Fix problem of saving pdf switches from thumbnail view in sidebar to contents view

Summary:
When save/save as functions are called they internally call the openFile() function, in the open file function the side bar item is set to Table of Contents (ToC) item

```
if ( m_document->metaData( QStringLiteral("OpenTOC") ).toBool() && m_sidebar->isItemEnabled( m_toc ) && !m_sidebar->isCollapsed() && m_sidebar->currentItem() != m_toc )
{
     m_sidebar->setCurrentItem( m_toc, Sidebar::DoNotUncollapseIfCollapsed );
}
```
so I just store the sidebar's item before saving and then set this item back if changed.

BUG: 389668

Reviewers: #okular

Subscribers: aacid, okular-devel

Tags: #okular

Differential Revision: https://phabricator.kde.org/D14740

autotests/parttest.cpp

@@ -17,6 +17,7 @@
 #include "../core/page.h"
 #include "../part.h"
 #include "../ui/toc.h"
+#include "../ui/sidebar.h"
 #include "../ui/pageview.h"
 
 #include "../generators/poppler/config-okular-poppler.h"
@@ -95,6 +96,7 @@ class PartTest
         void test388288();
         void testSaveAs();
         void testSaveAs_data();
+        void testSidebarItemAfterSaving();
         void testSaveAsUndoStackAnnotations();
         void testSaveAsUndoStackAnnotations_data();
         void testSaveAsUndoStackForms();
@@ -939,6 +941,23 @@ void PartTest::testSaveAs_data()
     QTest::newRow("jpg") << KDESRCDIR "data/potato.jpg" << "jpg" << false << true;
 }
 
+void PartTest::testSidebarItemAfterSaving()
+{
+    QVariantList dummyArgs;
+    Okular::Part part(nullptr, nullptr, dummyArgs);
+    QWidget *currentSidebarItem = part.m_sidebar->currentItem(); // thumbnails
+    openDocument(&part, QStringLiteral(KDESRCDIR "data/tocreload.pdf"));
+    // since it has TOC it changes to TOC
+    QVERIFY(currentSidebarItem != part.m_sidebar->currentItem());
+    // now change back to thumbnails
+    part.m_sidebar->setCurrentItem(currentSidebarItem);
+
+    part.saveAs(QUrl::fromLocalFile(QStringLiteral(KDESRCDIR "data/tocreload.pdf")));
+
+    // Check it is still thumbnails after saving
+    QCOMPARE(currentSidebarItem, part.m_sidebar->currentItem());
+}
+
 void PartTest::testSaveAsUndoStackAnnotations()
 {
     QFETCH(QString, file);

part.cpp

@@ -2730,6 +2730,7 @@ bool Part::saveAs( const QUrl & saveUrl, SaveAsFlags flags )
     // Make the generator use the new new file instead of the old one
     if ( m_document->canSwapBackingFile() && !m_documentOpenWithPassword )
     {
+        QWidget *currentSidebarItem = m_sidebar->currentItem();
         // this calls openFile internally, which in turn actually calls
         // m_document->swapBackingFile() instead of the regular loadDocument
         if ( openUrl( saveUrl, true /* swapInsteadOfOpening */ ) )
@@ -2743,6 +2744,9 @@ bool Part::saveAs( const QUrl & saveUrl, SaveAsFlags flags )
         {
             reloadedCorrectly = false;
         }
+
+        if ( m_sidebar->currentItem() != currentSidebarItem )
+            m_sidebar->setCurrentItem( currentSidebarItem );
     }
     else
     {

ui/sidebar.h

@@ -11,11 +11,12 @@
 #define _SIDEBAR_H_
 
 #include <qwidget.h>
+#include "okularpart_export.h"
 
 class QIcon;
 class QListWidgetItem;
 
-class Sidebar : public QWidget
+class OKULARPART_EXPORT Sidebar : public QWidget
 {
     Q_OBJECT
     public: