native: Drop C++17 deprecated codecvt and use JNI instead, add modern ICU lib for future android API 31

app/src/main/cpp/CMakeLists.txt

@@ -68,4 +68,8 @@ target_link_libraries(${CMAKE_PROJECT_NAME}
     log
     fmt)
 
+if (ANDROID AND ANDROID_PLATFORM_LEVEL GREATER_EQUAL 31)
+    target_link_libraries(${CMAKE_PROJECT_NAME} icu)
+endif()
+
 target_compile_features(${CMAKE_PROJECT_NAME} PRIVATE cxx_std_23)

app/src/main/cpp/GakumasLocalify/Misc.cpp

@@ -1,11 +1,12 @@
 #include "Misc.hpp"
 
-#include <codecvt>
-#include <locale>
 #include "fmt/core.h"
 
 #ifndef GKMS_WINDOWS
     #include <jni.h>
+    #if defined(__ANDROID__) && __ANDROID_API__ >= 31
+        #include <unicode/ustring.h>
+    #endif
     
     extern JavaVM* g_javaVM;
 #else
@@ -32,14 +33,136 @@ namespace GakumasLocal::Misc {
         return utility::conversions::utf16_to_utf8(wstr);
     }
 #else
+    namespace {
+        jclass GetStringClass(JNIEnv* env) {
+            static jclass stringClass = nullptr;
+            if (stringClass) return stringClass;
+
+            jclass localClass = env->FindClass("java/lang/String");
+            if (!localClass) return nullptr;
+            stringClass = reinterpret_cast<jclass>(env->NewGlobalRef(localClass));
+            env->DeleteLocalRef(localClass);
+            return stringClass;
+        }
+
+        jstring GetUtf8CharsetName(JNIEnv* env) {
+            static jstring utf8Charset = nullptr;
+            if (utf8Charset) return utf8Charset;
+
+            jstring localUtf8 = env->NewStringUTF("UTF-8");
+            if (!localUtf8) return nullptr;
+            utf8Charset = reinterpret_cast<jstring>(env->NewGlobalRef(localUtf8));
+            env->DeleteLocalRef(localUtf8);
+            return utf8Charset;
+        }
+    }
+
     std::u16string ToUTF16(const std::string_view& str) {
-        std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> utf16conv;
+#if defined(__ANDROID__) && __ANDROID_API__ >= 31
-        return utf16conv.from_bytes(str.data(), str.data() + str.size());
+        UErrorCode status = U_ZERO_ERROR;
+        int32_t outLen = 0;
+        u_strFromUTF8(nullptr, 0, &outLen, str.data(), static_cast<int32_t>(str.size()), &status);
+        if (status != U_BUFFER_OVERFLOW_ERROR && U_FAILURE(status)) return {};
+
+        status = U_ZERO_ERROR;
+        std::u16string out(outLen, u'\0');
+        u_strFromUTF8(
+                reinterpret_cast<UChar*>(out.data()),
+                outLen,
+                &outLen,
+                str.data(),
+                static_cast<int32_t>(str.size()),
+                &status);
+        if (U_FAILURE(status)) return {};
+        out.resize(outLen);
+        return out;
+#else
+        JNIEnv* env = GetJNIEnv();
+        if (!env) return {};
+
+        jclass stringClass = GetStringClass(env);
+        jstring utf8Charset = GetUtf8CharsetName(env);
+        if (!stringClass || !utf8Charset) return {};
+
+        jmethodID ctor = env->GetMethodID(stringClass, "<init>", "([BLjava/lang/String;)V");
+        if (!ctor) return {};
+
+        jbyteArray bytes = env->NewByteArray(static_cast<jsize>(str.size()));
+        if (!bytes) return {};
+        env->SetByteArrayRegion(bytes, 0, static_cast<jsize>(str.size()), reinterpret_cast<const jbyte*>(str.data()));
+
+        jstring jstr = reinterpret_cast<jstring>(env->NewObject(stringClass, ctor, bytes, utf8Charset));
+        env->DeleteLocalRef(bytes);
+        if (!jstr || env->ExceptionCheck()) {
+            env->ExceptionClear();
+            if (jstr) env->DeleteLocalRef(jstr);
+            return {};
+        }
+
+        const jsize len = env->GetStringLength(jstr);
+        const jchar* chars = env->GetStringChars(jstr, nullptr);
+        if (!chars) {
+            env->DeleteLocalRef(jstr);
+            return {};
+        }
+
+        std::u16string out(reinterpret_cast<const char16_t*>(chars), reinterpret_cast<const char16_t*>(chars) + len);
+        env->ReleaseStringChars(jstr, chars);
+        env->DeleteLocalRef(jstr);
+        return out;
+#endif
     }
 
     std::string ToUTF8(const std::u16string_view& str) {
-        std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> utf16conv;
+#if defined(__ANDROID__) && __ANDROID_API__ >= 31
-        return utf16conv.to_bytes(str.data(), str.data() + str.size());
+        UErrorCode status = U_ZERO_ERROR;
+        int32_t outLen = 0;
+        u_strToUTF8(nullptr, 0, &outLen, reinterpret_cast<const UChar*>(str.data()), static_cast<int32_t>(str.size()), &status);
+        if (status != U_BUFFER_OVERFLOW_ERROR && U_FAILURE(status)) return {};
+
+        status = U_ZERO_ERROR;
+        std::string out(outLen, '\0');
+        u_strToUTF8(
+                out.data(),
+                outLen,
+                &outLen,
+                reinterpret_cast<const UChar*>(str.data()),
+                static_cast<int32_t>(str.size()),
+                &status);
+        if (U_FAILURE(status)) return {};
+        out.resize(outLen);
+        return out;
+#else
+        JNIEnv* env = GetJNIEnv();
+        if (!env) return {};
+
+        jclass stringClass = GetStringClass(env);
+        jstring utf8Charset = GetUtf8CharsetName(env);
+        if (!stringClass || !utf8Charset) return {};
+
+        jstring jstr = env->NewString(reinterpret_cast<const jchar*>(str.data()), static_cast<jsize>(str.size()));
+        if (!jstr) return {};
+
+        jmethodID getBytes = env->GetMethodID(stringClass, "getBytes", "(Ljava/lang/String;)[B");
+        if (!getBytes) {
+            env->DeleteLocalRef(jstr);
+            return {};
+        }
+
+        jbyteArray bytes = reinterpret_cast<jbyteArray>(env->CallObjectMethod(jstr, getBytes, utf8Charset));
+        env->DeleteLocalRef(jstr);
+        if (!bytes || env->ExceptionCheck()) {
+            env->ExceptionClear();
+            if (bytes) env->DeleteLocalRef(bytes);
+            return {};
+        }
+
+        const jsize len = env->GetArrayLength(bytes);
+        std::string out(static_cast<size_t>(len), '\0');
+        env->GetByteArrayRegion(bytes, 0, len, reinterpret_cast<jbyte*>(out.data()));
+        env->DeleteLocalRef(bytes);
+        return out;
+#endif
     }
 #endif