Part::Thickness: This fixes issue #2876 by changing property type for value to include a unit.

src/Mod/Part/App/PartFeatures.cpp

@@ -491,6 +491,9 @@ Thickness::Thickness()
     Join.setEnums(JoinEnums);
     ADD_PROPERTY_TYPE(Intersection,(false),"Thickness",App::Prop_None,"Intersection");
     ADD_PROPERTY_TYPE(SelfIntersection,(false),"Thickness",App::Prop_None,"Self Intersection");
+
+    // Value should have length as unit
+    Value.setUnit(Base::Unit::Length);
 }
 
 short Thickness::mustExecute() const
@@ -510,6 +513,17 @@ short Thickness::mustExecute() const
     return 0;
 }
 
+void Thickness::handleChangedPropertyType(Base::XMLReader &reader, const char *TypeName, App::Property *prop)
+{
+    if (prop == &Value && strcmp(TypeName, "App::PropertyFloat") == 0) {
+        App::PropertyFloat v;
+
+        v.Restore(reader);
+
+        Value.setValue(v.getValue());
+    }
+}
+
 App::DocumentObjectExecReturn *Thickness::execute(void)
 {
     App::DocumentObject* source = Faces.getValue();

src/Mod/Part/App/PartFeatures.h

@@ -123,7 +123,7 @@ public:
     Thickness();
 
     App::PropertyLinkSub Faces;
-    App::PropertyFloat Value;
+    App::PropertyQuantity Value;
     App::PropertyEnumeration Mode;
     App::PropertyEnumeration Join;
     App::PropertyBool Intersection;
@@ -139,6 +139,9 @@ public:
     }
     //@}
 
+protected:
+    void handleChangedPropertyType(Base::XMLReader &reader, const char *TypeName, App::Property *prop);
+
 private:
     static const char* ModeEnums[];
     static const char* JoinEnums[];

src/Mod/Part/TestPartApp.py

@@ -21,6 +21,7 @@
 
 import FreeCAD, os, sys, unittest, Part
 import copy 
+from FreeCAD import Units
 App = FreeCAD
 
 #---------------------------------------------------------------------------
@@ -90,6 +91,26 @@ class PartTestBSplineCurve(unittest.TestCase):
         # spline.setOrigin(2)   # not working?
         self.spline.setPole(1, App.Vector([1, 0, 0])) # first parameter 0 gives occ error
 
+    def testIssue2876(self):
+        self.Doc = App.newDocument("Issue2876")
+        Cylinder = self.Doc.addObject("Part::Cylinder", "Cylinder")
+        Cylinder.Radius = 5
+        Pipe = self.Doc.addObject("Part::Thickness", "Pipe")
+        Pipe.Faces = (Cylinder, ["Face2", "Face3"])
+        Pipe.Mode = 1
+        Pipe.Value = -1 # negative wall thickness
+        Spreadsheet = self.Doc.addObject('Spreadsheet::Sheet', 'Spreadsheet')
+        Spreadsheet.set('A1', 'Pipe OD')
+        Spreadsheet.set('B1', 'Pipe WT')
+        Spreadsheet.set('C1', 'Pipe ID')
+        Spreadsheet.set('A2', '=2*Cylinder.Radius')
+        Spreadsheet.set('B2', '=-Pipe.Value')
+        Spreadsheet.set('C2', '=2*(Cylinder.Radius + Pipe.Value)')
+        self.Doc.recompute()
+        self.assertEqual(Spreadsheet.B2, Units.Quantity('1 mm'))
+        self.assertEqual(Spreadsheet.C2, Units.Quantity('8 mm'))
+        App.closeDocument("Issue2876")
+
     def tearDown(self):
         #closing doc
         FreeCAD.closeDocument("PartTest")

src/Mod/Spreadsheet/TestSpreadsheet.py

@@ -495,7 +495,7 @@ class SpreadsheetCases(unittest.TestCase):
         self.doc.addObject("Part::Thickness", "Pipe")
         sheet.set('B1', '101')
         sheet.set('A53', '=-(-(B1-1)/2)')
-        sheet.set('A54', '=-(Cylinder.Radius + Pipe.Value*1mm - 1"/2)')
+        sheet.set('A54', '=-(Cylinder.Radius + Pipe.Value - 1"/2)')
 
         self.doc.recompute()
         self.assertEqual(sheet.getContents("A1"), "=1 < 2 ? 3 : 4")