Avoid 'array compared against 0' error for QgsRasterLayer constructor

... by explicitly passing QString arguments. Otherwise the string
literals are implictly converted to bool and the wrong constructor
is called.

This is not an ideal solution as the API is still misleading, but I
can't see an alternative solution without breaking API and making
one of the constructors explicit or changing their signature.

Author: nyalldawson

src/core/raster/qgsrasterlayer.h

@@ -196,6 +196,11 @@ class CORE_EXPORT QgsRasterLayer : public QgsMapLayer
                     const QString &  baseName = QString::null,
                     bool loadDefaultStyleFlag = true );
 
+    //TODO - QGIS 3.0
+    //This constructor is confusing if used with string literals for providerKey,
+    //as the previous constructor will be called with the literal for providerKey
+    //implicitly converted to a bool.
+    //for QGIS 3.0, make either constructor explicit or alter the signatures
     /**  \brief [ data provider interface ] Constructor in provider mode */
     QgsRasterLayer( const QString & uri,
                     const QString & baseName,

src/gui/qgsrasterformatsaveoptionswidget.cpp

@@ -310,7 +310,7 @@ QString QgsRasterFormatSaveOptionsWidget::validateOptions( bool gui, bool report
       settings.setValue( "/Projections/defaultBehaviour", "useProject" );
     }
     tmpLayer = true;
-    rasterLayer = new QgsRasterLayer( mRasterFileName, QFileInfo( mRasterFileName ).baseName(), "gdal" );
+    rasterLayer = new QgsRasterLayer( mRasterFileName, QFileInfo( mRasterFileName ).baseName(), QString( "gdal" ) );
     // restore /Projections/defaultBehaviour
     if ( defaultProjectionOption == "prompt" )
     {

tests/src/core/testqgslegendrenderer.cpp

@@ -127,7 +127,7 @@ void TestQgsLegendRenderer::init()
 
   static char raster_array[] = { 1, 2, 2, 1 };
   QString rasterUri = QString( "MEM:::DATAPOINTER=%1,PIXELS=2,LINES=2" ).arg(( qulonglong ) raster_array );
-  mRL = new QgsRasterLayer( rasterUri, "Raster Layer", "gdal" );
+  mRL = new QgsRasterLayer( rasterUri, QString( "Raster Layer" ), QString( "gdal" ) );
   QgsMapLayerRegistry::instance()->addMapLayer( mRL );
 
   QgsCategoryList cats;

tests/src/core/testziplayer.cpp

@@ -110,7 +110,7 @@ QgsMapLayer *TestZipLayer::getLayer( QString myPath, QString myName, QString myP
   }
   else if ( myProviderKey == "gdal" )
   {
-    myLayer = new QgsRasterLayer( myPath, myName, "gdal" );
+    myLayer = new QgsRasterLayer( myPath, myName, QString( "gdal" ) );
   }
   // item should not have other provider key, but if it does will return NULL