Fix clazy reserve-candidates suggestions

Avoids repeated memory allocations

src/app/qgisapp.cpp

@@ -3860,6 +3860,8 @@ void QgisApp::askUserForGDALSublayers( QgsRasterLayer *layer )
 
   QgsSublayersDialog::LayerDefinitionList layers;
   QStringList names;
+  names.reserve( sublayers.size() );
+  layers.reserve( sublayers.size() );
   for ( int i = 0; i < sublayers.size(); i++ )
   {
     // simplify raster sublayer name - should add a function in gdal provider for this?

src/app/qgsvectorlayerproperties.cpp

@@ -1052,6 +1052,7 @@ void QgsVectorLayerProperties::on_mButtonAddJoin_clicked()
 
   QList<QgsMapLayer*> joinedLayers;
   const QList< QgsVectorJoinInfo >& joins = mLayer->vectorJoins();
+  joinedLayers.reserve( joins.size() );
   for ( int i = 0; i < joins.size(); ++i )
   {
     joinedLayers.append( QgsMapLayerRegistry::instance()->mapLayer( joins[i].joinLayerId ) );

src/core/pal/costcalculator.cpp

@@ -104,6 +104,7 @@ void CostCalculator::setPolygonCandidatesCost( int nblp, QList< LabelPosition* >
   // IMPORTANT - only want to sort first nblp positions. The rest have not had the cost
   // calculated so will have nonsense values
   QList< LabelPosition* > toSort;
+  toSort.reserve( nblp );
   for ( int i = 0; i < nblp; ++i )
   {
     toSort << lPos.at( i );

src/core/qgscolorramp.cpp

@@ -784,6 +784,7 @@ QgsColorRamp* QgsPresetSchemeColorRamp::create( const QgsStringMap& properties )
 QList<QColor> QgsPresetSchemeColorRamp::colors() const
 {
   QList< QColor > l;
+  l.reserve( mColors.count() );
   for ( int i = 0; i < mColors.count(); ++i )
   {
     l << mColors.at( i ).first;

src/core/qgsexpression.cpp

@@ -2589,6 +2589,7 @@ static QVariant fcnOrderParts( const QVariantList& values, const QgsExpressionCo
   QgsExpressionSorter sorter( orderBy );
 
   QList<QgsFeature> partFeatures;
+  partFeatures.reserve( collection->partCount() );
   for ( int i = 0; i < collection->partCount(); ++i )
   {
     f.setGeometry( QgsGeometry( collection->geometryN( i )->clone() ) );

src/core/qgslayerdefinition.cpp

@@ -220,11 +220,12 @@ void QgsLayerDefinition::DependencySorter::init( const QDomDocument& doc )
   QStringList layerIds;
 
   QDomNodeList nl = doc.elementsByTagName( "maplayer" );
+  layerIds.reserve( nl.count() );
+  QVector<QString> deps; //avoid expensive allocation for list for every iteration
   for ( int i = 0; i < nl.count(); i++ )
   {
-    QVector<QString> deps;
+    deps.resize( 0 ); // preserve capacity - don't use clear
     QDomNode node = nl.item( i );
-    QDomElement element = node.toElement();
 
     QString id = node.namedItem( "id" ).toElement().text();
     layerIds << id;

src/core/raster/qgsrasterfilewriter.cpp

@@ -185,6 +185,10 @@ QgsRasterFileWriter::WriterError QgsRasterFileWriter::writeDataRaster( const Qgs
   QList<bool> destHasNoDataValueList;
   QList<double> destNoDataValueList;
   QList<Qgis::DataType> destDataTypeList;
+  destDataTypeList.reserve( nBands );
+  destHasNoDataValueList.reserve( nBands );
+  destNoDataValueList.reserve( nBands );
+
   for ( int bandNo = 1; bandNo <= nBands; bandNo++ )
   {
     QgsRasterNuller *nuller = pipe->nuller();

src/core/symbology-ng/qgsmarkersymbollayer.cpp

@@ -1348,6 +1348,7 @@ bool QgsSimpleMarkerSymbolLayer::writeDxf( QgsDxfExport& e, double mmMapUnitScal
     polygon = t.map( polygon );
 
