Fix availability of "Link with Qt" info bar

The info bar should never appear if the button is disabled,
for example because the Qt Creator directory is not accessible.

Fixes: QTCREATORBUG-23900
Change-Id: I819c87f5ca51f69f34bd462fca8e877be3544100
Reviewed-by: hjk <hjk@qt.io>

src/plugins/qtsupport/qtoptionspage.cpp

@@ -823,28 +823,41 @@ static QString linkingPurposeText()
         "Linking with a Qt installation automatically registers Qt versions and kits.");
 }
 
-void QtOptionsPageWidget::setupLinkWithQtButton()
+static bool canLinkWithQt(QString *toolTip)
 {
+    bool canLink = true;
     bool installSettingsExist;
     const Utils::optional<QString> installSettingsValue = currentlyLinkedQtDir(
         &installSettingsExist);
     QStringList tip;
     tip << linkingPurposeText();
     if (!FilePath::fromString(Core::ICore::resourcePath()).isWritablePath()) {
-        m_ui.linkWithQtButton->setEnabled(false);
+        canLink = false;
-        tip << tr("%1's resource directory is not writable.").arg(Core::Constants::IDE_DISPLAY_NAME);
+        tip << QtOptionsPageWidget::tr("%1's resource directory is not writable.")
+                   .arg(Core::Constants::IDE_DISPLAY_NAME);
     }
     // guard against redirecting Qt Creator that is part of a Qt installations
     // TODO this fails for pre-releases in the online installer
     // TODO this will fail when make Qt Creator non-required in the Qt installers
     if (installSettingsExist && !installSettingsValue) {
-        m_ui.linkWithQtButton->setEnabled(false);
+        canLink = false;
-        tip << tr("%1 is part of a Qt installation.").arg(Core::Constants::IDE_DISPLAY_NAME);
+        tip << QtOptionsPageWidget::tr("%1 is part of a Qt installation.")
+                   .arg(Core::Constants::IDE_DISPLAY_NAME);
     }
     const QString link = installSettingsValue ? *installSettingsValue : QString();
     if (!link.isEmpty())
-        tip << tr("%1 is currently linked to \"%2\".").arg(Core::Constants::IDE_DISPLAY_NAME, link);
+        tip << QtOptionsPageWidget::tr("%1 is currently linked to \"%2\".")
-    m_ui.linkWithQtButton->setToolTip(tip.join("\n\n"));
+                   .arg(Core::Constants::IDE_DISPLAY_NAME, link);
+    if (toolTip)
+        *toolTip = tip.join("\n\n");
+    return canLink;
+}
+
+void QtOptionsPageWidget::setupLinkWithQtButton()
+{
+    QString tip;
+    canLinkWithQt(&tip);
+    m_ui.linkWithQtButton->setToolTip(tip);
     connect(m_ui.linkWithQtButton, &QPushButton::clicked, this, &QtOptionsPage::linkWithQt);
 }
 
@@ -1018,6 +1031,16 @@ QtOptionsPage::QtOptionsPage()
     setWidgetCreator([] { return new QtOptionsPageWidget; });
 }
 
+bool QtOptionsPage::canLinkWithQt()
+{
+    return Internal::canLinkWithQt(nullptr);
+}
+
+bool QtOptionsPage::isLinkedWithQt()
+{
+    return currentlyLinkedQtDir(nullptr).has_value();
+}
+
 void QtOptionsPage::linkWithQt()
 {
     QtOptionsPageWidget::linkWithQt();

src/plugins/qtsupport/qtoptionspage.h

@@ -35,6 +35,8 @@ class QtOptionsPage final : public Core::IOptionsPage
 public:
     QtOptionsPage();
 
+    static bool canLinkWithQt();
+    static bool isLinkedWithQt();
     static void linkWithQt();
 };
 

src/plugins/qtsupport/qtsupportplugin.cpp

@@ -122,7 +122,7 @@ static void askAboutQtInstallation()
 {
     // if the install settings exist, the Qt Creator installation is (probably) already linked to
     // a Qt installation, so don't ask
-    if (QFile::exists(ICore::settings(QSettings::SystemScope)->fileName())
+    if (!QtOptionsPage::canLinkWithQt() || QtOptionsPage::isLinkedWithQt()
         || !ICore::infoBar()->canInfoBeAdded(kLinkWithQtInstallationSetting))
         return;