Fix #12932 - Send and show layer load errors to user

Author: NathanW2

src/app/qgisapp.cpp

@@ -10021,7 +10021,8 @@ QgsVectorLayer *QgisApp::addVectorLayer( const QString &vectorLayerPath, const Q
   }
   else
   {
-    QString msg = tr( "The layer %1 is not a valid layer and can not be added to the map" ).arg( vectorLayerPath );
+    QString message = layer->dataProvider()->error().message( QgsErrorMessage::Text );
+    QString msg = tr( "The layer %1 is not a valid layer and can not be added to the map. Reason: %2" ).arg( vectorLayerPath ).arg( message );
     messageBar()->pushMessage( tr( "Layer is not valid" ), msg, QgsMessageBar::CRITICAL, messageTimeout() );
 
     delete layer;

src/providers/mssql/qgsmssqlprovider.cpp

@@ -363,6 +363,12 @@ void QgsMssqlProvider::loadMetadata()
   }
 }
 
+void QgsMssqlProvider::setLastError( const QString &error )
+{
+  appendError( error );
+  mLastError = error;
+}
+
 void QgsMssqlProvider::loadFields()
 {
   bool isIdentity = false;

src/providers/mssql/qgsmssqlprovider.h

@@ -207,10 +207,7 @@ class QgsMssqlProvider : public QgsVectorDataProvider
     QString mSqlWhereClause;
 
     // Sets the error messages
-    void setLastError( const QString &error )
-    {
-      mLastError = error;
-    }
+    void setLastError( const QString &error );
 
     static void mssqlWkbTypeAndDimension( QgsWkbTypes::Type wkbType, QString &geometryType, int &dim );
     static QgsWkbTypes::Type getWkbType( const QString &wkbType );