Fix(GraphQL): Fix GraphQL encoding in case of empty list (#7726) (#7730)

* Fix output node rewriting in case of null list

* Fix lint

(cherry picked from commit 9e8ab99)

graphql/e2e/common/common.go

@@ -861,7 +861,8 @@ func RunAll(t *testing.T) {
 	t.Run("add multiple mutations", testMultipleMutations)
 	t.Run("deep XID mutations", deepXIDMutations)
 	t.Run("three level xid", testThreeLevelXID)
-	t.Run("nested add mutation with @hasInverse", nestedAddMutationWithHasInverse)
+	t.Run("nested add mutation with multiple linked lists and @hasInverse",
+		nestedAddMutationWithMultipleLinkedListsAndHasInverse)
 	t.Run("add mutation with @hasInverse overrides correctly", addMutationWithHasInverseOverridesCorrectly)
 	t.Run("error in multiple mutations", addMultipleMutationWithOneError)
 	t.Run("dgraph directive with reverse edge adds data correctly",

graphql/e2e/common/mutation.go

@@ -4143,14 +4143,17 @@ func intWithList(t *testing.T) {
 
 }
 
-func nestedAddMutationWithHasInverse(t *testing.T) {
+func nestedAddMutationWithMultipleLinkedListsAndHasInverse(t *testing.T) {
 	params := &GraphQLParams{
 		Query: `mutation addPerson1($input: [AddPerson1Input!]!) {
             addPerson1(input: $input) {
                 person1 {
                     name
                     friends {
                         name
+						closeFriends {
+							name
+						}
                         friends {
                             name
                         }
@@ -4186,6 +4189,7 @@ func nestedAddMutationWithHasInverse(t *testing.T) {
             {
               "friends": [
                 {
+				  "closeFriends": [],
                   "friends": [
                     {
                       "name": "Or"

graphql/e2e/directives/schema.graphql

@@ -207,6 +207,7 @@ type post1{
 type Person1 {
     id: ID!
     name: String!
+    closeFriends: [Person1] @hasInverse(field: closeFriends)
     friends: [Person1] @hasInverse(field: friends)
 }
 

graphql/e2e/directives/schema_response.json

@@ -336,6 +336,11 @@
       "type": "uid",
       "list": true
     },
+    {
+      "predicate": "Person1.closeFriends",
+      "type": "uid",
+      "list": true
+    },
     {
       "predicate": "Person1.name",
       "type": "string"
@@ -1061,6 +1066,9 @@
         },
         {
           "name": "Person1.friends"
+        },
+        {
+          "name": "Person1.closeFriends"
         }
       ],
       "name": "Person1"

graphql/e2e/normal/schema.graphql

@@ -213,6 +213,7 @@ type post1{
 type Person1 {
     id: ID!
     name: String!
+    closeFriends: [Person1] @hasInverse(field: closeFriends)
     friends: [Person1] @hasInverse(field: friends)
 }
 

graphql/e2e/normal/schema_response.json

@@ -422,6 +422,11 @@
       "type": "uid",
       "list": true
     },
+    {
+      "predicate": "Person1.closeFriends",
+      "type": "uid",
+      "list": true
+    },
     {
       "predicate": "Person1.name",
       "type": "string"
@@ -1117,6 +1122,9 @@
         },
         {
           "name": "Person1.friends"
+        },
+        {
+          "name": "Person1.closeFriends"
         }
       ],
       "name": "Person1"

query/outputnode_graphql.go

@@ -444,7 +444,16 @@ func (genc *graphQLEncoder) encode(encInp encodeInput) bool {
 		}
 
 		// Step-3: Update counters and Write closing ] for JSON arrays
-		if !curSelectionIsDgList || next == nil || genc.getAttr(cur) != genc.getAttr(next) {
+		// We perform this step in any of the 4 conditions is satisfied.
+		// 1. The current selection is not a Dgraph List (It's of custom type or a single JSON object)
+		// 2. We are at the end of json encoding process and there is no fastjson node ahead (next == nil)
+		// 3. We are at the end of list writing and the type of next fastJSON node is not equal to
+		//    type of curr fastJSON node.
+		// 4. The current selection set which we are encoding is not equal to the type of
+		//    current fastJSON node.
+		if !curSelectionIsDgList || next == nil ||
+			genc.getAttr(cur) != genc.getAttr(next) ||
+			curSelection.DgraphAlias() != genc.attrForID(genc.getAttr(cur)) {
 			if curSelectionIsDgList && !nullWritten {
 				x.Check2(genc.buf.WriteRune(']'))
 			}