AK: Implement a flyweight string for Utf16String

Utf16FlyString more or less works exactly the same as FlyString. It will store the raw encoded data of the string instance. If the string is a short ASCII string, Utf16FlyString holds the ShortString bytes; else, Utf16FlyString holds a pointer to the Utf16StringData.
Author: https://github.com/trflynn89 Commit: 7f069efbc4 Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5388 Reviewed-by: https://github.com/shannonbooth ✅
2025-07-29 12:19:54 +00:00 · 2025-06-20 11:52:35 -04:00 · 2025-06-20 11:52:35 -04:00 · 7f069efbc4 · 2025-07-18 16:47:19 +00:00
commit 7f069efbc4
parent 2803d66d87
9 changed files with 423 additions and 4 deletions
--- a/Tests/AK/TestUtf16FlyString.cpp
+++ b/Tests/AK/TestUtf16FlyString.cpp
@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <AK/Utf16FlyString.h>
+
+TEST_CASE(empty_string)
+{
+    Utf16FlyString fly {};
+    EXPECT(fly.is_empty());
+    EXPECT_EQ(fly, ""sv);
+
+    // Short strings do not get stored in the fly string table.
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 0u);
+}
+
+TEST_CASE(short_string)
+{
+    Utf16FlyString fly1 { "foo"_utf16 };
+    EXPECT_EQ(fly1, "foo"sv);
+
+    Utf16FlyString fly2 { "foo"_utf16 };
+    EXPECT_EQ(fly2, "foo"sv);
+
+    Utf16FlyString fly3 { "bar"_utf16 };
+    EXPECT_EQ(fly3, "bar"sv);
+
+    EXPECT_EQ(fly1, fly2);
+    EXPECT_NE(fly1, fly3);
+    EXPECT_NE(fly2, fly3);
+
+    EXPECT(fly1.to_utf16_string().has_short_ascii_storage());
+    EXPECT(fly2.to_utf16_string().has_short_ascii_storage());
+    EXPECT(fly3.to_utf16_string().has_short_ascii_storage());
+
+    // Short strings do not get stored in the fly string table.
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 0u);
+}
+
+TEST_CASE(long_string)
+{
+    Utf16FlyString fly1 { "thisisdefinitelymorethan7bytes"_utf16 };
+    EXPECT_EQ(fly1, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    Utf16FlyString fly2 { "thisisdefinitelymorethan7bytes"_utf16 };
+    EXPECT_EQ(fly2, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    Utf16FlyString fly3 { "thisisalsoforsuremorethan7bytes"_utf16 };
+    EXPECT_EQ(fly3, "thisisalsoforsuremorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 2u);
+
+    EXPECT_EQ(fly1, fly2);
+    EXPECT_NE(fly1, fly3);
+    EXPECT_NE(fly2, fly3);
+
+    EXPECT(fly1.to_utf16_string().has_long_ascii_storage());
+    EXPECT(fly2.to_utf16_string().has_long_ascii_storage());
+    EXPECT(fly3.to_utf16_string().has_long_ascii_storage());
+}
+
+TEST_CASE(user_defined_literal)
+{
+    auto fly1 = "thisisdefinitelymorethan7bytes"_utf16_fly_string;
+    EXPECT_EQ(fly1, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    auto fly2 = "thisisdefinitelymorethan7bytes"_utf16_fly_string;
+    EXPECT_EQ(fly2, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    auto fly3 = u"thisisdefinitelymorethan7bytes"_utf16_fly_string;
+    EXPECT_EQ(fly3, u"thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    auto fly4 = "foo"_utf16_fly_string;
+    EXPECT_EQ(fly4, "foo"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    EXPECT_EQ(fly1, fly2);
+    EXPECT_EQ(fly1, fly3);
+    EXPECT_EQ(fly3, fly3);
+
+    EXPECT_NE(fly1, fly4);
+    EXPECT_NE(fly2, fly4);
+    EXPECT_NE(fly3, fly4);
+}
+
+TEST_CASE(fly_string_keep_string_data_alive)
+{
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 0u);
+    {
+        Utf16FlyString fly {};
+        {
+            auto string = "thisisdefinitelymorethan7bytes"_utf16;
+            fly = Utf16FlyString { string };
+            EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+        }
+
+        EXPECT_EQ(fly, "thisisdefinitelymorethan7bytes"sv);
+        EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+    }
+
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 0u);
+}
+
+TEST_CASE(moved_fly_string_becomes_empty)
+{
+    Utf16FlyString fly1 {};
+    EXPECT(fly1.is_empty());
+
+    Utf16FlyString fly2 { "thisisdefinitelymorethan7bytes"_utf16 };
+    EXPECT_EQ(fly2, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+
+    fly1 = move(fly2);
+
+    EXPECT(fly2.is_empty());
+    EXPECT_EQ(fly1, "thisisdefinitelymorethan7bytes"sv);
+    EXPECT_EQ(Utf16FlyString::number_of_utf16_fly_strings(), 1u);
+}
+
+TEST_CASE(is_one_of)
+{
+    auto foo = Utf16FlyString::from_utf8("foo"sv);
+    auto bar = Utf16FlyString::from_utf16(u"bar"sv);
+
+    EXPECT(foo.is_one_of(foo));
+    EXPECT(foo.is_one_of(foo, bar));
+    EXPECT(foo.is_one_of(bar, foo));
+    EXPECT(!foo.is_one_of(bar));
+
+    EXPECT(!bar.is_one_of("foo"sv));
+    EXPECT(bar.is_one_of("foo"sv, "bar"sv));
+    EXPECT(bar.is_one_of("bar"sv, "foo"sv));
+    EXPECT(bar.is_one_of("bar"sv));
+}