fix namegen algo and add more test cases covering corner cases

Author: erenboz

internal/xds/balancer/clusterresolver/configbuilder_childname.go

@@ -66,17 +66,16 @@ func (ng *nameGenerator) generate(priorities [][]xdsresource.Locality) []string
 	for _, priority := range priorities {
 		var nameFound string
 		for _, locality := range priority {
-			if name, ok := ng.currentNames[locality.ID]; ok {
-				if !usedNames[name] {
-					nameFound = name
-					break
-				}
+			if name, ok := ng.currentNames[locality.ID]; ok && !usedNames[name] {
+				nameFound = name
+				break
 			}
 		}
 
-		for _, locality := range priority {
-			if name, ok := ng.firstAssignedNames[locality.ID]; ok {
-				if !usedNames[name] {
+		if nameFound == "" {
+			// If no name found in current names, check first assigned names instead of generating completely new names.
+			for _, locality := range priority {
+				if name, ok := ng.firstAssignedNames[locality.ID]; ok && !usedNames[name] {
 					nameFound = name
 					break
 				}
@@ -95,11 +94,12 @@ func (ng *nameGenerator) generate(priorities [][]xdsresource.Locality) []string
 			}
 		}
 		ret = append(ret, nameFound)
-		usedNames[nameFound] = true
-
+		// All localities in this priority share the same name. Add them all to
+		// the new map.
 		for _, locality := range priority {
 			newNames[locality.ID] = nameFound
 		}
+		usedNames[nameFound] = true
 	}
 	ng.currentNames = newNames
 	return ret

internal/xds/balancer/clusterresolver/configbuilder_childname_test.go

@@ -105,6 +105,35 @@ func Test_nameGenerator_generate(t *testing.T) {
 			},
 			want: []string{"priority-0-0", "priority-0-2", "priority-0-1"},
 		},
+		{
+			name: "split and reverse priority",
+			inputs: [][][]xdsresource.Locality{
+				{
+					{{ID: clients.Locality{Zone: "L0"}}, {ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L0"}}},
+				},
+			},
+			want: []string{"priority-0-0", "priority-0-1"},
+		},
+		{
+			name: "delete and bring back",
+			inputs: [][][]xdsresource.Locality{
+				{
+					{{ID: clients.Locality{Zone: "L0"}}, {ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L1"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L2"}}, {ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L0"}}},
+				},
+			},
+			want: []string{"priority-0-0"},
+		},
 		{
 			name: "complex merge split sequence",
 			inputs: [][][]xdsresource.Locality{
@@ -140,7 +169,7 @@ func Test_nameGenerator_generate(t *testing.T) {
 					{{ID: clients.Locality{Zone: "L3"}}},
 				},
 			},
-			want: []string{"priority-0-0", "priority-0-1", "priority-0-2"},
+			want: []string{"priority-0-0", "priority-0-3", "priority-0-2"},
 		},
 		{
 			name: "complex full merges splits sequence",
@@ -198,7 +227,59 @@ func Test_nameGenerator_generate(t *testing.T) {
 					{{ID: clients.Locality{Zone: "L1"}}},
 				},
 			},
-			want: []string{"priority-0-1", "priority-0-0"},
+			want: []string{"priority-0-0", "priority-0-2"},
+		},
+		{
+			name: "merge-split reverse times 2",
+			inputs: [][][]xdsresource.Locality{
+				{
+					{{ID: clients.Locality{Zone: "L1"}}},
+					{{ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L1"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L1"}}},
+					{{ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L1"}}, {ID: clients.Locality{Zone: "L2"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L1"}}},
+				},
+			},
+			want: []string{"priority-0-2", "priority-0-0"},
+		},
+		{
+			name: "complex merge-split reverse",
+			inputs: [][][]xdsresource.Locality{
+				{
+					{{ID: clients.Locality{Zone: "L1"}}},
+					{{ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L3"}}, {ID: clients.Locality{Zone: "L4"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L1"}}},
+					{{ID: clients.Locality{Zone: "L4"}}, {ID: clients.Locality{Zone: "L2"}}},
+					{{ID: clients.Locality{Zone: "L3"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L2"}}, {ID: clients.Locality{Zone: "L1"}}},
+					{{ID: clients.Locality{Zone: "L4"}}},
+				},
+				{
+					{{ID: clients.Locality{Zone: "L4"}}},
+					{{ID: clients.Locality{Zone: "L1"}}},
+				},
+			},
+			want: []string{"priority-0-4", "priority-0-2"},
 		},
 		{
 			name: "2 by 2 shuffle sequence",