codegen: allow binding methods with optional variadic arguments

codegen/args.go

@@ -73,11 +73,15 @@ func (b *builder) buildArg(obj *Object, arg *ast.ArgumentDefinition) (*FieldArgu
 	return &newArg, nil
 }
 
-func (b *builder) bindArgs(field *Field, params *types.Tuple) ([]*FieldArgument, error) {
-	var newArgs []*FieldArgument
-
+func (b *builder) bindArgs(field *Field, sig *types.Signature, params *types.Tuple) ([]*FieldArgument, error) {
+	n := params.Len()
+	newArgs := make([]*FieldArgument, 0, len(field.Args))
+	// Accept variadic methods (i.e. have optional parameters).
+	if params.Len() > len(field.Args) && sig.Variadic() {
+		n = len(field.Args)
+	}
 nextArg:
-	for j := 0; j < params.Len(); j++ {
+	for j := 0; j < n; j++ {
 		param := params.At(j)
 		for _, oldArg := range field.Args {
 			if strings.EqualFold(oldArg.Name, param.Name()) {

codegen/field.go

@@ -179,8 +179,8 @@ func (b *builder) bindField(obj *Object, f *Field) (errret error) {
 			params = types.NewTuple(vars...)
 		}
 
-		// Try to match target function's arguments with GraphQL field arguments
-		newArgs, err := b.bindArgs(f, params)
+		// Try to match target function's arguments with GraphQL field arguments.
+		newArgs, err := b.bindArgs(f, sig, params)
 		if err != nil {
 			return fmt.Errorf("%s:%d: %w", pos.Filename, pos.Line, err)
 		}

codegen/testserver/followschema/resolver.go

@@ -320,6 +320,10 @@ func (r *queryResolver) ValidType(ctx context.Context) (*ValidType, error) {
 	panic("not implemented")
 }
 
+func (r *queryResolver) VariadicModel(ctx context.Context) (*VariadicModel, error) {
+	panic("not implemented")
+}
+
 func (r *queryResolver) WrappedStruct(ctx context.Context) (*WrappedStruct, error) {
 	panic("not implemented")
 }

codegen/testserver/followschema/variadic.go

@@ -0,0 +1,14 @@
+package followschema
+
+import (
+	"context"
+	"strconv"
+)
+
+type VariadicModel struct{}
+
+type VariadicModelOption func(*VariadicModel)
+
+func (v VariadicModel) Value(ctx context.Context, rank int, opts ...VariadicModelOption) (string, error) {
+	return strconv.Itoa(rank), nil
+}

codegen/testserver/followschema/variadic.graphql

@@ -0,0 +1,7 @@
+extend type Query {
+    variadicModel: VariadicModel
+}
+
+type VariadicModel {
+    value(rank: Int!): String
+}