::FlattenVariant;
 using AK::Variant;
 #endif
diff --git a/Tests/AK/TestVariant.cpp b/Tests/AK/TestVariant.cpp
index 44806a43101..63d61b7f6f3 100644
--- a/Tests/AK/TestVariant.cpp
+++ b/Tests/AK/TestVariant.cpp
@@ -302,3 +302,19 @@ TEST_CASE(variant_equality)
         EXPECT_EQ(variant1, variant2);
     }
 }
+
+TEST_CASE(flatten_variant)
+{
+    using InnerVariant = Variant<Empty, int>;
+    using OuterVariant = FlattenVariant<InnerVariant, Variant<float>>;
+    using MyVariant = Variant<Empty, int, float>;
+
+    EXPECT_EQ((TypeList<MyVariant>::size), 3u);
+    EXPECT_EQ((TypeList<OuterVariant>::size), 3u);
+    EXPECT((IsSame<OuterVariant, MyVariant>));
+
+    using OuterList = TypeList<OuterVariant>;
+    EXPECT((IsSame<typename OuterList::template Type<0>, Empty>));
+    EXPECT((IsSame<typename OuterList::template Type<1>, int>));
+    EXPECT((IsSame<typename OuterList::template Type<2>, float>));
+}