Warn user on launch if there is not enough available RAM (#5249)

launcher/CMakeLists.txt

@@ -260,6 +260,8 @@ set(MINECRAFT_SOURCES
     minecraft/launch/ClaimAccount.h
     minecraft/launch/CreateGameFolders.cpp
     minecraft/launch/CreateGameFolders.h
+    minecraft/launch/EnsureAvailableMemory.cpp
+    minecraft/launch/EnsureAvailableMemory.h
     minecraft/launch/EnsureOfflineLibraries.cpp
     minecraft/launch/EnsureOfflineLibraries.h
     minecraft/launch/ModMinecraftJar.cpp

launcher/minecraft/MinecraftInstance.cpp

@@ -59,6 +59,7 @@
 #include "minecraft/launch/AutoInstallJava.h"
 #include "minecraft/launch/ClaimAccount.h"
 #include "minecraft/launch/CreateGameFolders.h"
+#include "minecraft/launch/EnsureAvailableMemory.h"
 #include "minecraft/launch/EnsureOfflineLibraries.h"
 #include "minecraft/launch/ExtractNatives.h"
 #include "minecraft/launch/LauncherPartLaunch.h"
@@ -1191,6 +1192,11 @@ LaunchTask* MinecraftInstance::createLaunchTask(AuthSessionPtr session, Minecraf
         process->appendStep(makeShared<ScanModFolders>(pptr));
     }
 
+    // make sure we have enough RAM, warn the user if we don't
+    {
+        process->appendStep(makeShared<EnsureAvailableMemory>(pptr, this));
+    }
+
     // print some instance info here...
     {
         process->appendStep(makeShared<PrintInstanceInfo>(pptr, session, targetToJoin));

launcher/minecraft/launch/EnsureAvailableMemory.cpp

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher - Minecraft Launcher
+ *  Copyright (C) 2026 Octol1ttle <l1ttleofficial@outlook.com>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "EnsureAvailableMemory.h"
+
+#include "HardwareInfo.h"
+#include "ui/dialogs/CustomMessageBox.h"
+
+EnsureAvailableMemory::EnsureAvailableMemory(LaunchTask* parent, MinecraftInstance* instance) : LaunchStep(parent), m_instance(instance) {}
+
+void EnsureAvailableMemory::executeTask()
+{
+    const uint64_t available = HardwareInfo::availableRamMiB();
+    const uint64_t min = m_instance->settings()->get("MinMemAlloc").toUInt();
+    const uint64_t max = m_instance->settings()->get("MaxMemAlloc").toUInt();
+    const uint64_t required = std::max(min, max);
+
+    if (required > available) {
+        auto* dialog = CustomMessageBox::selectable(
+            nullptr, tr("Not enough RAM"),
+            tr("There is not enough RAM available to launch this instance with the current memory settings.\n\n"
+               "Required: %1 MiB\nAvailable: %2 MiB\n\n"
+               "Continue anyway? This may cause slowdowns in the game and your system.")
+                .arg(required)
+                .arg(available),
+            QMessageBox::Icon::Warning, QMessageBox::StandardButton::Yes | QMessageBox::StandardButton::No,
+            QMessageBox::StandardButton::No);
+        const auto response = dialog->exec();
+        dialog->deleteLater();
+
+        const auto message = tr("Not enough RAM available to launch this instance");
+        if (response == QMessageBox::No) {
+            emit logLine(message, MessageLevel::Fatal);
+            emitFailed(message);
+            return;
+        }
+
+        emit logLine(message, MessageLevel::Warning);
+    }
+
+    emitSucceeded();
+}

launcher/minecraft/launch/EnsureAvailableMemory.h

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-3.0-only
+/*
+ *  Prism Launcher - Minecraft Launcher
+ *  Copyright (C) 2026 Octol1ttle <l1ttleofficial@outlook.com>
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, version 3.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "launch/LaunchStep.h"
+#include "minecraft/MinecraftInstance.h"
+
+class EnsureAvailableMemory : public LaunchStep {
+    Q_OBJECT
+
+   public:
+    explicit EnsureAvailableMemory(LaunchTask* parent, MinecraftInstance* instance);
+    ~EnsureAvailableMemory() override = default;
+
+    void executeTask() override;
+    bool canAbort() const override { return false; }
+
+   private:
+    MinecraftInstance* m_instance;
+};