[processing] Fix QgsProcessingProvider::isSupportedOutputValue handling

of optional output parameters

Refs #21374

Author: nyalldawson

src/core/processing/qgsprocessingprovider.cpp

@@ -109,12 +109,26 @@ QStringList QgsProcessingProvider::supportedOutputTableExtensions() const
 
 bool QgsProcessingProvider::isSupportedOutputValue( const QVariant &outputValue, const QgsProcessingDestinationParameter *parameter, QgsProcessingContext &context, QString &error ) const
 {
-  QString outputPath = QgsProcessingParameters::parameterAsOutputLayer( parameter, outputValue, context );
   error.clear();
+  QString outputPath = QgsProcessingParameters::parameterAsOutputLayer( parameter, outputValue, context ).trimmed();
+
+  if ( outputPath.isEmpty() )
+  {
+    if ( parameter->flags() & QgsProcessingParameterDefinition::FlagOptional )
+    {
+      return true;
+    }
+    else
+    {
+      error = tr( "Missing parameter value %1" ).arg( parameter->description() );
+      return false;
+    }
+  }
+
   if ( parameter->type() == QgsProcessingParameterVectorDestination::typeName()
        ||  parameter->type() == QgsProcessingParameterFeatureSink::typeName() )
   {
-    if ( outputPath.isEmpty() || outputPath.startsWith( QLatin1String( "memory:" ) ) )
+    if ( outputPath.startsWith( QLatin1String( "memory:" ) ) )
     {
       if ( !supportsNonFileBasedOutput() )
       {
@@ -145,7 +159,7 @@ bool QgsProcessingProvider::isSupportedOutputValue( const QVariant &outputValue,
 
     if ( !supportedOutputVectorLayerExtensions().contains( extension, Qt::CaseInsensitive ) )
     {
-      error = tr( "%1 files are not supported as outputs for this algorithm" ).arg( extension );
+      error = tr( "“.%1” files are not supported as outputs for this algorithm" ).arg( extension );
       return false;
     }
     return true;
@@ -156,7 +170,7 @@ bool QgsProcessingProvider::isSupportedOutputValue( const QVariant &outputValue,
     const QString extension = fi.completeSuffix();
     if ( !supportedOutputRasterLayerExtensions().contains( extension, Qt::CaseInsensitive ) )
     {
-      error = tr( "%1 files are not supported as outputs for this algorithm" ).arg( extension );
+      error = tr( "“.%1” files are not supported as outputs for this algorithm" ).arg( extension );
       return false;
     }
     return true;

tests/src/analysis/testqgsprocessing.cpp

@@ -4867,6 +4867,8 @@ void TestQgsProcessing::parameterVectorOut()
   def.reset( new QgsProcessingParameterVectorDestination( "with_geom", QString(), QgsProcessing::TypeVectorAnyGeometry, QString(), true ) );
   DummyProvider3 provider;
   QString error;
+  QVERIFY( provider.isSupportedOutputValue( QVariant(), def.get(), context, error ) ); // optional
+  QVERIFY( provider.isSupportedOutputValue( QString(), def.get(), context, error ) ); // optional
   QVERIFY( !provider.isSupportedOutputValue( "d:/test.shp", def.get(), context, error ) );
   QVERIFY( !provider.isSupportedOutputValue( "d:/test.SHP", def.get(), context, error ) );
   QVERIFY( !provider.isSupportedOutputValue( "ogr:d:/test.shp", def.get(), context, error ) );
@@ -4875,6 +4877,9 @@ void TestQgsProcessing::parameterVectorOut()
   QVERIFY( provider.isSupportedOutputValue( "d:/test.MIF", def.get(), context, error ) );
   QVERIFY( provider.isSupportedOutputValue( "ogr:d:/test.MIF", def.get(), context, error ) );
   QVERIFY( provider.isSupportedOutputValue( QgsProcessingOutputLayerDefinition( "d:/test.MIF" ), def.get(), context, error ) );
+  def.reset( new QgsProcessingParameterVectorDestination( "with_geom", QString(), QgsProcessing::TypeVectorAnyGeometry, QString(), false ) );
+  QVERIFY( !provider.isSupportedOutputValue( QVariant(), def.get(), context, error ) ); // non-optional
+  QVERIFY( !provider.isSupportedOutputValue( QString(), def.get(), context, error ) ); // non-optional
 
   provider.loadAlgorithms();
   def->mOriginalProvider = &provider;
@@ -4986,6 +4991,8 @@ void TestQgsProcessing::parameterRasterOut()
 
   DummyProvider3 provider;
   QString error;
+  QVERIFY( !provider.isSupportedOutputValue( QVariant(), def.get(), context, error ) );
+  QVERIFY( !provider.isSupportedOutputValue( QString(), def.get(), context, error ) );
   QVERIFY( !provider.isSupportedOutputValue( "d:/test.tif", def.get(), context, error ) );
   QVERIFY( !provider.isSupportedOutputValue( "d:/test.TIF", def.get(), context, error ) );
   QVERIFY( !provider.isSupportedOutputValue( QgsProcessingOutputLayerDefinition( "d:/test.tif" ), def.get(), context, error ) );