Revert "Revert "Stabilize ordering graph""

This reverts commit 2b23016a51.

pkg/solver/decoder.go

@@ -163,7 +163,7 @@ func (assertions PackagesAssertions) Order(definitiondb pkg.PackageDatabase, fin
 	// Build a topological graph
 	for _, a := range unorderedAssertions {
 		currentPkg := a.Package
-		added := map[string]interface{}{}
+		added := map[string][]*pkg.DefaultPackage{}
 	REQUIRES:
 		for _, requiredDef := range currentPkg.GetRequires() {
 			if def, err := definitiondb.FindPackage(requiredDef); err == nil { // Provides: Get a chance of being override here
@@ -181,7 +181,16 @@ func (assertions PackagesAssertions) Order(definitiondb pkg.PackageDatabase, fin
 			}
 			// Expand also here, as we need to order them (or instead the solver should give back the dep correctly?)
 			graph.AddEdge(currentPkg.GetFingerPrint(), requiredDef.GetFingerPrint())
-			added[requiredDef.GetFingerPrint()] = nil
+
+			// The following is optional - it doesn't change the "correctness" of the solver results
+			// Here we add an extra edge between deps that share common dependendencies.
+			// This makes the link more stronger and balances the graph so it doesn't show
+			// different results for the same query, as they could be shuffled as don't have a direct connection.
+			for _, d := range added[currentPkg.GetFingerPrint()] {
+				graph.AddEdge(d.GetFingerPrint(), requiredDef.GetFingerPrint())
+			}
+			added[currentPkg.GetFingerPrint()] = append(added[currentPkg.GetFingerPrint()], requiredDef)
+
 		}
 	}
 	result, err := graph.TopSort(fingerprint)

pkg/solver/decoder_test.go

@@ -388,5 +388,37 @@ var _ = Describe("Decoder", func() {
 
 			Expect(solution4.Drop(Y).AssertionHash()).To(Equal(solution4.HashFrom(Y)))
 		})
+		for index := 0; index < 300; index++ { // Just to make sure we don't have false positives
+
+			It("Always same solution", func() {
+
+				X := pkg.NewPackage("X", "", []*pkg.DefaultPackage{}, []*pkg.DefaultPackage{})
+				Y := pkg.NewPackage("Y", "", []*pkg.DefaultPackage{X}, []*pkg.DefaultPackage{})
+				Z := pkg.NewPackage("Z", "", []*pkg.DefaultPackage{X}, []*pkg.DefaultPackage{})
+				W := pkg.NewPackage("W", "", []*pkg.DefaultPackage{Z, Y}, []*pkg.DefaultPackage{})
+
+				for _, p := range []pkg.Package{X, Y, Z} {
+					_, err := dbDefinitions.CreatePackage(p)
+					Expect(err).ToNot(HaveOccurred())
+				}
+
+				for _, p := range []pkg.Package{} {
+					_, err := dbInstalled.CreatePackage(p)
+					Expect(err).ToNot(HaveOccurred())
+				}
+
+				solution, err := s.Install([]pkg.Package{W})
+				Expect(err).ToNot(HaveOccurred())
+
+				orderW, err := solution.Order(dbDefinitions, W.GetFingerPrint())
+				Expect(err).ToNot(HaveOccurred())
+				Expect(orderW[0].Package.GetName()).To(Equal("X"))
+				Expect(orderW[1].Package.GetName()).To(Equal("Y"))
+				Expect(orderW[2].Package.GetName()).To(Equal("Z"))
+				Expect(orderW[3].Package.GetName()).To(Equal("W"))
+			})
+
+		}
+
 	})
 })