[libcalamaresui] Remove *back* button from ViewManager

- Now the back button should be done by clients as well
- Refactor in CalamaresWindow to avoid leaking local button pointers
  to surrounding code.
- Add macro UPDATE_BUTTON_PROPERTY for convenience in ViewManager
  (ugh, macro) to change a value and emit corresponding update signal.

src/calamares/CalamaresWindow.cpp

@@ -164,28 +164,39 @@ QWidget*
 CalamaresWindow::getWidgetNavigation()
 {
     QWidget* navigation = new QWidget( this );
-
-    // Create buttons and sets an initial icon; the icons may change
-    auto* back = new QPushButton( getButtonIcon( QStringLiteral( "go-previous" ) ), tr( "&Back" ), navigation );
-    back->setObjectName( "view-button-back" );
-    connect( back, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::back );
-    auto* next = new QPushButton( getButtonIcon( QStringLiteral( "go-next" ) ), tr( "&Next" ), navigation );
-    next->setObjectName( "view-button-next" );
-    connect( next, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::next );
-    connect( m_viewManager, &Calamares::ViewManager::nextEnabledChanged, next, &QPushButton::setEnabled );
-    connect( m_viewManager, &Calamares::ViewManager::nextLabelChanged, next, &QPushButton::setText );
-    connect(
-        m_viewManager, &Calamares::ViewManager::nextIconChanged, this, [=]( QString n ) { setButtonIcon( next, n ); } );
-    auto* quit = new QPushButton( getButtonIcon( QStringLiteral( "dialog-cancel" ) ), tr( "&Cancel" ), navigation );
-    quit->setObjectName( "view-button-cancel" );
-    connect( quit, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::quit );
-
     QBoxLayout* bottomLayout = new QHBoxLayout;
     bottomLayout->addStretch();
-    bottomLayout->addWidget( back );
+
-    bottomLayout->addWidget( next );
+    // Create buttons and sets an initial icon; the icons may change
+    {
+        auto* back = new QPushButton( getButtonIcon( QStringLiteral( "go-previous" ) ), tr( "&Back" ), navigation );
+        back->setObjectName( "view-button-back" );
+        connect( back, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::back );
+        connect( m_viewManager, &Calamares::ViewManager::backEnabledChanged, back, &QPushButton::setEnabled );
+        connect( m_viewManager, &Calamares::ViewManager::backLabelChanged, back, &QPushButton::setText );
+        connect( m_viewManager, &Calamares::ViewManager::backIconChanged, this, [=]( QString n ) {
+            setButtonIcon( back, n );
+        } );
+        bottomLayout->addWidget( back );
+    }
+    {
+        auto* next = new QPushButton( getButtonIcon( QStringLiteral( "go-next" ) ), tr( "&Next" ), navigation );
+        next->setObjectName( "view-button-next" );
+        connect( next, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::next );
+        connect( m_viewManager, &Calamares::ViewManager::nextEnabledChanged, next, &QPushButton::setEnabled );
+        connect( m_viewManager, &Calamares::ViewManager::nextLabelChanged, next, &QPushButton::setText );
+        connect( m_viewManager, &Calamares::ViewManager::nextIconChanged, this, [=]( QString n ) {
+            setButtonIcon( next, n );
+        } );
+        bottomLayout->addWidget( next );
+    }
     bottomLayout->addSpacing( 12 );
-    bottomLayout->addWidget( quit );
+    {
+        auto* quit = new QPushButton( getButtonIcon( QStringLiteral( "dialog-cancel" ) ), tr( "&Cancel" ), navigation );
+        quit->setObjectName( "view-button-cancel" );
+        connect( quit, &QPushButton::clicked, m_viewManager, &Calamares::ViewManager::quit );
+        bottomLayout->addWidget( quit );
+    }
 
     navigation->setLayout( bottomLayout );
     return navigation;

src/libcalamaresui/ViewManager.cpp

@@ -38,6 +38,12 @@
 #include <QMessageBox>
 #include <QMetaObject>
 
+#define UPDATE_BUTTON_PROPERTY( name, value ) \
+    { \
+        m_##name = value; \
+        emit name##Changed( m_##name ); \
+    }
+
 namespace Calamares
 {
 
@@ -89,8 +95,6 @@ ViewManager::ViewManager( QObject* parent )
     mainLayout->addWidget( m_stack );
 
     // Create buttons and sets an initial icon; the icons may change
-    m_back = new QPushButton( getButtonIcon( QStringLiteral( "go-previous" ) ), tr( "&Back" ), m_widget );
-    m_back->setObjectName( "view-button-back" );
     m_quit = new QPushButton( getButtonIcon( QStringLiteral( "dialog-cancel" ) ), tr( "&Cancel" ), m_widget );
     m_quit->setObjectName( "view-button-cancel" );
 
@@ -99,13 +103,9 @@ ViewManager::ViewManager( QObject* parent )
     QBoxLayout* bottomLayout = new QHBoxLayout;
     mainLayout->addLayout( bottomLayout );
     bottomLayout->addStretch();
-    bottomLayout->addWidget( m_back );
-    bottomLayout->addSpacing( 12 );
     bottomLayout->addWidget( m_quit );
 
