Core: Warn the user if the settings file cannot be read

Do an initial check and if it fails, warn the user that they cannot
expect subsequent operations to succeed.

Task-number: QTCREATORBUG-18294
Change-Id: I3bb323cf7b7ed99f97258da94cfd7669f8520717
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/coreplugin/coreplugin.cpp

@@ -27,6 +27,7 @@
 #include "designmode.h"
 #include "editmode.h"
 #include "helpmanager.h"
+#include "icore.h"
 #include "idocument.h"
 #include "infobar.h"
 #include "iwizardfactory.h"
@@ -63,6 +64,8 @@
 #include <QDebug>
 #include <QDir>
 #include <QMenu>
+#include <QMessageBox>
+#include <QSettings>
 #include <QUuid>
 
 #include <cstdlib>
@@ -232,6 +235,7 @@ void CorePlugin::extensionsInitialized()
         errorOverview->setModal(true);
         errorOverview->show();
     }
+    checkSettings();
 }
 
 bool CorePlugin::delayedInitialize()
@@ -295,6 +299,45 @@ void CorePlugin::addToPathChooserContextMenu(Utils::PathChooser *pathChooser, QM
         menu->insertSeparator(firstAction);
 }
 
+void CorePlugin::checkSettings()
+{
+    const auto showMsgBox = [this](const QString &msg, QMessageBox::Icon icon) {
+        connect(ICore::instance(), &ICore::coreOpened, this, [msg, icon]() {
+            QMessageBox msgBox(ICore::dialogParent());
+            msgBox.setWindowTitle(tr("Settings File Error"));
+            msgBox.setText(msg);
+            msgBox.setIcon(icon);
+            msgBox.exec();
+        }, Qt::QueuedConnection);
+    };
+    const QSettings * const userSettings = ICore::settings();
+    QString errorDetails;
+    switch (userSettings->status()) {
+    case QSettings::NoError: {
+        const QFileInfo fi(userSettings->fileName());
+        if (fi.exists() && !fi.isWritable()) {
+            const QString errorMsg = tr("The settings file \"%1\" is not writable.\n"
+                    "You will not be able to store any %2 settings.")
+                    .arg(QDir::toNativeSeparators(userSettings->fileName()),
+                         QLatin1String(Core::Constants::IDE_DISPLAY_NAME));
+            showMsgBox(errorMsg, QMessageBox::Warning);
+        }
+        return;
+    }
+    case QSettings::AccessError:
+        errorDetails = tr("The file is not readable.");
+        break;
+    case QSettings::FormatError:
+        errorDetails = tr("The file is invalid.");
+        break;
+    }
+    const QString errorMsg = tr("Error reading settings file \"%1\": %2\n"
+            "You will likely experience further problems using this instance of %3.")
+            .arg(QDir::toNativeSeparators(userSettings->fileName()), errorDetails,
+                 QLatin1String(Core::Constants::IDE_DISPLAY_NAME));
+    showMsgBox(errorMsg, QMessageBox::Critical);
+}
+
 ExtensionSystem::IPlugin::ShutdownFlag CorePlugin::aboutToShutdown()
 {
     Find::aboutToShutdown();

src/plugins/coreplugin/coreplugin.h

@@ -80,6 +80,7 @@ private slots:
 
 private:
     static void addToPathChooserContextMenu(Utils::PathChooser *pathChooser, QMenu *menu);
+    void checkSettings();
 
     MainWindow *m_mainWindow = nullptr;
     EditMode *m_editMode = nullptr;