Help: Fix issues with scrolling to right position

The different viewer backends have different issues with scrolling to
the right position if the URL contains an anchor. In all combinations of
"viewer was visible/invisible when help was requested" and "viewer last
showed the same/a different page then the requested URL".

Move the special logic from help plugin to the viewer backends.

Task-number: QTCREATORBUG-15548
Change-Id: I962c90695ceaee48800a3590676e1d28343cf790
Reviewed-by: Karsten Heimrich <karsten.heimrich@theqtcompany.com>
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/help/helpplugin.cpp

@@ -593,14 +593,9 @@ void HelpPlugin::showContextHelp()
             .arg(contextHelpId)
             .arg(creatorTheme()->color(Theme::TextColorNormal).name()));
     } else {
-        const QUrl &oldSource = viewer->source();
-        if (source != oldSource) {
-            viewer->stop();
-            viewer->setSource(source); // triggers loadFinished which triggers id highlighting
-        } else {
-            viewer->scrollToAnchor(source.fragment());
-        }
         viewer->setFocus();
+        viewer->stop();
+        viewer->setSource(source); // triggers loadFinished which triggers id highlighting
         ICore::raiseWindow(viewer);
     }
 }

src/plugins/help/helpviewer.h

@@ -57,7 +57,6 @@ public:
     virtual QUrl source() const = 0;
     // metacall in HelpPlugin::updateSideBarSource
     Q_INVOKABLE virtual void setSource(const QUrl &url) = 0;
-    virtual void scrollToAnchor(const QString &anchor) = 0;
     virtual void highlightId(const QString &id) { Q_UNUSED(id) }
 
     virtual void setHtml(const QString &html) = 0;

src/plugins/help/qtwebkithelpviewer.cpp

@@ -467,16 +467,12 @@ void QtWebKitHelpViewer::setSource(const QUrl &url)
     QUrl newWithoutFragment = url;
     newWithoutFragment.setFragment(QString());
     if (oldWithoutFragment == newWithoutFragment) {
+        m_webView->page()->mainFrame()->scrollToAnchor(url.fragment());
         slotLoadStarted();
         slotLoadFinished();
     }
 }
 
-void QtWebKitHelpViewer::scrollToAnchor(const QString &anchor)
-{
-    m_webView->page()->mainFrame()->scrollToAnchor(anchor);
-}
-
 void QtWebKitHelpViewer::highlightId(const QString &id)
 {
     if (m_oldHighlightId == id)

src/plugins/help/qtwebkithelpviewer.h

@@ -56,7 +56,6 @@ public:
 
     QUrl source() const;
     void setSource(const QUrl &url);
-    void scrollToAnchor(const QString &anchor);
     void highlightId(const QString &id);
 
     void setHtml(const QString &html);

src/plugins/help/textbrowserhelpviewer.cpp

@@ -38,6 +38,8 @@
 #include <QHelpEngine>
 #include <QKeyEvent>
 #include <QMenu>
+#include <QScrollBar>
+#include <QTimer>
 #include <QToolTip>
 #include <QVBoxLayout>
 
@@ -145,12 +147,13 @@ void TextBrowserHelpViewer::setSource(const QUrl &url)
 
     slotLoadStarted();
     m_textBrowser->setSource(url);
-    slotLoadFinished();
-}
-
-void TextBrowserHelpViewer::scrollToAnchor(const QString &anchor)
-{
-    m_textBrowser->scrollToAnchor(anchor);
+    QTimer::singleShot(0, this, [this, url]() {
+        if (!url.fragment().isEmpty())
+            m_textBrowser->scrollToAnchor(url.fragment());
+        if (QScrollBar *hScrollBar = m_textBrowser->horizontalScrollBar())
+            hScrollBar->setValue(0);
+        slotLoadFinished();
+    });
 }
 
 void TextBrowserHelpViewer::setHtml(const QString &html)

src/plugins/help/textbrowserhelpviewer.h

@@ -55,7 +55,6 @@ public:
 
     QUrl source() const;
     void setSource(const QUrl &url);
-    void scrollToAnchor(const QString &anchor);
 
     void setHtml(const QString &html);