Add a better error message when passing a type into an input

.gitignore

@@ -3,3 +3,4 @@
 /docs/public
 /example/chat/node_modules
 /example/chat/package-lock.json
+/codegen/tests/gen

codegen/build.go

@@ -41,7 +41,10 @@ func (cfg *Config) models() (*ModelBuild, error) {
 
 	cfg.bindTypes(imports, namedTypes, cfg.modelDir, prog)
 
-	models := cfg.buildModels(namedTypes, prog)
+	models, err := cfg.buildModels(namedTypes, prog)
+	if err != nil {
+		return nil, err
+	}
 	return &ModelBuild{
 		PackageName: cfg.ModelPackageName,
 		Models:      models,

codegen/codegen.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"syscall"
 
 	"github.com/pkg/errors"
 	"github.com/vektah/gqlgen/codegen/templates"
@@ -36,6 +37,9 @@ func Generate(cfg Config) error {
 		return err
 	}
 
+	_ = syscall.Unlink(cfg.ExecFilename)
+	_ = syscall.Unlink(cfg.ModelFilename)
+
 	modelsBuild, err := cfg.models()
 	if err != nil {
 		return errors.Wrap(err, "model plan failed")

codegen/models_build.go

@@ -8,14 +8,17 @@ import (
 	"golang.org/x/tools/go/loader"
 )
 
-func (cfg *Config) buildModels(types NamedTypes, prog *loader.Program) []Model {
+func (cfg *Config) buildModels(types NamedTypes, prog *loader.Program) ([]Model, error) {
 	var models []Model
 
 	for _, typ := range cfg.schema.Types {
 		var model Model
 		switch typ := typ.(type) {
 		case *schema.Object:
-			obj := cfg.buildObject(types, typ)
+			obj, err := cfg.buildObject(types, typ)
+			if err != nil {
+				return nil, err
+			}
 			if obj.Root || obj.IsUserDefined {
 				continue
 			}
@@ -43,7 +46,7 @@ func (cfg *Config) buildModels(types NamedTypes, prog *loader.Program) []Model {
 		return strings.Compare(models[i].GQLType, models[j].GQLType) == -1
 	})
 
-	return models
+	return models, nil
 }
 
 func (cfg *Config) obj2Model(obj *Object) Model {

codegen/object_build.go

@@ -4,6 +4,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/pkg/errors"
 	"github.com/vektah/gqlgen/neelance/schema"
 	"golang.org/x/tools/go/loader"
 )
@@ -14,7 +15,10 @@ func (cfg *Config) buildObjects(types NamedTypes, prog *loader.Program, imports
 	for _, typ := range cfg.schema.Types {
 		switch typ := typ.(type) {
 		case *schema.Object:
-			obj := cfg.buildObject(types, typ)
+			obj, err := cfg.buildObject(types, typ)
+			if err != nil {
+				return nil, err
+			}
 
 			def, err := findGoType(prog, obj.Package, obj.GoType)
 			if err != nil {
@@ -35,7 +39,7 @@ func (cfg *Config) buildObjects(types NamedTypes, prog *loader.Program, imports
 	return objects, nil
 }
 
-func (cfg *Config) buildObject(types NamedTypes, typ *schema.Object) *Object {
+func (cfg *Config) buildObject(types NamedTypes, typ *schema.Object) (*Object, error) {
 	obj := &Object{NamedType: types[typ.TypeName()]}
 
 	for _, i := range typ.Interfaces {
@@ -51,6 +55,10 @@ func (cfg *Config) buildObject(types NamedTypes, typ *schema.Object) *Object {
 				Object:  obj,
 			}
 
+			if !newArg.Type.IsInput && !newArg.Type.IsScalar {
+				return nil, errors.Errorf("%s cannot be used as argument of %s.%s. only input and scalar types are allowed", arg.Type, obj.GQLType, field.Name)
+			}
+
 			if arg.Default != nil {
 				newArg.Default = arg.Default.Value(nil)
 				newArg.StripPtr()
@@ -80,5 +88,5 @@ func (cfg *Config) buildObject(types NamedTypes, typ *schema.Object) *Object {
 			obj.Stream = true
 		}
 	}
-	return obj
+	return obj, nil
 }

codegen/tests/input_union_test.go

@@ -0,0 +1,24 @@
+package tests
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/vektah/gqlgen/codegen"
+)
+
+func TestInputUnion(t *testing.T) {
+	err := codegen.Generate(codegen.Config{
+		SchemaStr: `
+			type Query {
+				addBookmark(b: Bookmarkable!): Boolean!
+			}
+			type Item {}
+			union Bookmarkable = Item
+		`,
+		ExecFilename:  "gen/inputunion/exec.go",
+		ModelFilename: "gen/inputunion/model.go",
+	})
+
+	require.EqualError(t, err, "model plan failed: Bookmarkable! cannot be used as argument of Query.addBookmark. only input and scalar types are allowed")
+}

main.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
-	"syscall"
 
 	"github.com/vektah/gqlgen/codegen"
 )
@@ -38,9 +37,6 @@ func main() {
 		os.Exit(1)
 	}
 
-	_ = syscall.Unlink(*output)
-	_ = syscall.Unlink(*models)
-
 	types := loadTypeMap()
 
 	err = codegen.Generate(codegen.Config{