[processing] Always report errors if features cannot be written

to a destination

Before we silently ignored these - now algorithms will automatically
push errors to the log if a feature cannot be written to a sink (no
changes to algorithms or special handling required)

python/core/processing/qgsprocessingutils.sip.in

@@ -283,6 +283,7 @@ Returns an expression context scope suitable for this source.
 
 
 
+
 /************************************************************************
  * This file has been generated automatically from                      *
  *                                                                      *

src/core/processing/qgsprocessingutils.cpp

@@ -388,7 +388,7 @@ QgsFeatureSink *QgsProcessingUtils::createFeatureSink( QString &destination, Qgs
     destination = layer->id();
 
     // this is a factory, so we need to return a proxy
-    std::unique_ptr< QgsProxyFeatureSink > sink( new QgsProxyFeatureSink( layer->dataProvider() ) );
+    std::unique_ptr< QgsProcessingFeatureSink > sink( new QgsProcessingFeatureSink( layer->dataProvider(), destination, context ) );
     context.temporaryLayerStore()->addMapLayer( layer.release() );
 
     return sink.release();
@@ -415,7 +415,7 @@ QgsFeatureSink *QgsProcessingUtils::createFeatureSink( QString &destination, Qgs
         throw QgsProcessingException( QObject::tr( "Could not create layer %1: %2" ).arg( destination, writer->errorMessage() ) );
       }
       destination = finalFileName;
-      return writer.release();
+      return new QgsProcessingFeatureSink( writer.release(), destination, context, true );
     }
     else
     {
@@ -434,7 +434,7 @@ QgsFeatureSink *QgsProcessingUtils::createFeatureSink( QString &destination, Qgs
       destination = layer->id();
 
       context.temporaryLayerStore()->addMapLayer( layer.release() );
-      return exporter.release();
+      return new QgsProcessingFeatureSink( exporter.release(), destination, context, true );
     }
   }
   return nullptr;
@@ -750,3 +750,44 @@ QgsExpressionContextScope *QgsProcessingFeatureSource::createExpressionContextSc
   }
   return expressionContextScope;
 }
+
+
+//
+// QgsProcessingFeatureSink
+//
+QgsProcessingFeatureSink::QgsProcessingFeatureSink( QgsFeatureSink *originalSink, const QString &sinkName, QgsProcessingContext &context, bool ownsOriginalSink )
+  : QgsProxyFeatureSink( originalSink )
+  , mContext( context )
+  , mSinkName( sinkName )
+  , mOwnsSink( ownsOriginalSink )
+{}
+
+QgsProcessingFeatureSink::~QgsProcessingFeatureSink()
+{
+  if ( mOwnsSink )
+    delete destinationSink();
+}
+
+bool QgsProcessingFeatureSink::addFeature( QgsFeature &feature, QgsFeatureSink::Flags flags )
+{
+  bool result = QgsProxyFeatureSink::addFeature( feature, flags );
+  if ( !result )
+    mContext.feedback()->reportError( QObject::tr( "Feature could not be written to %1" ).arg( mSinkName ) );
+  return result;
+}
+
+bool QgsProcessingFeatureSink::addFeatures( QgsFeatureList &features, QgsFeatureSink::Flags flags )
+{
+  bool result = QgsProxyFeatureSink::addFeatures( features, flags );
+  if ( !result )
+    mContext.feedback()->reportError( QObject::tr( "%1 feature(s) could not be written to %2" ).arg( features.count() ).arg( mSinkName ) );
+  return result;
+}
+
+bool QgsProcessingFeatureSink::addFeatures( QgsFeatureIterator &iterator, QgsFeatureSink::Flags flags )
+{
+  bool result = !QgsProxyFeatureSink::addFeatures( iterator, flags );
+  if ( !result )
+    mContext.feedback()->reportError( QObject::tr( "Features could not be written to %2" ).arg( mSinkName ) );
+  return result;
+}

src/core/processing/qgsprocessingutils.h

@@ -336,6 +336,48 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
 
 };
 
+#ifndef SIP_RUN
+
+/**
+ * \class QgsProcessingFeatureSink
+ * \ingroup core
+ * QgsProxyFeatureSink subclass which reports feature addition errors to a QgsProcessingContext.
+ * \since QGIS 3.0
+ * \note Not available in Python bindings.
+ */
+class CORE_EXPORT QgsProcessingFeatureSink : public QgsProxyFeatureSink
+{
+  public:
+
+
+    /**
+     * Constructor for QgsProcessingFeatureSink, accepting an original feature sink \a originalSink
+     * and processing \a context. Any added features are added to the \a originalSink, with feature
+     * writing errors being reports to \a context.
+     *
+     * The \a context must exist for the lifetime of this object.
+     *
+     * The \a sinkName is used to identify the destination sink when reporting errors.
+     *
+     * Ownership of \a originalSink is dictated by \a ownsOriginalSource. If \a ownsOriginalSink is false,
+     * ownership is not transferred, and callers must ensure that \a originalSink exists for the lifetime of this object.
+     * If \a ownsOriginalSink is true, then this object will take ownership of \a originalSink.
+     */
+    QgsProcessingFeatureSink( QgsFeatureSink *originalSink, const QString &sinkName, QgsProcessingContext &context, bool ownsOriginalSink = false );
+    ~QgsProcessingFeatureSink();
+    bool addFeature( QgsFeature &feature, QgsFeatureSink::Flags flags = nullptr ) override;
+    bool addFeatures( QgsFeatureList &features, QgsFeatureSink::Flags flags = nullptr ) override;
+    bool addFeatures( QgsFeatureIterator &iterator, QgsFeatureSink::Flags flags = nullptr ) override;
+
+  private:
+
+    QgsProcessingContext &mContext;
+    QString mSinkName;
+    bool mOwnsSink = false;
+
+};
+#endif
+
 #endif // QGSPROCESSINGUTILS_H