Support interface unexported methods

codegen/codegen.go

@@ -2,8 +2,8 @@ package codegen
 
 import (
 	"bytes"
-	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -140,7 +140,7 @@ func write(filename string, b []byte) error {
 
 	formatted, err := gofmt(filename, b)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "gofmt failed: %s\n", err.Error())
+		stdErrLog.Printf("gofmt failed: %s\n", err.Error())
 		formatted = b
 	}
 
@@ -151,3 +151,7 @@ func write(filename string, b []byte) error {
 
 	return nil
 }
+
+var (
+	stdErrLog = log.New(os.Stderr, "", log.LstdFlags)
+)

codegen/interface_build.go

@@ -3,7 +3,6 @@ package codegen
 import (
 	"fmt"
 	"go/types"
-	"os"
 	"sort"
 	"strings"
 
@@ -78,9 +77,9 @@ func (cfg *Config) isValueReceiver(intf *NamedType, implementor *NamedType, prog
 	for i := 0; i < interfaceType.NumMethods(); i++ {
 		intfMethod := interfaceType.Method(i)
 
-		implMethod := findMethod(implementorType, intfMethod.Name())
+		implMethod := findMethod(implementorType, intfMethod.Name(), false)
 		if implMethod == nil {
-			fmt.Fprintf(os.Stderr, "missing method %s on %s\n", intfMethod.Name(), implementor.GoType)
+			stdErrLog.Printf("missing method %s on %s\n", intfMethod.Name(), implementor.GoType)
 			return false
 		}
 

codegen/interface_test.go

@@ -1,8 +1,10 @@
 package codegen
 
 import (
+	"strings"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/tools/go/loader"
 )
@@ -36,6 +38,40 @@ func TestShapes(t *testing.T) {
 
 }
 
+func TestInterfaceUnexportedMethods(t *testing.T) {
+	var buf strings.Builder
+	stdErrLog.SetOutput(&buf)
+	err := generate("recursiveinput", `
+			schema {
+				query: Query
+			}
+			
+			type Query {
+			    entities: [Entity!]
+			}
+			
+			interface Entity {
+			    id: ID!
+			}
+			
+			type Foo implements Entity {
+			    id: ID!
+				x: String!
+			}
+			
+			type Bar implements Entity {
+			    id: ID!
+				y: String!
+			}
+	`, TypeMap{
+		"Bar":    {Model: "github.com/vektah/gqlgen/codegen/testdata.IfaceBar"},
+		"Entity": {Model: "github.com/vektah/gqlgen/codegen/testdata.IfaceEntity"},
+		"Foo":    {Model: "github.com/vektah/gqlgen/codegen/testdata.IfaceFoo"},
+	})
+	require.NoError(t, err)
+	assert.Equal(t, "", buf.String(), "using an interface with unexported methods should not emit warnings")
+}
+
 func generate(name string, schema string, typemap ...TypeMap) error {
 	cfg := Config{
 		SchemaStr: schema,

codegen/testdata/iface_models.go

@@ -0,0 +1,19 @@
+package testdata
+
+type IfaceBar struct {
+	ID string `json:"id"`
+	Y  string `json:"y"`
+}
+
+func (IfaceBar) isEntity() {}
+
+type IfaceEntity interface {
+	isEntity() // nolint: megacheck
+}
+
+type IfaceFoo struct {
+	ID string `json:"id"`
+	X  string `json:"x"`
+}
+
+func (IfaceFoo) isEntity() {}

codegen/util.go

@@ -74,10 +74,10 @@ func findGoInterface(prog *loader.Program, pkgName string, typeName string) (*ty
 	return underlying, nil
 }
 
-func findMethod(typ *types.Named, name string) *types.Func {
+func findMethod(typ *types.Named, name string, onlyExported bool) *types.Func {
 	for i := 0; i < typ.NumMethods(); i++ {
 		method := typ.Method(i)
-		if !method.Exported() {
+		if !method.Exported() && onlyExported {
 			continue
 		}
 
@@ -94,7 +94,7 @@ func findMethod(typ *types.Named, name string) *types.Func {
 			}
 
 			if named, ok := field.Type().(*types.Named); ok {
-				if f := findMethod(named, name); f != nil {
+				if f := findMethod(named, name, onlyExported); f != nil {
 					return f
 				}
 			}
@@ -194,7 +194,7 @@ func bindMethod(imports *Imports, t types.Type, field *Field) error {
 		return fmt.Errorf("not a named type")
 	}
 
-	method := findMethod(namedType, field.GQLName)
+	method := findMethod(namedType, field.GQLName, true)
 	if method == nil {
 		return fmt.Errorf("no method named %s", field.GQLName)
 	}