[processing] More helpful errors when raster inputs are not valid

Author: nyalldawson

python/core/processing/qgsprocessingalgorithm.sip.in

@@ -756,6 +756,23 @@ should correspond to the invalid source parameter name.
 
 .. versionadded:: 3.2
 
+.. seealso:: :py:func:`invalidRasterError`
+
+.. seealso:: :py:func:`invalidSinkError`
+%End
+
+    static QString invalidRasterError( const QVariantMap &parameters, const QString &name );
+%Docstring
+Returns a user-friendly string to use as an error when a raster layer input could
+not be loaded.
+
+The ``parameters`` argument should give the algorithms parameter map, and the ``name``
+should correspond to the invalid source parameter name.
+
+.. versionadded:: 3.2
+
+.. seealso:: :py:func:`invalidSourceError`
+
 .. seealso:: :py:func:`invalidSinkError`
 %End
 
@@ -770,6 +787,8 @@ should correspond to the invalid source parameter name.
 .. versionadded:: 3.2
 
 .. seealso:: :py:func:`invalidSourceError`
+
+.. seealso:: :py:func:`invalidRasterError`
 %End
 
   private:

src/analysis/processing/qgsalgorithmrasterlayeruniquevalues.cpp

@@ -77,7 +77,7 @@ bool QgsRasterLayerUniqueValuesReportAlgorithm::prepareAlgorithm( const QVariant
   int band = parameterAsInt( parameters, QStringLiteral( "BAND" ), context );
 
   if ( !layer )
-    return false;
+    throw QgsProcessingException( invalidRasterError( parameters, QStringLiteral( "INPUT" ) ) );
 
   mInterface.reset( layer->dataProvider()->clone() );
   mHasNoDataValue = layer->dataProvider()->sourceHasNoDataValue( band );

src/analysis/processing/qgsalgorithmzonalhistogram.cpp

@@ -77,7 +77,7 @@ bool QgsZonalHistogramAlgorithm::prepareAlgorithm( const QVariantMap &parameters
   mBand = parameterAsInt( parameters, QStringLiteral( "RASTER_BAND" ), context );
 
   if ( !layer )
-    throw QgsProcessingException( QObject::tr( "Could not load raster layer" ) );
+    throw QgsProcessingException( invalidRasterError( parameters, QStringLiteral( "INPUT_RASTER" ) ) );
 
   mInterface.reset( layer->dataProvider()->clone() );
   mHasNoDataValue = layer->dataProvider()->sourceHasNoDataValue( mBand );

src/core/processing/qgsprocessingalgorithm.cpp

@@ -98,6 +98,8 @@ bool QgsProcessingAlgorithm::checkParameterValues( const QVariantMap &parameters
           *message = invalidSourceError( parameters, def->name() );
         else if ( def->type() == QgsProcessingParameterFeatureSink::typeName() )
           *message = invalidSinkError( parameters, def->name() );
+        else if ( def->type() == QgsProcessingParameterRasterLayer::typeName() )
+          *message = invalidRasterError( parameters, def->name() );
         else
           *message = QObject::tr( "Incorrect parameter value for %1" ).arg( def->name() );
       }
@@ -695,6 +697,28 @@ QString QgsProcessingAlgorithm::invalidSourceError( const QVariantMap &parameter
   }
 }
 
+QString QgsProcessingAlgorithm::invalidRasterError( const QVariantMap &parameters, const QString &name )
+{
+  if ( !parameters.contains( name ) )
+    return QObject::tr( "Could not load source layer for %1: no value specified for parameter" ).arg( name );
+  else
+  {
+    QVariant var = parameters.value( name );
+    if ( var.canConvert<QgsProperty>() )
+    {
+      QgsProperty p = var.value< QgsProperty >();
+      if ( p.propertyType() == QgsProperty::StaticProperty )
+      {
+        var = p.staticValue();
+      }
+    }
+    if ( !var.toString().isEmpty() )
+      return QObject::tr( "Could not load source layer for %1: %2 not found" ).arg( name, var.toString() );
+    else
+      return QObject::tr( "Could not load source layer for %1: invalid value" ).arg( name );
+  }
+}
+
 QString QgsProcessingAlgorithm::invalidSinkError( const QVariantMap &parameters, const QString &name )
 {
   if ( !parameters.contains( name ) )

src/core/processing/qgsprocessingalgorithm.h

@@ -753,10 +753,25 @@ class CORE_EXPORT QgsProcessingAlgorithm
      *
      * \since QGIS 3.2
      *
+     * \see invalidRasterError()
      * \see invalidSinkError()
      */
     static QString invalidSourceError( const QVariantMap &parameters, const QString &name );
 
+    /**
+     * Returns a user-friendly string to use as an error when a raster layer input could
+     * not be loaded.
+     *
+     * The \a parameters argument should give the algorithms parameter map, and the \a name
+     * should correspond to the invalid source parameter name.
+     *
+     * \since QGIS 3.2
+     *
+     * \see invalidSourceError()
+     * \see invalidSinkError()
+     */
+    static QString invalidRasterError( const QVariantMap &parameters, const QString &name );
+
     /**
      * Returns a user-friendly string to use as an error when a sink parameter could
      * not be created.
@@ -767,6 +782,7 @@ class CORE_EXPORT QgsProcessingAlgorithm
      * \since QGIS 3.2
      *
      * \see invalidSourceError()
+     * \see invalidRasterError()
      */
     static QString invalidSinkError( const QVariantMap &parameters, const QString &name );
 

tests/src/analysis/testqgsprocessing.cpp

@@ -3423,6 +3423,16 @@ void TestQgsProcessing::parameterRasterLayer()
   // optional with direct layer
   def.reset( new QgsProcessingParameterRasterLayer( "optional", QString(), QVariant::fromValue( r1 ), true ) );
   QCOMPARE( QgsProcessingParameters::parameterAsRasterLayer( def.get(), params, context )->id(), r1->id() );
+
+  // invalidRasterError
+  params.clear();
+  QCOMPARE( QgsProcessingAlgorithm::invalidRasterError( params, QStringLiteral( "MISSING" ) ), QStringLiteral( "Could not load source layer for MISSING: no value specified for parameter" ) );
+  params.insert( QStringLiteral( "INPUT" ), QStringLiteral( "my layer" ) );
+  QCOMPARE( QgsProcessingAlgorithm::invalidRasterError( params, QStringLiteral( "INPUT" ) ), QStringLiteral( "Could not load source layer for INPUT: my layer not found" ) );
+  params.insert( QStringLiteral( "INPUT" ), QgsProperty::fromValue( "my prop layer" ) );
+  QCOMPARE( QgsProcessingAlgorithm::invalidRasterError( params, QStringLiteral( "INPUT" ) ), QStringLiteral( "Could not load source layer for INPUT: my prop layer not found" ) );
+  params.insert( QStringLiteral( "INPUT" ), QVariant::fromValue( v1 ) );
+  QCOMPARE( QgsProcessingAlgorithm::invalidRasterError( params, QStringLiteral( "INPUT" ) ), QStringLiteral( "Could not load source layer for INPUT: invalid value" ) );
 }
 
 void TestQgsProcessing::parameterEnum()