[Oracle] Skip low-memory prompt in background mode, guard with HAS_LZMA

Use QRegularExpression behind the same Qt version guard as
totalMemoryBytes() in availableMemoryBytes(), where a bare QRegExp
broke every Qt6 Linux build. hasAtLeastGiB() now treats a 0 reading
(unsupported platform or failed query) as unknown and skips the
low-memory prompt instead of misreading it as low memory.

libcockatrice_deck_list/libcockatrice/deck_list/deck_list.cpp

@@ -166,7 +166,7 @@ bool DeckList::readElement(QXmlStreamReader *xml)
     return true;
 }
 
-void writeMetadata(QXmlStreamWriter *xml, const DeckList::Metadata &metadata)
+static void writeMetadata(QXmlStreamWriter *xml, const DeckList::Metadata &metadata)
 {
     xml->writeTextElement("lastLoadedTimestamp", metadata.lastLoadedTimestamp);
     xml->writeTextElement("deckname", metadata.name);

libcockatrice_network/libcockatrice/network/server/remote/server_player_reference.h

@@ -24,7 +24,7 @@ public:
     {
         return playerId;
     }
-    bool operator==(const PlayerReference &other)
+    bool operator==(const PlayerReference &other) const
     {
         return ((roomId == other.roomId) && (gameId == other.gameId) && (playerId == other.playerId));
     }

libcockatrice_utility/libcockatrice/utility/system_memory_querier.cpp

@@ -84,7 +84,11 @@ qulonglong SystemMemoryQuerier::availableMemoryBytes()
     while (!in.atEnd()) {
         QString line = in.readLine();
         if (line.startsWith("MemAvailable:")) {
-            QStringList parts = line.split(QRegExp("\\s+"), Qt::SkipEmptyParts);
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+            QStringList parts = line.split(QRegExp("\\s+"), QString::SkipEmptyParts);
+#else
+            QStringList parts = line.split(QRegularExpression("\\s+"), Qt::SkipEmptyParts);
+#endif
             if (parts.size() >= 2)
                 return parts[1].toULongLong() * 1024;
         }

libcockatrice_utility/libcockatrice/utility/system_memory_querier.h

@@ -11,8 +11,14 @@ public:
 
     static bool hasAtLeastGiB(int gib)
     {
+        const qulonglong total = totalMemoryBytes();
+        // 0 means the amount could not be determined (unsupported platform or failed query).
+        // Treat it as unknown and skip the check instead of misreading it as low memory.
+        if (total == 0) {
+            return true;
+        }
         const qulonglong GiB = 1024ull * 1024ull * 1024ull;
-        return totalMemoryBytes() >= (qulonglong)gib * GiB;
+        return total >= (qulonglong)gib * GiB;
     }
 };
 

oracle/src/pages.cpp

@@ -188,21 +188,30 @@ void LoadSetsPage::initializePage()
     urlLineEdit->setText(wizard()->settings->value("allsetsurl", ALLSETS_URL).toString());
 
     // Memory check because Oracle parsing fails on systems with less than 4GiB for MTGJsons allPrintings.json
+    // The fallback URL is xz-compressed, so only offer it in builds that can read it.
+    // During background (automatic) updates there is no user to answer, so switch silently.
+#ifdef HAS_LZMA
     if (!SystemMemoryQuerier::hasAtLeastGiB(4) && urlLineEdit->text() == ALLSETS_URL) {
-        // Ask user whether to switch URL
+        if (wizard()->backgroundMode) {
-        QMessageBox msgBox(
-            QMessageBox::Question, tr("Low Memory Detected"),
-            tr("Your system has less than 4 GiB of memory.\n"
-               "Using the default AllPrintings URL may cause high memory usage and is known to fail as a result.\n\n"
-               "Would you like to switch to the direct-download pre-parsed URL instead? (Updated daily)"),
-            QMessageBox::Yes | QMessageBox::No, this);
-
-        msgBox.setDefaultButton(QMessageBox::Yes);
-
-        if (msgBox.exec() == QMessageBox::Yes) {
             urlLineEdit->setText(MTGXML_URL);
+        } else {
+            // Ask user whether to switch URL
+            QMessageBox msgBox(
+                QMessageBox::Question, tr("Low Memory Detected"),
+                tr("Your system has less than 4 GiB of memory.\n"
+                   "Using the default AllPrintings URL may cause high memory usage and is known to fail as a "
+                   "result.\n\n"
+                   "Would you like to switch to the direct-download pre-parsed URL instead? (Updated daily)"),
+                QMessageBox::Yes | QMessageBox::No, this);
+
+            msgBox.setDefaultButton(QMessageBox::Yes);
+
+            if (msgBox.exec() == QMessageBox::Yes) {
+                urlLineEdit->setText(MTGXML_URL);
+            }
         }
     }
+#endif
 
     progressLabel->hide();
     progressBar->hide();