change behavior of param cascade to allow parent's cascade (with or w/o param) to trickle to child until overridden explicitly (#6283)

Author: parasssh

query/query.go

@@ -553,9 +553,9 @@ func treeCopy(gq *gql.GraphQuery, sg *SubGraph) error {
 			IsInternal:   gchild.IsInternal,
 		}
 
-		// If parent has @cascade (with or without params), inherit @cascade (with no params)
+		// Inherit from the parent.
 		if len(sg.Params.Cascade) > 0 {
-			args.Cascade = append(args.Cascade, "__all__")
+			args.Cascade = append(args.Cascade, sg.Params.Cascade...)
 		}
 		// Allow over-riding at this level.
 		if len(gchild.Cascade) > 0 {

systest/queries_test.go

@@ -1147,18 +1147,28 @@ func CascadeParams(t *testing.T, c *dgo.Dgraph) {
 			out: `
 			{
 				"q": [
-				  {
-					"name": "Alice 1",
-					"age": "23"
-				  },
-				  {
-					"name": "Alice 2"
-				  },
-				  {
-					"name": "Alice 3",
-					"age": "32"
-				  }
-				]
+					{
+					  "name": "Alice 1",
+					  "age": "23",
+					  "friend": [
+						{
+						  "name": "Bob"
+						}
+					  ]
+					},
+					{
+					  "name": "Alice 2",
+					  "friend": [
+						{
+						  "name": "Chris"
+						}
+					  ]
+					},
+					{
+					  "name": "Alice 3",
+					  "age": "32"
+					}
+				  ]
 			}
 			`,
 		},