AK+LibUnicode: Implement Unicode-aware UTF-16 case transformations

Author: https://github.com/trflynn89
Commit: a740bfd8ff
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5604
Reviewed-by: https://github.com/gmta ✅

Libraries/LibUnicode/CMakeLists.txt

@@ -17,6 +17,7 @@ set(SOURCES
     String.cpp
     TimeZone.cpp
     UnicodeKeywords.cpp
+    Utf16String.cpp
 )
 
 set(GENERATED_SOURCES ${CURRENT_LIB_GENERATED})

Libraries/LibUnicode/Utf16String.cpp

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Utf16String.h>
+#include <LibUnicode/ICU.h>
+
+#include <unicode/stringoptions.h>
+#include <unicode/translit.h>
+#include <unicode/unistr.h>
+
+// This file contains definitions of AK::Utf16String methods which require UCD data.
+
+namespace AK {
+
+Utf16String Utf16String::to_lowercase(Optional<StringView> const& locale) const
+{
+    if (has_ascii_storage() && !locale.has_value())
+        return to_ascii_lowercase();
+
+    Optional<Unicode::LocaleData&> locale_data;
+    if (locale.has_value())
+        locale_data = Unicode::LocaleData::for_locale(*locale);
+
+    auto icu_string = Unicode::icu_string(*this);
+    locale_data.has_value() ? icu_string.toLower(locale_data->locale()) : icu_string.toLower();
+
+    return Unicode::icu_string_to_utf16_string(icu_string);
+}
+
+Utf16String Utf16String::to_uppercase(Optional<StringView> const& locale) const
+{
+    if (has_ascii_storage() && !locale.has_value())
+        return to_ascii_uppercase();
+
+    Optional<Unicode::LocaleData&> locale_data;
+    if (locale.has_value())
+        locale_data = Unicode::LocaleData::for_locale(*locale);
+
+    auto icu_string = Unicode::icu_string(*this);
+    locale_data.has_value() ? icu_string.toUpper(locale_data->locale()) : icu_string.toUpper();
+
+    return Unicode::icu_string_to_utf16_string(icu_string);
+}
+
+Utf16String Utf16String::to_titlecase(Optional<StringView> const& locale, TrailingCodePointTransformation trailing_code_point_transformation) const
+{
+    Optional<Unicode::LocaleData&> locale_data;
+    if (locale.has_value())
+        locale_data = Unicode::LocaleData::for_locale(*locale);
+
+    u32 options = 0;
+    if (trailing_code_point_transformation == TrailingCodePointTransformation::PreserveExisting)
+        options |= U_TITLECASE_NO_LOWERCASE;
+
+    auto icu_string = Unicode::icu_string(*this);
+    locale_data.has_value()
+        ? icu_string.toTitle(nullptr, locale_data->locale(), options)
+        : icu_string.toTitle(nullptr, icu::Locale::getDefault(), options);
+
+    return Unicode::icu_string_to_utf16_string(icu_string);
+}
+
+Utf16String Utf16String::to_casefold() const
+{
+    auto icu_string = Unicode::icu_string(*this);
+    icu_string.foldCase();
+
+    return Unicode::icu_string_to_utf16_string(icu_string);
+}
+
+Utf16String Utf16String::to_fullwidth() const
+{
+    UErrorCode status = U_ZERO_ERROR;
+
+    auto const transliterator = adopt_own_if_nonnull(icu::Transliterator::createInstance("Halfwidth-Fullwidth", UTRANS_FORWARD, status));
+    VERIFY(Unicode::icu_success(status));
+
+    auto icu_string = Unicode::icu_string(*this);
+    transliterator->transliterate(icu_string);
+
+    return Unicode::icu_string_to_utf16_string(icu_string);
+}
+
+}