[processing] Be more careful with output geometries added as a

result of clipping

(cherry-picked from 6f5405a)

python/plugins/processing/tests/testdata/expected/clip_lines_by_multipolygon.gml

@@ -1,16 +1,16 @@
 <?xml version="1.0" encoding="utf-8" ?>
 <ogr:FeatureCollection
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-     xsi:schemaLocation=""
+     xsi:schemaLocation="http://ogr.maptools.org/ clip_lines_by_multipolygon.xsd"
      xmlns:ogr="http://ogr.maptools.org/"
      xmlns:gml="http://www.opengis.net/gml">
   <gml:boundedBy>
     <gml:Box>
-      <gml:coord><gml:X>2</gml:X><gml:Y>-1</gml:Y></gml:coord>
+      <gml:coord><gml:X>2</gml:X><gml:Y>1</gml:Y></gml:coord>
       <gml:coord><gml:X>8</gml:X><gml:Y>3</gml:Y></gml:coord>
     </gml:Box>
   </gml:boundedBy>
-
+                                                                                                                                                                
   <gml:featureMember>
     <ogr:clip_lines_by_multipolygon fid="lines.2">
       <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>2,1 2,2</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>2,2 3,2</gml:coordinates></gml:LineString></gml:lineStringMember><gml:lineStringMember><gml:LineString><gml:coordinates>3,2 3,3</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
@@ -26,9 +26,4 @@
       <ogr:geometryProperty><gml:MultiLineString srsName="EPSG:4326"><gml:lineStringMember><gml:LineString><gml:coordinates>7,2 8,2</gml:coordinates></gml:LineString></gml:lineStringMember></gml:MultiLineString></ogr:geometryProperty>
     </ogr:clip_lines_by_multipolygon>
   </gml:featureMember>
-  <gml:featureMember>
-    <ogr:clip_lines_by_multipolygon fid="lines.5">
-      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>8,-1</gml:coordinates></gml:Point></ogr:geometryProperty>
-    </ogr:clip_lines_by_multipolygon>
-  </gml:featureMember>
 </ogr:FeatureCollection>

python/plugins/processing/tests/testdata/expected/clip_lines_by_multipolygon.xsd

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema targetNamespace="http://ogr.maptools.org/" xmlns:ogr="http://ogr.maptools.org/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml" elementFormDefault="qualified" version="1.0">
+<xs:import namespace="http://www.opengis.net/gml" schemaLocation="http://schemas.opengis.net/gml/2.1.2/feature.xsd"/>
+<xs:element name="FeatureCollection" type="ogr:FeatureCollectionType" substitutionGroup="gml:_FeatureCollection"/>
+<xs:complexType name="FeatureCollectionType">
+  <xs:complexContent>
+    <xs:extension base="gml:AbstractFeatureCollectionType">
+      <xs:attribute name="lockId" type="xs:string" use="optional"/>
+      <xs:attribute name="scope" type="xs:string" use="optional"/>
+    </xs:extension>
+  </xs:complexContent>
+</xs:complexType>
+<xs:element name="clip_lines_by_multipolygon" type="ogr:clip_lines_by_multipolygon_Type" substitutionGroup="gml:_Feature"/>
+<xs:complexType name="clip_lines_by_multipolygon_Type">
+  <xs:complexContent>
+    <xs:extension base="gml:AbstractFeatureType">
+      <xs:sequence>
+        <xs:element name="geometryProperty" type="gml:MultiLineStringPropertyType" nillable="true" minOccurs="0" maxOccurs="1"/>
+      </xs:sequence>
+    </xs:extension>
+  </xs:complexContent>
+</xs:complexType>
+</xs:schema>

src/analysis/processing/qgsalgorithmclip.cpp

@@ -17,6 +17,7 @@
 
 #include "qgsalgorithmclip.h"
 #include "qgsgeometryengine.h"
+#include "qgsoverlayutils.h"
 
 ///@cond PRIVATE
 
@@ -78,6 +79,7 @@ QVariantMap QgsClipAlgorithm::processAlgorithm( const QVariantMap &parameters, Q
     throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "OVERLAY" ) ) );
 
   QString dest;
+  QgsWkbTypes::GeometryType sinkType = QgsWkbTypes::geometryType( featureSource->wkbType() );
   std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest, featureSource->fields(), QgsWkbTypes::multiType( featureSource->wkbType() ), featureSource->sourceCrs() ) );
 
   if ( !sink )
@@ -184,6 +186,9 @@ QVariantMap QgsClipAlgorithm::processAlgorithm( const QVariantMap &parameters, Q
         newGeometry = inputFeature.geometry();
       }
 
+      if ( !QgsOverlayUtils::sanitizeIntersectionResult( newGeometry, sinkType ) )
+        continue;
+
       QgsFeature outputFeature;
       outputFeature.setGeometry( newGeometry );
       outputFeature.setAttributes( inputFeature.attributes() );

src/analysis/processing/qgsoverlayutils.cpp

@@ -20,8 +20,7 @@
 
 ///@cond PRIVATE
 
-//! Makes sure that what came out from intersection of two geometries is good to be used in the output
-static bool sanitizeIntersectionResult( QgsGeometry &geom, QgsWkbTypes::GeometryType geometryType )
+bool QgsOverlayUtils::sanitizeIntersectionResult( QgsGeometry &geom, QgsWkbTypes::GeometryType geometryType )
 {
   if ( geom.isNull() )
   {

src/analysis/processing/qgsoverlayutils.h

@@ -17,6 +17,7 @@
 #define QGSOVERLAYUTILS_H
 
 #include <QList>
+#include "qgswkbtypes.h"
 
 #define SIP_NO_FILE
 
@@ -27,6 +28,7 @@ class QgsFeatureSink;
 class QgsFields;
 class QgsProcessingContext;
 class QgsProcessingFeedback;
+class QgsGeometry;
 
 namespace QgsOverlayUtils
 {
@@ -43,6 +45,9 @@ namespace QgsOverlayUtils
 
   void intersection( const QgsFeatureSource &sourceA, const QgsFeatureSource &sourceB, QgsFeatureSink &sink, QgsProcessingContext &context, QgsProcessingFeedback *feedback, int &count, int totalCount, const QList<int> &fieldIndicesA, const QList<int> &fieldIndicesB );
 
+  //! Makes sure that what came out from intersection of two geometries is good to be used in the output
+  bool sanitizeIntersectionResult( QgsGeometry &geom, QgsWkbTypes::GeometryType geometryType );
+
   /**
    * Copies features from the source to the sink and resolves overlaps: for each pair of overlapping features A and B
    * it will produce: