fix(savedata): preserve existing saves on replace failure

core/libs/tests/SaveDataFileWriteFailure.cpp

@@ -0,0 +1,62 @@
+#include "prx/libSceSaveData/SaveDataFile.hpp"
+
+#include <chrono>
+#include <cstdio>
+#include <cstdlib>
+#include <filesystem>
+#include <fstream>
+#include <iterator>
+#include <string>
+#include <vector>
+
+static void Check(bool value, int line) {
+    if (!value) {
+        std::fprintf(stderr, "Save-data write failure check failed at line %d\n", line);
+        std::abort();
+    }
+}
+#define Require(value) Check((value), __LINE__)
+
+int main() {
+    const auto root = std::filesystem::temp_directory_path() /
+        ("anyps5-savedata-write-failure-" +
+         std::to_string(std::chrono::steady_clock::now().time_since_epoch().count()));
+    Require(std::filesystem::create_directory(root));
+
+    const auto savePath = root / "memory.dat";
+    const std::vector<char> oldData{'o', 'l', 'd'};
+    const std::vector<char> replacement{'n', 'e', 'w'};
+    {
+        std::ofstream file(savePath, std::ios::binary);
+        Require(file.is_open());
+        file.write(oldData.data(), static_cast<std::streamsize>(oldData.size()));
+        Require(static_cast<bool>(file));
+    }
+
+    int replaceAttempts = 0;
+    const bool replaced = savedata::replace_file_with(
+        savePath, replacement.data(), replacement.size(),
+        [&replaceAttempts, &savePath](const std::filesystem::path& temporary,
+                                      const std::filesystem::path& destination) {
+            ++replaceAttempts;
+            Require(destination == savePath);
+            auto expectedTemporary = savePath;
+            expectedTemporary += ".tmp";
+            Require(temporary == expectedTemporary);
+            return false;
+        });
+
+    Require(!replaced);
+    Require(replaceAttempts == 1);
+    std::vector<char> savedData;
+    {
+        std::ifstream savedFile(savePath, std::ios::binary);
+        savedData.assign(std::istreambuf_iterator<char>(savedFile), std::istreambuf_iterator<char>());
+    }
+    Require(savedData == oldData);
+    auto temporary = savePath;
+    temporary += ".tmp";
+    Require(!std::filesystem::exists(temporary));
+
+    std::filesystem::remove_all(root);
+}