Merge pull request #95 from facebook/unique-input-fields

[RFC] Move input field uniqueness validator

Author: leebyron

spec/Section 2 -- Language.md

@@ -712,7 +712,6 @@ ObjectValue : { ObjectField+ }
   * Let {inputObject} be a new input object value with no fields.
   * For each {field} in {ObjectField+}
     * Let {name} be {Name} in {field}.
-    * If {inputObject} contains a field named {name} throw Syntax Error.
     * Let {value} be the result of evaluating {Value} in {field}.
     * Add a field to {inputObject} of name {name} containing value {value}.
   * Return {inputObject}

spec/Section 5 -- Validation.md

@@ -1028,6 +1028,31 @@ fragment sentientFragment on Sentient {
 is not valid because there exists no type that implements both {Pet}
 and {Sentient}.
 
+## Values
+
+### Input Object Field Uniqueness
+
+** Formal Specification **
+
+  * For each input object value {inputObject} in the document.
+  * For every {inputField} in {inputObject}
+    * Let {name} be the Name of {inputField}.
+    * Let {fields} be all Input Object Fields named {name} in {inputObject}.
+    * {fields} must be the set containing only {inputField}.
+
+** Explanatory Text **
+
+Input objects must not contain more than one fields of the same name, otherwise
+an amgibuity would exist which includes an ignored portion of syntax.
+
+For example the following query will not pass validation.
+
+```graphql
+{
+  field(arg: { field: true, field: false })
+}
+```
+
 ## Directives
 
 ### Directives Are Defined