     QgsPointSequence p;
+    p.reserve( polygon.size() );
     for ( int i = 0; i < polygon.size(); i++ )
       p << QgsPointV2( polygon[i] );
     p << p[0];

src/gui/attributetable/qgsattributetablefiltermodel.cpp

@@ -271,6 +271,7 @@ void QgsAttributeTableFilterModel::setFilteredFeatures( const QgsFeatureIds& ids
 QgsFeatureIds QgsAttributeTableFilterModel::filteredFeatures()
 {
   QgsFeatureIds ids;
+  ids.reserve( rowCount() );
   for ( int i = 0; i < rowCount(); ++i )
   {
     QModelIndex row = index( i, 0 );

src/gui/attributetable/qgsorganizetablecolumnsdialog.cpp

@@ -109,6 +109,7 @@ QgsOrganizeTableColumnsDialog::~QgsOrganizeTableColumnsDialog()
 QgsAttributeTableConfig QgsOrganizeTableColumnsDialog::config() const
 {
   QVector<QgsAttributeTableConfig::ColumnConfig> columns;
+  columns.reserve( mFieldsList->count() );
 
   for ( int i = 0 ; i < mFieldsList->count() ; i++ )
   {

src/gui/editorwidgets/qgsvaluerelationsearchwidgetwrapper.cpp

@@ -272,6 +272,7 @@ void QgsValueRelationSearchWidgetWrapper::initWidget( QWidget* editor )
   else if ( mLineEdit )
   {
     QStringList values;
+    values.reserve( mCache.size() );
     Q_FOREACH ( const ValueRelationItem& i,  mCache )
     {
       values << i.second;

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -141,6 +141,7 @@ void QgsValueRelationWidgetWrapper::initWidget( QWidget* editor )
   else if ( mLineEdit )
   {
     QStringList values;
+    values.reserve( mCache.size() );
     Q_FOREACH ( const ValueRelationItem& i,  mCache )
     {
       values << i.second;

src/gui/qgsdatumtransformdialog.cpp

@@ -151,6 +151,7 @@ QList< int > QgsDatumTransformDialog::selectedDatumTransform()
   QTreeWidgetItem * item = mDatumTransformTreeWidget->currentItem();
   if ( item )
   {
+    list.reserve( 2 );
     for ( int i = 0; i < 2; ++i )
     {
       int transformNr = item->data( i, Qt::UserRole ).toInt();

src/gui/raster/qgsrastertransparencywidget.cpp

@@ -406,6 +406,7 @@ void QgsRasterTransparencyWidget::apply()
     {
       QgsRasterTransparency::TransparentThreeValuePixel myTransparentPixel;
       QList<QgsRasterTransparency::TransparentThreeValuePixel> myTransparentThreeValuePixelList;
+      myTransparentThreeValuePixelList.reserve( tableTransparency->rowCount() );
       for ( int myListRunner = 0; myListRunner < tableTransparency->rowCount(); myListRunner++ )
       {
         myTransparentPixel.red = transparencyCellValue( myListRunner, 0 );
@@ -420,6 +421,7 @@ void QgsRasterTransparencyWidget::apply()
     {
       QgsRasterTransparency::TransparentSingleValuePixel myTransparentPixel;
       QList<QgsRasterTransparency::TransparentSingleValuePixel> myTransparentSingleValuePixelList;
+      myTransparentSingleValuePixelList.reserve( tableTransparency->rowCount() );
       for ( int myListRunner = 0; myListRunner < tableTransparency->rowCount(); myListRunner++ )
       {
         myTransparentPixel.min = transparencyCellValue( myListRunner, 0 );

src/gui/symbology-ng/qgssvgselectorwidget.cpp

@@ -306,6 +306,7 @@ QgsSvgSelectorGroupsModel::QgsSvgSelectorGroupsModel( QObject* parent )
   QStringList svgPaths = QgsApplication::svgPaths();
   QStandardItem *parentItem = invisibleRootItem();
   QStringList parentPaths;
+  parentPaths.reserve( svgPaths.size() );
 
   for ( int i = 0; i < svgPaths.size(); i++ )
   {
@@ -538,7 +539,7 @@ void QgsSvgSelectorWidget::populateList()
 //-- QgsSvgSelectorDialog
 
