Display instructions when no search plugin is installed.

src/gui/search/searchwidget.cpp

@@ -118,6 +118,8 @@ SearchWidget::SearchWidget(MainWindow *mainWindow)
     fillCatCombobox();
     fillPluginComboBox();
 
+    selectActivePage();
+
     connect(m_ui->m_searchPattern, SIGNAL(returnPressed()), m_ui->searchButton, SLOT(click()));
     connect(m_ui->m_searchPattern, SIGNAL(textEdited(QString)), this, SLOT(searchTextEdited(QString)));
     connect(m_ui->selectPlugin, SIGNAL(currentIndexChanged(int)), this, SLOT(selectMultipleBox(int)));
@@ -169,6 +171,24 @@ QString SearchWidget::selectedPlugin() const
     return m_ui->selectPlugin->itemData(m_ui->selectPlugin->currentIndex()).toString();
 }
 
+void SearchWidget::selectActivePage()
+{
+    if (m_searchEngine->allPlugins().isEmpty()) {
+        m_ui->stackedPages->setCurrentWidget(m_ui->emptyPage);
+        m_ui->m_searchPattern->setEnabled(false);
+        m_ui->comboCategory->setEnabled(false);
+        m_ui->selectPlugin->setEnabled(false);
+        m_ui->searchButton->setEnabled(false);
+    }
+    else {
+        m_ui->stackedPages->setCurrentWidget(m_ui->searchPage);
+        m_ui->m_searchPattern->setEnabled(true);
+        m_ui->comboCategory->setEnabled(true);
+        m_ui->selectPlugin->setEnabled(true);
+        m_ui->searchButton->setEnabled(true);
+    }
+}
+
 SearchWidget::~SearchWidget()
 {
     qDebug("Search destruction");
@@ -224,6 +244,7 @@ void SearchWidget::on_pluginsButton_clicked()
     PluginSelectDlg *dlg = new PluginSelectDlg(m_searchEngine, this);
     connect(dlg, SIGNAL(pluginsChanged()), this, SLOT(fillCatCombobox()));
     connect(dlg, SIGNAL(pluginsChanged()), this, SLOT(fillPluginComboBox()));
+    connect(dlg, &PluginSelectDlg::pluginsChanged, this, &SearchWidget::selectActivePage);
 }
 
 void SearchWidget::searchTextEdited(QString)

src/gui/search/searchwidget.h

@@ -82,6 +82,7 @@ private slots:
 
     void fillCatCombobox();
     void fillPluginComboBox();
+    void selectActivePage();
     void searchTextEdited(QString);
 
 private:

src/gui/search/searchwidget.ui

@@ -13,7 +13,7 @@
   <property name="windowTitle">
    <string>Search</string>
   </property>
-  <layout class="QVBoxLayout" name="verticalLayout_2">
+  <layout class="QVBoxLayout" name="verticalLayout_3">
    <item>
     <layout class="QHBoxLayout" name="searchBarLayout">
      <item>
@@ -54,6 +54,52 @@
      </item>
     </layout>
    </item>
+   <item>
+    <widget class="QStackedWidget" name="stackedPages">
+     <property name="currentIndex">
+      <number>1</number>
+     </property>
+     <widget class="QWidget" name="emptyPage">
+      <layout class="QVBoxLayout" name="verticalLayout">
+       <property name="leftMargin">
+        <number>0</number>
+       </property>
+       <property name="topMargin">
+        <number>0</number>
+       </property>
+       <property name="rightMargin">
+        <number>0</number>
+       </property>
+       <property name="bottomMargin">
+        <number>0</number>
+       </property>
+       <item>
+        <widget class="QLabel" name="label">
+         <property name="text">
+          <string>There aren't any search plugins installed.
+Click the &quot;Search plugins...&quot; button at the bottom right of the window to install some.</string>
+         </property>
+         <property name="alignment">
+          <set>Qt::AlignCenter</set>
+         </property>
+        </widget>
+       </item>
+      </layout>
+     </widget>
+     <widget class="QWidget" name="searchPage">
+      <layout class="QVBoxLayout" name="verticalLayout_2">
+       <property name="leftMargin">
+        <number>0</number>
+       </property>
+       <property name="topMargin">
+        <number>0</number>
+       </property>
+       <property name="rightMargin">
+        <number>0</number>
+       </property>
+       <property name="bottomMargin">
+        <number>0</number>
+       </property>
        <item>
         <widget class="QTabWidget" name="tabWidget">
          <property name="tabsClosable">
@@ -61,6 +107,10 @@
          </property>
         </widget>
        </item>
+      </layout>
+     </widget>
+    </widget>
+   </item>
    <item>
     <layout class="QHBoxLayout" name="layout2">
      <item>