Refactor arg codegen

Now a function is generated for each field and directive that has
arguments. This function can be used by both field methods as well as
the `Complexity` method.

The `args.gotpl` template now generates the code for this function, so
its purpose is a little different than it used to be.

codegen/directive.go

@@ -11,6 +11,14 @@ type Directive struct {
 	Args []FieldArgument
 }
 
+func (d *Directive) ArgsFunc() string {
+	if len(d.Args) == 0 {
+		return ""
+	}
+
+	return "dir_" + d.Name + "_args"
+}
+
 func (d *Directive) CallArgs() string {
 	args := []string{"ctx", "obj", "n"}
 

codegen/object.go

@@ -121,6 +121,14 @@ func (f *Field) ShortInvocation() string {
 	return fmt.Sprintf("%s().%s(%s)", f.Object.GQLType, f.GoNameExported(), f.CallArgs())
 }
 
+func (f *Field) ArgsFunc() string {
+	if len(f.Args) == 0 {
+		return ""
+	}
+
+	return "field_" + f.Object.GQLType + "_" + f.GQLName + "_args"
+}
+
 func (f *Field) ResolverType() string {
 	if !f.IsResolver() {
 		return ""
@@ -247,7 +255,7 @@ func (f *Field) doWriteJson(val string, remainingMods []string, astType *ast.Typ
 			{{.arr}} := make(graphql.Array, len({{.val}}))
 			{{ if and .top (not .isScalar) }} var wg sync.WaitGroup {{ end }}
 			{{ if not .isScalar }}
-				isLen1 := len({{.val}}) == 1 
+				isLen1 := len({{.val}}) == 1
 				if !isLen1 {
 					wg.Add(len({{.val}}))
 				}
@@ -265,7 +273,7 @@ func (f *Field) doWriteJson(val string, remainingMods []string, astType *ast.Typ
 							defer wg.Done()
 						}
 						{{.arr}}[{{.index}}] = func() graphql.Marshaler {
-							{{ .next }} 
+							{{ .next }}
 						}()
 					}
 					if isLen1 {
@@ -275,7 +283,7 @@ func (f *Field) doWriteJson(val string, remainingMods []string, astType *ast.Typ
 					}
 				{{ else }}
 					{{.arr}}[{{.index}}] = func() graphql.Marshaler {
-						{{ .next }} 
+						{{ .next }}
 					}()
 				{{- end}}
 			}

codegen/templates/args.gotpl

@@ -1,17 +1,13 @@
-	{{- if . }}args := map[string]interface{}{} {{end}}
+	args := map[string]interface{}{}
 	{{- range $i, $arg := . }}
 		var arg{{$i}} {{$arg.Signature }}
 		if tmp, ok := rawArgs[{{$arg.GQLName|quote}}]; ok {
 			var err error
 			{{$arg.Unmarshal (print "arg" $i) "tmp" }}
 			if err != nil {
-				ec.Error(ctx, err)
-				{{- if $arg.Stream }}
-					return nil
-				{{- else }}
-					return graphql.Null
-				{{- end }}
+				return nil, err
 			}
 		}
 		args[{{$arg.GQLName|quote}}] = arg{{$i}}
-	{{- end -}}
+	{{- end }}
+	return args, nil

codegen/templates/field.gotpl

@@ -5,7 +5,11 @@
 	func (ec *executionContext) _{{$object.GQLType}}_{{$field.GQLName}}(ctx context.Context, field graphql.CollectedField) func() graphql.Marshaler {
 		{{- if $field.Args }}
 			rawArgs := field.ArgumentMap(ec.Variables)
-			{{ template "args.gotpl" $field.Args }}
+			args, err := {{ $field.ArgsFunc }}(rawArgs)
+			if err != nil {
+				ec.Error(ctx, err)
+				return nil
+			}
 		{{- end }}
 		ctx = graphql.WithResolverContext(ctx, &graphql.ResolverContext{
 			Field: field,
@@ -30,7 +34,11 @@
 	func (ec *executionContext) _{{$object.GQLType}}_{{$field.GQLName}}(ctx context.Context, field graphql.CollectedField, {{if not $object.Root}}obj *{{$object.FullName}}{{end}}) graphql.Marshaler {
 		{{- if $field.Args }}
 			rawArgs := field.ArgumentMap(ec.Variables)
-			{{ template "args.gotpl" $field.Args }}
+			args, err := {{ $field.ArgsFunc }}(rawArgs)
+			if err != nil {
+				ec.Error(ctx, err)
+				return graphql.Null
+			}
 		{{- end }}
 		rctx := &graphql.ResolverContext{
 			Object: {{$object.GQLType|quote}},

codegen/templates/generated.gotpl

@@ -61,6 +61,24 @@ type ComplexityRoot struct {
 	{{- end }}
 {{- end }}
 
+{{ range $object := .Objects -}}
+	{{ range $field := $object.Fields -}}
+		{{ if $field.Args }}
+			func {{ $field.ArgsFunc }}(rawArgs map[string]interface{}) (map[string]interface{}, error) {
+			{{ template "args.gotpl" $field.Args }}
+			}
+		{{ end }}
+	{{ end }}
+{{- end }}
+
+{{ range $directive := .Directives }}
+	{{ if $directive.Args }}
+		func {{ $directive.ArgsFunc }}(rawArgs map[string]interface{}) (map[string]interface{}, error) {
+		{{ template "args.gotpl" $directive.Args }}
+		}
+	{{ end }}
+{{ end }}
+
 type executableSchema struct {
 	resolvers  ResolverRoot
 	directives DirectiveRoot
@@ -211,7 +229,11 @@ func (ec *executionContext) FieldMiddleware(ctx context.Context, obj interface{}
 			if ec.directives.{{$directive.Name|ucFirst}} != nil {
 				{{- if $directive.Args }}
 					rawArgs := d.ArgumentMap(ec.Variables)
-					{{ template "args.gotpl" $directive.Args }}
+					args, err := {{ $directive.ArgsFunc }}(rawArgs)
+					if err != nil {
+						ec.Error(ctx, err)
+						return nil
+					}
 				{{- end }}
 				n := next
 				next = func(ctx context.Context) (interface{}, error) {