Fix #1858284 [Automatic adding dialog has an unnecessary scrollbar](https://bugs.launchpad.net/calibre/+bug/1858284)

src/calibre/gui2/preferences/adding.ui

@@ -15,7 +15,7 @@
   </property>
   <layout class="QGridLayout" name="gridLayout">
    <item row="0" column="0">
-    <widget class="QTabWidget" name="tabWidget">
+    <widget class="ScrollingTabWidget" name="tabWidget">
      <property name="currentIndex">
       <number>2</number>
      </property>
@@ -445,6 +445,12 @@ that have been explicitly ignored below.</string>
    <extends>QLineEdit</extends>
    <header>calibre/gui2/widgets.h</header>
   </customwidget>
+  <customwidget>
+   <class>ScrollingTabWidget</class>
+   <extends>QTabWidget</extends>
+   <header>calibre/gui2/widgets2.h</header>
+   <container>1</container>
+  </customwidget>
  </customwidgets>
  <resources>
   <include location="../../../../resources/images.qrc"/>

src/calibre/gui2/preferences/look_feel.ui

@@ -15,7 +15,7 @@
   </property>
   <layout class="QGridLayout" name="gridLayout_2">
    <item row="0" column="0">
-    <widget class="QTabWidget" name="tabWidget">
+    <widget class="ScrollingTabWidget" name="tabWidget">
      <property name="currentIndex">
       <number>2</number>
      </property>
@@ -1319,6 +1319,12 @@ column being examined (the left-hand pane)</string>
    <extends>QComboBox</extends>
    <header>calibre/gui2/complete2.h</header>
   </customwidget>
+  <customwidget>
+   <class>ScrollingTabWidget</class>
+   <extends>QTabWidget</extends>
+   <header>calibre/gui2/widgets2.h</header>
+   <container>1</container>
+  </customwidget>
  </customwidgets>
  <resources>
   <include location="../../../../resources/images.qrc"/>

src/calibre/gui2/widgets2.py

@@ -8,17 +8,17 @@ import weakref
 
 from PyQt5.Qt import (
     QAbstractListModel, QApplication, QCheckBox, QColor, QColorDialog, QComboBox,
-    QDialog, QDialogButtonBox, QFont, QIcon, QKeySequence, QLabel, QLayout,
-    QModelIndex, QPalette, QPixmap, QPoint, QPushButton, QRect, QSize, QSizePolicy,
-    QStyle, QStyledItemDelegate, Qt, QTextBrowser, QToolButton, QUndoCommand, QFontInfo,
-    QUndoStack, QWidget, pyqtSignal
+    QDialog, QDialogButtonBox, QFont, QFontInfo, QIcon, QKeySequence, QLabel,
+    QLayout, QModelIndex, QPalette, QPixmap, QPoint, QPushButton, QRect, QScrollArea,
+    QSize, QSizePolicy, QStyle, QStyledItemDelegate, Qt, QTabWidget, QTextBrowser,
+    QToolButton, QUndoCommand, QUndoStack, QWidget, pyqtSignal
 )
 
 from calibre.ebooks.metadata import rating_to_stars
-from calibre.utils.config_base import tweaks
 from calibre.gui2 import gprefs, rating_font
 from calibre.gui2.complete2 import EditWithComplete, LineEdit
 from calibre.gui2.widgets import history
+from calibre.utils.config_base import tweaks
 from polyglot.builtins import unicode_type
 
 
@@ -482,6 +482,30 @@ class HTMLDisplay(QTextBrowser):
         self.anchor_clicked.emit(qurl)
 
 
+class ScrollingTabWidget(QTabWidget):
+
+    def __init__(self, parent=None):
+        QTabWidget.__init__(self, parent)
+
+    def wrap_widget(self, page):
+        sw = QScrollArea(self)
+        sw.setWidget(page)
+        sw.setWidgetResizable(True)
+        page.setAutoFillBackground(False)
+        sw.setStyleSheet('QScrollArea { background: transparent }')
+        return sw
+
+    def indexOf(self, page):
+        for i in range(self.count()):
+            t = self.widget(i)
+            if t.widget() is page:
+                return i
+        return -1
+
+    def addTab(self, page, *args):
+        return QTabWidget.addTab(self, self.wrap_widget(page), *args)
+
+
 if __name__ == '__main__':
     from calibre.gui2 import Application
     app = Application([])