Improve handling of read-only files

* Fix #3407
* Read-only files now disable auto-save and show as modified correctly. This allows the GUI to prompt to "save-as" instead of silently discarding changes when the read-only database is locked or closed.

src/core/Database.cpp

@@ -202,8 +202,12 @@ bool Database::save(QString* error, bool atomic, bool backup)
  */
 bool Database::save(const QString& filePath, QString* error, bool atomic, bool backup)
 {
-    Q_ASSERT(!m_data.isReadOnly);
-    if (m_data.isReadOnly) {
+    // Disallow saving to the same file if read-only
+    if (m_data.isReadOnly && filePath == m_data.filePath) {
+        Q_ASSERT(false);
+        if (error) {
+            *error = tr("Could not save, database file is read-only.");
+        }
         return false;
     }
 
@@ -741,10 +745,6 @@ bool Database::isModified() const
 
 void Database::markAsModified()
 {
-    if (isReadOnly()) {
-        return;
-    }
-
     m_modified = true;
     if (m_emitModified) {
         startModifiedTimer();
@@ -780,8 +780,6 @@ Database* Database::databaseByFilePath(const QString& filePath)
 
 void Database::startModifiedTimer()
 {
-    Q_ASSERT(!m_data.isReadOnly);
-
     if (!m_emitModified) {
         return;
     }

src/gui/DatabaseWidget.cpp

@@ -984,7 +984,10 @@ void DatabaseWidget::unlockDatabase(bool accepted)
     }
     replaceDatabase(db);
     if (db->isReadOnly()) {
-        showMessage(tr("File opened in read only mode."), MessageWidget::Warning, false, -1);
+        showMessage(tr("This database is opened in read only mode. Auto-save has been disabled."),
+                    MessageWidget::Warning,
+                    false,
+                    -1);
     }
 
     restoreGroupEntryFocus(m_groupBeforeLock, m_entryBeforeLock);
@@ -1225,7 +1228,7 @@ void DatabaseWidget::onGroupChanged(Group* group)
 
 void DatabaseWidget::onDatabaseModified()
 {
-    if (!m_blockAutoSave && config()->get("AutoSaveAfterEveryChange").toBool()) {
+    if (!m_blockAutoSave && config()->get("AutoSaveAfterEveryChange").toBool() && !m_db->isReadOnly()) {
         save();
     } else {
         // Only block once, then reset