 QgsSvgSelectorDialog::QgsSvgSelectorDialog( QWidget *parent, Qt::WindowFlags fl,
-    const QDialogButtonBox::StandardButtons& buttons,
+    QDialogButtonBox::StandardButtons buttons,
     Qt::Orientation orientation )
     : QDialog( parent, fl )
 {

src/providers/arcgisrest/qgsafsprovider.cpp

@@ -172,6 +172,7 @@ bool QgsAfsProvider::getFeature( const QgsFeatureId &id, QgsFeature &f, bool fet
   // When fetching from server, fetch all attributes and geometry by default so that we can cache them
   QStringList fetchAttribNames;
   QList<int> fetchAttribIdx;
+  fetchAttribIdx.reserve( mFields.size() );
   for ( int idx = 0, n = mFields.size(); idx < n; ++idx )
   {
     fetchAttribNames.append( mFields.at( idx ).name() );
@@ -183,6 +184,7 @@ bool QgsAfsProvider::getFeature( const QgsFeatureId &id, QgsFeature &f, bool fet
   int startId = ( id / 100 ) * 100;
   int stopId = qMin( startId + 100, mObjectIds.length() );
   QList<quint32> objectIds;
+  objectIds.reserve( stopId );
   for ( int i = startId; i < stopId; ++i )
   {
     objectIds.append( mObjectIds[i] );

src/providers/db2/qgsdb2tablemodel.cpp

@@ -242,6 +242,7 @@ void QgsDb2TableModel::setGeometryTypesForTable( QgsDb2LayerProperty layerProper
 
     QList<QStandardItem *> row;
 
+    row.reserve( dbtmColumns );
     for ( int j = 0; j < dbtmColumns; j++ )
     {
       row << itemFromIndex( currentChildIndex.sibling( i, j ) );

src/providers/mssql/qgsmssqltablemodel.cpp

@@ -241,6 +241,7 @@ void QgsMssqlTableModel::setGeometryTypesForTable( QgsMssqlLayerProperty layerPr
     }
 
     QList<QStandardItem *> row;
+    row.reserve( dbtmColumns );
 
     for ( int j = 0; j < dbtmColumns; j++ )
     {

src/providers/wcs/qgswcsprovider.cpp

@@ -272,6 +272,8 @@ QgsWcsProvider::QgsWcsProvider( const QString& uri )
   // Get types
   // TODO: we are using the same data types like GDAL (not wider like GDAL provider)
   // with expectation to replace 'no data' values by NaN
+  mSrcGdalDataType.reserve( mBandCount );
+  mGdalDataType.reserve( mBandCount );
   for ( int i = 1; i <= mBandCount; i++ )
   {
     GDALRasterBandH gdalBand = GDALGetRasterBand( mCachedGdalDataset, i );

src/server/qgsserverprojectparser.cpp

@@ -47,6 +47,7 @@ QgsServerProjectParser::QgsServerProjectParser( QDomDocument* xmlDoc, const QStr
     QDomNodeList layerNodeList = mXMLDoc->elementsByTagName( "maplayer" );
     QDomElement currentElement;
     int nNodes = layerNodeList.size();
+    mProjectLayerElements.reserve( nNodes );
     for ( int i = 0; i < nNodes; ++i )
     {
       currentElement = layerNodeList.at( i ).toElement();
@@ -1470,6 +1471,7 @@ QList< QPair< QString, QgsLayerCoordinateTransform > > QgsServerProjectParser::l
   }
 
   QDomNodeList layerTransformNodeList = coordTransformInfoElem.elementsByTagName( "layer_coordinate_transform" );
+  layerTransformList.reserve( layerTransformNodeList.size() );
   for ( int i = 0; i < layerTransformNodeList.size(); ++i )
   {
     QPair< QString, QgsLayerCoordinateTransform > layerEntry;

src/server/qgswmsprojectparser.cpp

@@ -996,6 +996,7 @@ void QgsWmsProjectParser::addDrawingOrder( QDomElement& parentElem, QDomDocument
   if ( !layerList.isEmpty() )
   {
     QStringList reversedList;
+    reversedList.reserve( layerList.size() );
     for ( int i = layerList.size() - 1; i >= 0; --i )
       reversedList << layerList[ i ];