Add method to retrieve all features from a QgsProcessingFeatureSource

...even when invalid geometries are present and option is set to
skip invalid or break on invalid.

Some algorithms (e.g. those which repair geometries) need a way
to retrieve all features with invalid geometries, regardless of
the user's settings.

src/core/processing/qgsprocessingutils.cpp

@@ -480,6 +480,22 @@ QgsProcessingFeatureSource::~QgsProcessingFeatureSource()
     delete mSource;
 }
 
+QgsFeatureIterator QgsProcessingFeatureSource::getFeatures( const QgsFeatureRequest &request, Flags flags ) const
+{
+  QgsFeatureRequest req( request );
+  req.setTransformErrorCallback( mTransformErrorCallback );
+
+  if ( flags & FlagSkipGeometryValidityChecks )
+    req.setInvalidGeometryCheck( QgsFeatureRequest::GeometryNoCheck );
+  else
+  {
+    req.setInvalidGeometryCheck( mInvalidGeometryCheck );
+    req.setInvalidGeometryCallback( mInvalidGeometryCallback );
+  }
+
+  return mSource->getFeatures( req );
+}
+
 QgsFeatureIterator QgsProcessingFeatureSource::getFeatures( const QgsFeatureRequest &request ) const
 {
   QgsFeatureRequest req( request );

src/core/processing/qgsprocessingutils.h

@@ -230,6 +230,13 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
 {
   public:
 
+    //! Flags controlling how QgsProcessingFeatureSource fetches features
+    enum Flag
+    {
+      FlagSkipGeometryValidityChecks = 1 << 1, //!< Invalid geometry checks should always be skipped. This flag can be useful for algorithms which always require invalid geometries, regardless of any user settings (e.g. "repair geometry" type algorithms).
+    };
+    Q_DECLARE_FLAGS( Flags, Flag )
+
     /**
      * Constructor for QgsProcessingFeatureSource, accepting an original feature source \a originalSource
      * and processing \a context.
@@ -241,6 +248,13 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
 
     ~QgsProcessingFeatureSource();
 
+    /**
+     * Returns an iterator for the features in the source, respecting the supplied feature \a flags.
+     * An optional \a request can be used to optimise the returned
+     * iterator, eg by restricting the returned attributes or geometry.
+     */
+    QgsFeatureIterator getFeatures( const QgsFeatureRequest &request, Flags flags ) const;
+
     QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) const override;
     QgsCoordinateReferenceSystem sourceCrs() const override;
     QgsFields fields() const override;