Spec compliance: do not require interfaces to have at least one implementor

graphql/graphql-spec#459

Author: vladar

src/Type/SchemaValidationContext.php

@@ -270,9 +270,6 @@ public function validateTypes()
             } elseif ($type instanceof InterfaceType) {
                 // Ensure fields are valid.
                 $this->validateFields($type);
-
-                // Ensure Interfaces include at least 1 Object type.
-                $this->validateInterfaces($type);
             } elseif ($type instanceof UnionType) {
                 // Ensure Unions include valid member types.
                 $this->validateUnionMembers($type);
@@ -517,23 +514,6 @@ private function validateObjectInterfaces(ObjectType $object)
         }
     }
 
-    private function validateInterfaces(InterfaceType $iface)
-    {
-        $possibleTypes = $this->schema->getPossibleTypes($iface);
-
-        if (count($possibleTypes) !== 0) {
-            return;
-        }
-
-        $this->reportError(
-            sprintf(
-                'Interface %s must be implemented by at least one Object type.',
-                $iface->name
-            ),
-            $iface->astNode
-        );
-    }
-
     /**
      * @param InterfaceType $iface
      *

tests/Type/ValidationTest.php

@@ -1562,7 +1562,7 @@ interface SomeInterface {
     }
 
     /**
-     * @see it('rejects an interface not implemented by at least one object')
+     * @see it('accepts an interface not implemented by at least one object')
      */
     public function testRejectsAnInterfaceNotImplementedByAtLeastOneObject()
     {
@@ -1577,11 +1577,7 @@ interface SomeInterface {
         ');
         $this->assertMatchesValidationMessage(
             $schema->validate(),
-            [[
-                'message' => 'Interface SomeInterface must be implemented by at least one Object type.',
-                'locations' => [[ 'line' => 6, 'column' => 7 ]],
-            ],
-            ]
+            []
         );
     }