A type can specify the same field multiple times

[danielmai]

What version of Dgraph are you using?

v1.1.0

Have you tried reproducing the issue with the latest release?

Yes

Steps to reproduce the issue (command/config used to run Dgraph).

1. Run Dgraph

2. Update the schema with the following type:

   type Person {
     name: string
     name: string
   }
   

3. The schema update is successful and the type contains two fields named name.

   schema(type: Person) {}
   

   {
     "data": {
       "types": [
         {
           "fields": [
             {
               "name": "name",
               "type": "string"
             },
             {
               "name": "name",
               "type": "string"
             }
           ],
           "name": "Person"
         }
       ]
     }
   }
   

Expected behavior and actual result.

This type shouldn't be valid. A way to avoid this would be for the schema update to fail with an error when there are duplicate field names.