[libcalamares] Allow resetting the requirements model

- When a requirements checker starts, it can reset the model
  to clear it of previous entries.

src/libcalamares/modulesystem/RequirementsChecker.cpp

@@ -32,6 +32,7 @@ RequirementsChecker::RequirementsChecker( QVector< Module* > modules, Requiremen
     , m_progressTimer( nullptr )
     , m_progressTimeouts( 0 )
 {
+    m_model->clear();
     m_watchers.reserve( m_modules.count() );
     connect( this, &RequirementsChecker::requirementsProgress, model, &RequirementsModel::setProgressMessage );
 }
@@ -63,9 +64,9 @@ RequirementsChecker::finished()
     static QMutex finishedMutex;
     QMutexLocker lock( &finishedMutex );
 
-    if ( m_progressTimer && std::all_of( m_watchers.cbegin(), m_watchers.cend(), []( const Watcher* w ) {
-             return w && w->isFinished();
-         } ) )
+    if ( m_progressTimer
+         && std::all_of(
+             m_watchers.cbegin(), m_watchers.cend(), []( const Watcher* w ) { return w && w->isFinished(); } ) )
     {
         cDebug() << "All requirements have been checked.";
         if ( m_progressTimer )
@@ -100,14 +101,17 @@ RequirementsChecker::reportProgress()
     m_progressTimeouts++;
 
     QStringList remainingNames;
-    auto remaining = std::count_if( m_watchers.cbegin(), m_watchers.cend(), [&]( const Watcher* w ) {
-        if ( w && !w->isFinished() )
-        {
-            remainingNames << w->objectName();
-            return true;
-        }
-        return false;
-    } );
+    auto remaining = std::count_if( m_watchers.cbegin(),
+                                    m_watchers.cend(),
+                                    [ & ]( const Watcher* w )
+                                    {
+                                        if ( w && !w->isFinished() )
+                                        {
+                                            remainingNames << w->objectName();
+                                            return true;
+                                        }
+                                        return false;
+                                    } );
     if ( remaining > 0 )
     {
         cDebug() << "Remaining modules:" << remaining << Logger::DebugList( remainingNames );

src/libcalamares/modulesystem/RequirementsModel.cpp

@@ -15,6 +15,16 @@
 namespace Calamares
 {
 
+void
+RequirementsModel::clear()
+{
+    QMutexLocker l( &m_addLock );
+    emit beginResetModel();
+    m_requirements.clear();
+    changeRequirementsList();
+    emit endResetModel();
+}
+
 void
 RequirementsModel::addRequirementsList( const Calamares::RequirementsList& requirements )
 {

src/libcalamares/modulesystem/RequirementsModel.h

@@ -77,6 +77,10 @@ signals:
 protected:
     QHash< int, QByteArray > roleNames() const override;
 
+
+    ///@brief Clears the requirements; resets the model
+    void clear();
+
     ///@brief Append some requirements; resets the model
     void addRequirementsList( const Calamares::RequirementsList& requirements );