Merge Inline Fragment Nested Interface Fields

codegen/testserver/followschema/interfaces.go

@@ -14,6 +14,7 @@ type ShapeUnion interface {
 
 type Circle struct {
 	Radius float64
+	Coordinates
 }
 
 func (c *Circle) Area() float64 {
@@ -25,6 +26,7 @@ func (c *Circle) isShape()      {}
 
 type Rectangle struct {
 	Length, Width float64
+	Coordinates
 }
 
 func (r *Rectangle) Area() float64 {
@@ -79,6 +81,7 @@ type BackedByInterfaceImpl struct {
 func (b *BackedByInterfaceImpl) ThisShouldBind() string {
 	return b.Value
 }
+
 func (b *BackedByInterfaceImpl) ThisShouldBindWithError() (string, error) {
 	return b.Value, b.Error
 }

codegen/testserver/followschema/interfaces.graphql

@@ -27,19 +27,27 @@ type Cat implements Animal {
     catBreed: String!
 }
 
+type Coordinates {
+    x: Float!
+    y: Float!
+}
 interface Shape {
     area: Float
+    coordinates: Coordinates
 }
+
 type Circle implements Shape {
     radius: Float
     area: Float
+    coordinates: Coordinates
 }
 type Rectangle implements Shape {
     length: Float
     width: Float
     area: Float
+    coordinates: Coordinates
 }
-union ShapeUnion @goModel(model:"followschema.ShapeUnion") = Circle | Rectangle
+union ShapeUnion @goModel(model: "followschema.ShapeUnion") = Circle | Rectangle
 
 directive @makeNil on FIELD_DEFINITION
 directive @makeTypedNil on FIELD_DEFINITION
@@ -55,7 +63,7 @@ type ConcreteNodeA implements Node {
     name: String!
 }
 
-""" Implements the Node interface with another interface """
+" Implements the Node interface with another interface "
 type ConcreteNodeInterface implements Node {
     id: ID!
     child: Node!

codegen/testserver/followschema/interfaces_test.go

@@ -197,4 +197,60 @@ func TestInterfaces(t *testing.T) {
 		require.Equal(t, "CNII", resp.Node.ID)
 		require.Equal(t, "Child", resp.Node.Child.ID)
 	})
+
+	t.Run("interface implementors should return merged base fields", func(t *testing.T) {
+		resolvers := &Stub{}
+		resolvers.QueryResolver.Shapes = func(ctx context.Context) (shapes []Shape, err error) {
+			return []Shape{
+				&Rectangle{
+					Coordinates: Coordinates{
+						X: -1,
+						Y: -1,
+					},
+				},
+				&Circle{
+					Coordinates: Coordinates{
+						X: 1,
+						Y: 1,
+					},
+				},
+			}, nil
+		}
+
+		c := client.New(handler.NewDefaultServer(NewExecutableSchema(Config{Resolvers: resolvers})))
+		var resp struct {
+			Shapes []struct {
+				Coordinates struct {
+					X float64
+					Y float64
+				}
+			}
+		}
+
+		c.MustPost(`
+			{
+				shapes {
+					coordinates {
+						x
+					}
+					... on Rectangle {
+						coordinates {
+							x
+						}
+					}
+					... on Circle {
+						coordinates {
+							y
+						}
+					}
+				}
+			}
+		`, &resp)
+
+		require.Equal(t, 2, len(resp.Shapes))
+		require.Equal(t, float64(-1), resp.Shapes[0].Coordinates.X)
+		require.Equal(t, float64(0), resp.Shapes[0].Coordinates.Y)
+		require.Equal(t, float64(1), resp.Shapes[1].Coordinates.X)
+		require.Equal(t, float64(1), resp.Shapes[1].Coordinates.Y)
+	})
 }