[processing] Fixes for field calculator and field mapper

- respect project distance, area and ellipsoid settings
- ensure expression variables are correctly evaluated

(cherry-picked from d32c41a)

Author: nyalldawson

python/plugins/processing/algs/qgis/FieldsCalculator.py

@@ -26,7 +26,7 @@
 __revision__ = '$Format:%H$'
 
 from PyQt4.QtCore import QVariant
-from qgis.core import QgsExpression, QgsFeature, QgsField, QgsDistanceArea, QgsProject, GEO_NONE
+from qgis.core import QgsExpression, QgsExpressionContext, QgsExpressionContextUtils, QgsFeature, QgsField, QgsDistanceArea, QgsProject, GEO_NONE
 from qgis.utils import iface
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
@@ -111,8 +111,15 @@ def processAlgorithm(self, progress):
         da.setEllipsoid(QgsProject.instance().readEntry(
             'Measure', '/Ellipsoid', GEO_NONE)[0])
         exp.setGeomCalculator(da)
+        exp.setDistanceUnits(QgsProject.instance().distanceUnits())
+        exp.setAreaUnits(QgsProject.instance().areaUnits())
 
-        if not exp.prepare(layer.pendingFields()):
+        exp_context = QgsExpressionContext()
+        exp_context.appendScope(QgsExpressionContextUtils.globalScope())
+        exp_context.appendScope(QgsExpressionContextUtils.projectScope())
+        exp_context.appendScope(QgsExpressionContextUtils.layerScope(layer))
+
+        if not exp.prepare(exp_context):
             raise GeoAlgorithmExecutionException(
                 self.tr('Evaluation error: %s' % exp.evalErrorString()))
 
@@ -129,8 +136,9 @@ def processAlgorithm(self, progress):
         rownum = 1
         for current, f in enumerate(features):
             rownum = current + 1
-            exp.setCurrentRowNumber(rownum)
-            value = exp.evaluate(f)
+            exp_context.setFeature(f)
+            exp_context.lastScope().setVariable("row_number", rownum)
+            value = exp.evaluate(exp_context)
             if exp.hasEvalError():
                 calculationSuccess = False
                 error = exp.evalErrorString()

python/plugins/processing/algs/qgis/FieldsMapper.py

@@ -26,7 +26,8 @@
 __revision__ = '$Format:%H$'
 
 
-from qgis.core import QgsField, QgsExpression, QgsFeature
+from qgis.core import QgsField, QgsExpression, QgsExpressionContext, QgsExpressionContextUtils, QgsDistanceArea, QgsProject, QgsFeature, GEO_NONE
+from qgis.utils import iface
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
 from processing.core.parameters import ParameterVector
@@ -68,19 +69,36 @@ def processAlgorithm(self, progress):
         provider = layer.dataProvider()
         fields = []
         expressions = []
+
+        da = QgsDistanceArea()
+        da.setSourceCrs(layer.crs().srsid())
+        da.setEllipsoidalMode(
+            iface.mapCanvas().mapSettings().hasCrsTransformEnabled())
+        da.setEllipsoid(QgsProject.instance().readEntry(
+            'Measure', '/Ellipsoid', GEO_NONE)[0])
+
+        exp_context = QgsExpressionContext()
+        exp_context.appendScope(QgsExpressionContextUtils.globalScope())
+        exp_context.appendScope(QgsExpressionContextUtils.projectScope())
+        exp_context.appendScope(QgsExpressionContextUtils.layerScope(layer))
+
         for field_def in mapping:
             fields.append(QgsField(name=field_def['name'],
                                    type=field_def['type'],
                                    len=field_def['length'],
                                    prec=field_def['precision']))
 
             expression = QgsExpression(field_def['expression'])
+            expression.setGeomCalculator(da)
+            expression.setDistanceUnits(QgsProject.instance().distanceUnits())
+            expression.setAreaUnits(QgsProject.instance().areaUnits())
+
             if expression.hasParserError():
                 raise GeoAlgorithmExecutionException(
                     self.tr(u'Parser error in expression "{}": {}')
                     .format(unicode(field_def['expression']),
                             unicode(expression.parserErrorString())))
-            expression.prepare(provider.fields())
+            expression.prepare(exp_context)
             if expression.hasEvalError():
                 raise GeoAlgorithmExecutionException(
                     self.tr(u'Evaluation error in expression "{}": {}')
@@ -108,8 +126,9 @@ def processAlgorithm(self, progress):
             for i in xrange(0, len(mapping)):
                 field_def = mapping[i]
                 expression = expressions[i]
-                expression.setCurrentRowNumber(rownum)
-                value = expression.evaluate(inFeat)
+                exp_context.setFeature(inFeat)
+                exp_context.lastScope().setVariable("row_number", rownum)
+                value = expression.evaluate(exp_context)
                 if expression.hasEvalError():
                     calculationSuccess = False
                     error = expression.evalErrorString()

python/plugins/processing/algs/qgis/ui/FieldsCalculatorDialog.py

@@ -31,6 +31,7 @@
 from PyQt4 import uic
 from PyQt4.QtCore import Qt, QSettings
 from PyQt4.QtGui import QDialog, QFileDialog, QApplication, QCursor, QMessageBox
+from qgis.core import QgsExpressionContext, QgsExpressionContextUtils
 from qgis.gui import QgsEncodingFileDialog
 
 from processing.core.ProcessingConfig import ProcessingConfig
@@ -95,6 +96,14 @@ def updateLayer(self):
         self.builder.setLayer(self.layer)
         self.builder.loadFieldNames()
 
+        exp_context = QgsExpressionContext()
+        exp_context.appendScope(QgsExpressionContextUtils.globalScope())
+        exp_context.appendScope(QgsExpressionContextUtils.projectScope())
+        exp_context.appendScope(QgsExpressionContextUtils.layerScope(self.layer))
+        exp_context.lastScope().setVariable("row_number", 1)
+        exp_context.setHighlightedVariables(["row_number"])
+        self.builder.setExpressionContext(exp_context)
+
         self.populateFields()
 
     def setupSpinboxes(self, index):