Detect circular references in sketches, and add corresponding tests (#11716)

* Possible fix for 10482 circular reference regression with tests

* Remove redundant test

* Cleanup pre PR

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/Mod/Part/parttests/regression_tests.py

@@ -1,4 +1,4 @@
-from FreeCAD import Vector
+from FreeCAD import Vector, newDocument, closeDocument
 import Part
 
 import unittest
@@ -23,3 +23,27 @@ class RegressionTests(unittest.TestCase):
     def test_OptimalBox(self):
         box = Part.makeBox(1, 1, 1)
         self.assertTrue(box.optimalBoundingBox(True, False).isValid())
+
+    def test_CircularReference(self):
+        # put me in def setup(self): ?
+        self.Doc = newDocument("TestSketchExpr")
+
+        cube = self.Doc.addObject("Part::Box","Cube")
+        cube.setExpression('Length', 'Width + 10mm')
+        with self.assertRaises(RuntimeError) as context:
+            cube.setExpression('Width', 'Length + 10mm')
+        assert "Width reference creates a cyclic dependency." in str(context.exception)
+
+        cube.setExpression('.Placement.Base.x', '.Placement.Base.y + 10mm')
+        with self.assertRaises(RuntimeError) as context:
+            cube.setExpression('.Placement.Base.y', '.Placement.Base.x + 10mm')
+        assert ".Placement.Base.y reference creates a cyclic dependency." in str(context.exception)
+
+        cube.recompute()
+        v1 = cube.Placement.Base
+        cube.recompute()
+        assert cube.Placement.Base.isEqual(v1,1e-6)
+
+        # Put me in def tearDown(self): ?
+        closeDocument(self.Doc.Name)
+

src/Mod/Sketcher/SketcherTests/TestSketchExpression.py

@@ -57,12 +57,26 @@ class TestSketchExpression(unittest.TestCase):
         sketch.addConstraint(conList)
         del geoList, conList
 
+        # Check that circular references get detected
         length = sketch.addConstraint(Sketcher.Constraint("Distance", 0, 6.0))
         height = sketch.addConstraint(Sketcher.Constraint("Distance", 3, 5.0))
-
         sketch.renameConstraint(length, "Length")
+        sketch.renameConstraint(height, "Height")
+
         sketch.setExpression("Constraints[{}]".format(height), ".Constraints.Length")
 
+        with self.assertRaises(RuntimeError) as context:
+            sketch.setExpression("Constraints.Length", ".Constraints.Length * 2")
+        assert ".Constraints.Length reference creates a cyclic dependency." in str(
+            context.exception
+        )
+
+        with self.assertRaises(RuntimeError) as context:
+            sketch.setExpression("Constraints.Length", ".Constraints.Height * 2")
+        assert ".Constraints.Length reference creates a cyclic dependency." in str(
+            context.exception
+        )
+
     def tearDown(self):
         # comment out to omit closing document for debugging
         FreeCAD.closeDocument(self.Doc.Name)