Fix boolean filtering in QGIS expressions with WFS layers (#60075)

PR #56369 introduced a regression for WFS layers, because stopping using
'false' and 'true' strings to compare with boolean fields in qgis
expressions, and forcing to use the keywords false and true, it
conflicted with the internal SQLite cache database of WFS layers.

This PR fixes it by storing internal boolean in SQLite cache database in
the right form compatible with QGIS internal functions (i.e. storing '0'
and '1' strings instead of 'true' and 'false' strings).

src/providers/wfs/qgsbackgroundcachedshareddata.cpp

@@ -642,6 +642,8 @@ void QgsBackgroundCachedSharedData::serializeFeatures( QVector<QgsFeatureUniqueI
           }
           cachedFeature.setAttribute( idx, stringValue );
         }
+        else if ( mFields.at( i ).type() == QMetaType::Type::Bool ) // WFS boolean fields are stored as varchar in underlying cache sqlite database
+          cachedFeature.setAttribute( idx, QgsSqliteUtils::quotedValue( QVariant::fromValue( v.toBool() ) ) );
         else if ( QgsWFSUtils::isCompatibleType( static_cast<QMetaType::Type>( v.userType() ), fieldType ) )
           cachedFeature.setAttribute( idx, v );
         else

tests/src/python/test_provider_wfs.py

@@ -6277,6 +6277,7 @@ def testFilteredFeatureRequests(self):
      <element type="gml:MultiPointPropertyType" name="geometry" minOccurs="0" maxOccurs="1"/>
      <element type="int" name="id"/>
      <element type="string" name="name"/>
+     <element type="boolean" name="verified"/>
      <element type="int" name="type" nillable="true"/>
      <element type="decimal" name="elevation" nillable="true"/>
     </sequence>
@@ -6313,6 +6314,7 @@ def testFilteredFeatureRequests(self):
   </qgs:geometry>
   <qgs:id>177</qgs:id>
   <qgs:name>Xxx</qgs:name>
+  <qgs:verified>true</qgs:verified>
   <qgs:elevation_source></qgs:elevation_source>
  </qgs:points>
 </gml:featureMember>
@@ -6344,6 +6346,7 @@ def testFilteredFeatureRequests(self):
   </qgs:geometry>
   <qgs:id>177</qgs:id>
   <qgs:name>Xxx</qgs:name>
+  <qgs:verified>true</qgs:verified>
   <qgs:type xsi:nil="true"></qgs:type>
   <qgs:elevation xsi:nil="true"></qgs:elevation>
  </qgs:points>
@@ -6367,6 +6370,7 @@ def testFilteredFeatureRequests(self):
   </qgs:geometry>
   <qgs:id>5</qgs:id>
   <qgs:name>qgis</qgs:name>
+  <qgs:verified>false</qgs:verified>
   <qgs:type>0</qgs:type>
   <qgs:elevation xsi:nil="true"></qgs:elevation>
  </qgs:points>
@@ -6412,6 +6416,31 @@ def testFilteredFeatureRequests(self):
         self.assertEqual(qgis_feat["name"], "qgis")
         self.assertEqual(other_feat["name"], "Xxx")
 
+        qgis_feat = next(
+            vl.getFeatures(QgsFeatureRequest(QgsExpression('"verified" is true')))
+        )
+        other_feat = next(
+            vl.getFeatures(QgsFeatureRequest(QgsExpression('"verified" is false')))
+        )
+        self.assertEqual(qgis_feat["name"], "Xxx")
+        self.assertEqual(other_feat["name"], "qgis")
+
+        qgis_feat = next(vl.getFeatures(QgsFeatureRequest(QgsExpression('"verified"'))))
+        other_feat = next(
+            vl.getFeatures(QgsFeatureRequest(QgsExpression('not "verified"')))
+        )
+        self.assertEqual(qgis_feat["name"], "Xxx")
+        self.assertEqual(other_feat["name"], "qgis")
+
+        qgis_feat = next(
+            vl.getFeatures(QgsFeatureRequest(QgsExpression('"verified" = true')))
+        )
+        other_feat = next(
+            vl.getFeatures(QgsFeatureRequest(QgsExpression('"verified" = false')))
+        )
+        self.assertEqual(qgis_feat["name"], "Xxx")
+        self.assertEqual(other_feat["name"], "qgis")
+
         form_scope = QgsExpressionContextUtils.formScope(qgis_feat)
         form_exp = QgsExpression("current_value('name') = \"name\"")
         ctx = QgsExpressionContext()