fix #241

Similar to #407, but adds test cases.

Author: sqs

example/social/introspect.json

@@ -214,6 +214,39 @@
         "name": "Pagination",
         "possibleTypes": null
       },
+      {
+        "description": null,
+        "enumValues": null,
+        "fields": [
+          {
+            "args": [],
+            "deprecationReason": null,
+            "description": null,
+            "isDeprecated": false,
+            "name": "name",
+            "type": {
+              "kind": "NON_NULL",
+              "name": null,
+              "ofType": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              }
+            }
+          }
+        ],
+        "inputFields": null,
+        "interfaces": null,
+        "kind": "INTERFACE",
+        "name": "Person",
+        "possibleTypes": [
+          {
+            "kind": "OBJECT",
+            "name": "User",
+            "ofType": null
+          }
+        ]
+      },
       {
         "description": null,
         "enumValues": null,
@@ -545,6 +578,11 @@
             "kind": "INTERFACE",
             "name": "Admin",
             "ofType": null
+          },
+          {
+            "kind": "INTERFACE",
+            "name": "Person",
+            "ofType": null
           }
         ],
         "kind": "OBJECT",

example/social/social.go

@@ -27,9 +27,13 @@ const Schema = `
 		role: Role!
 	}
 
+	interface Person {
+		name: String!
+	}
+
 	scalar Time	
 
-	type User implements Admin {
+	type User implements Admin & Person {
 		id: ID!
 		name: String!
 		email: String!
@@ -64,6 +68,15 @@ type admin interface {
 	Role() string
 }
 
+type adminResolver struct {
+	admin
+}
+
+func (r *adminResolver) ToUser() (*user, bool) {
+	n, ok := r.admin.(user)
+	return &n, ok
+}
+
 type searchResult struct {
 	result interface{}
 }
@@ -189,14 +202,14 @@ type Resolver struct{}
 func (r *Resolver) Admin(ctx context.Context, args struct {
 	ID   string
 	Role string
-}) (admin, error) {
+}) (*adminResolver, error) {
 	if usr, ok := usersMap[args.ID]; ok {
 		if usr.RoleField == args.Role {
-			return *usr, nil
+			return &adminResolver{*usr}, nil
 		}
 	}
 	err := fmt.Errorf("user with id=%s and role=%s does not exist", args.ID, args.Role)
-	return user{}, err
+	return nil, err
 }
 
 func (r *Resolver) User(ctx context.Context, args struct{ Id string }) (user, error) {

graphql_test.go

@@ -1703,6 +1703,52 @@ func TestInlineFragments(t *testing.T) {
 				}
 			`,
 		},
+
+		{
+			Schema: starwarsSchema,
+			Query: `
+				query CharacterSearch {
+					search(text: "C-3PO") {
+						... on Character {
+							name
+						}
+					}
+				}
+			`,
+			ExpectedResult: `
+				{
+					"search": [
+						{
+							"name": "C-3PO"
+						}
+					]
+				}
+			`,
+		},
+
+		{
+			Schema: socialSchema,
+			Query: `
+				query {
+					admin(id: "0x01") {
+						... on User {
+							email
+						}
+						... on Person {
+							name
+						}
+					}
+				}
+			`,
+			ExpectedResult: `
+				{
+					"admin": {
+						"email": "Albus@hogwarts.com",
+						"name": "Albus Dumbledore"
+					}
+				}
+			`,
+		},
 	})
 }
 

internal/exec/selected/selected.go

@@ -173,7 +173,9 @@ func applySelectionSet(r *Request, s *resolvable.Schema, e *resolvable.Object, s
 }
 
 func applyFragment(r *Request, s *resolvable.Schema, e *resolvable.Object, frag *query.Fragment) []Selection {
-	if frag.On.Name != "" && frag.On.Name != e.Name {
+	t := r.Schema.Resolve(frag.On.Name)
+	face, ok := t.(*schema.Interface)
+	if !ok && frag.On.Name != "" && frag.On.Name != e.Name {
 		a, ok := e.TypeAssertions[frag.On.Name]
 		if !ok {
 			panic(fmt.Errorf("%q does not implement %q", frag.On, e.Name)) // TODO proper error handling
@@ -184,6 +186,25 @@ func applyFragment(r *Request, s *resolvable.Schema, e *resolvable.Object, frag
 			Sels:          applySelectionSet(r, s, a.TypeExec.(*resolvable.Object), frag.Selections),
 		}}
 	}
+	if ok && len(face.PossibleTypes) > 0 {
+		sels := []Selection{}
+		for _, t := range face.PossibleTypes {
+			if t.Name == e.Name {
+				return applySelectionSet(r, s, e, frag.Selections)
+			}
+
+			if a, ok := e.TypeAssertions[t.Name]; ok {
+				sels = append(sels, &TypeAssertion{
+					TypeAssertion: *a,
+					Sels:          applySelectionSet(r, s, a.TypeExec.(*resolvable.Object), frag.Selections),
+				})
+			}
+		}
+		if len(sels) == 0 {
+			panic(fmt.Errorf("%q does not implement %q", e.Name, frag.On)) // TODO proper error handling
+		}
+		return sels
+	}
 	return applySelectionSet(r, s, e, frag.Selections)
 }
 

introspection_test.go

@@ -11,6 +11,8 @@ import (
 	"github.com/graph-gophers/graphql-go/example/starwars"
 )
 
+var socialSchema = graphql.MustParseSchema(social.Schema, &social.Resolver{}, graphql.UseFieldResolvers())
+
 func TestSchema_ToJSON(t *testing.T) {
 	t.Parallel()
 
@@ -27,7 +29,7 @@ func TestSchema_ToJSON(t *testing.T) {
 	}{
 		{
 			Name: "Social Schema",
-			Args: args{Schema: graphql.MustParseSchema(social.Schema, &social.Resolver{}, graphql.UseFieldResolvers())},
+			Args: args{Schema: socialSchema},
 			Want: want{JSON: mustReadFile("example/social/introspect.json")},
 		},
 		{