-    connect( m_back, &QPushButton::clicked, this, &ViewManager::back );
     connect( m_quit, &QPushButton::clicked, this, &ViewManager::quit );
-    m_back->setEnabled( false );
 
     connect( JobQueue::instance(), &JobQueue::failed, this, &ViewManager::onInstallationFailed );
     connect( JobQueue::instance(), &JobQueue::finished, this, &ViewManager::next );
@@ -363,9 +363,8 @@ ViewManager::next()
         {
             // Reached the end in a weird state (e.g. no finished step after an exec)
             executing = false;
-            m_nextEnabled = false;
+            UPDATE_BUTTON_PROPERTY( nextEnabled, false )
-            emit nextEnabledChanged( m_nextEnabled );
+            UPDATE_BUTTON_PROPERTY( backEnabled, false )
-            m_back->setEnabled( false );
         }
         updateCancelEnabled( !settings->disableCancel() && !( executing && settings->disableCancelDuringExec() ) );
     }
@@ -376,9 +375,8 @@ ViewManager::next()
 
     if ( m_currentStep < m_steps.count() )
     {
-        m_nextEnabled = !executing && m_steps.at( m_currentStep )->isNextEnabled();
+        UPDATE_BUTTON_PROPERTY( nextEnabled, !executing && m_steps.at( m_currentStep )->isNextEnabled() )
-        emit nextEnabledChanged( m_nextEnabled );
+        UPDATE_BUTTON_PROPERTY( backEnabled, !executing && m_steps.at( m_currentStep )->isBackEnabled() )
-        m_back->setEnabled( !executing && m_steps.at( m_currentStep )->isBackEnabled() );
     }
 
     updateButtonLabels();
@@ -400,21 +398,17 @@ ViewManager::updateButtonLabels()
     // If we're going into the execution step / install phase, other message
     if ( stepIsExecute( m_steps, m_currentStep + 1 ) )
     {
-        m_nextLabel = nextIsInstallationStep;
+        UPDATE_BUTTON_PROPERTY( nextLabel, nextIsInstallationStep )
-        m_nextIcon = "run-install";
+        UPDATE_BUTTON_PROPERTY( nextIcon, "run-install" )
-        emit nextLabelChanged( m_nextLabel );
-        emit nextIconChanged( m_nextIcon );
     }
     else
     {
-        m_nextLabel = tr( "&Next" );
+        UPDATE_BUTTON_PROPERTY( nextLabel, tr( "&Next" ) )
-        m_nextIcon = "go-next";
+        UPDATE_BUTTON_PROPERTY( nextIcon, "go-next" )
-        emit nextLabelChanged( m_nextLabel );
-        emit nextIconChanged( m_nextIcon );
     }
 
     // Going back is always simple
-    m_back->setText( tr( "&Back" ) );
+    UPDATE_BUTTON_PROPERTY( backLabel, tr( "&Back" ) )
 
     // Cancel button changes label at the end
     if ( isAtVeryEnd( m_steps, m_currentStep ) )
@@ -465,14 +459,11 @@ ViewManager::back()
         return;
     }
 
-    m_nextEnabled = m_steps.at( m_currentStep )->isNextEnabled();
+    UPDATE_BUTTON_PROPERTY( nextEnabled, m_steps.at( m_currentStep )->isNextEnabled() )
-    emit nextEnabledChanged( m_nextEnabled );
+    UPDATE_BUTTON_PROPERTY( backEnabled,
-    m_back->setEnabled( m_steps.at( m_currentStep )->isBackEnabled() );
+                            ( m_currentStep == 0 && m_steps.first()->isAtBeginning() )
-
+                                ? false
-    if ( m_currentStep == 0 && m_steps.first()->isAtBeginning() )
+                                : m_steps.at( m_currentStep )->isBackEnabled() )
-    {
-        m_back->setEnabled( false );
-    }
 
     updateButtonLabels();
 }

src/libcalamaresui/ViewManager.h

@@ -38,10 +38,15 @@ class UIDLLEXPORT ViewManager : public QAbstractListModel
 {
     Q_OBJECT
     Q_PROPERTY( int currentStepIndex READ currentStepIndex NOTIFY currentStepChanged FINAL )
+
     Q_PROPERTY( bool nextEnabled READ nextEnabled NOTIFY nextEnabledChanged FINAL )
     Q_PROPERTY( QString nextLabel READ nextLabel NOTIFY nextLabelChanged FINAL )
     Q_PROPERTY( QString nextIcon READ nextIcon NOTIFY nextIconChanged FINAL )
 
+    Q_PROPERTY( bool backEnabled READ backEnabled NOTIFY backEnabledChanged FINAL )
+    Q_PROPERTY( QString backLabel READ backLabel NOTIFY backLabelChanged FINAL )
+    Q_PROPERTY( QString backIcon READ backIcon NOTIFY backIconChanged FINAL )
+
 public:
     /**
      * @brief instance access to the ViewManager singleton.
@@ -121,6 +126,18 @@ public Q_SLOTS:
      * have any pages before the current one.
      */
     void back();
+    bool backEnabled() const
+    {
+        return m_backEnabled;  ///< Is the back-button to be enabled
+    }
+    QString backLabel() const
+    {
+        return m_backLabel;  ///< What should be displayed on the back-button
+    }
+    QString backIcon() const
+    {
+        return m_backIcon;  ///< Name of the icon to show
+    }
 
     /**
      * @brief Probably quit
@@ -152,6 +169,10 @@ signals:
     void nextLabelChanged( QString ) const;
     void nextIconChanged( QString ) const;
 
+    void backEnabledChanged( bool ) const;
+    void backLabelChanged( QString ) const;
+    void backIconChanged( QString ) const;
+
 private:
     explicit ViewManager( QObject* parent = nullptr );
     virtual ~ViewManager() override;
@@ -167,13 +188,16 @@ private:
 
     QWidget* m_widget;
     QStackedWidget* m_stack;
-    QPushButton* m_back;
     QPushButton* m_quit;
 
     bool m_nextEnabled = false;
     QString m_nextLabel;
     QString m_nextIcon;  ///< Name of icon to show on button
 
+    bool m_backEnabled = false;
+    QString m_backLabel;
+    QString m_backIcon;
+
 public:
     /** @section Model
      *