Relax to type assignability for values passed to Call.Return.

gomock/call.go

@@ -61,10 +61,16 @@ func (c *Call) Return(rets ...interface{}) *Call {
 			c.receiver, c.method, len(rets), mt.NumOut())
 	}
 	for i, ret := range rets {
-		// TODO: Relax this to permit assignable types. That will require changes to the
-		// generated code, too, because the type assertions there enforce type identity.
-		if got, want := reflect.TypeOf(ret), mt.Out(i); got != want {
-			c.t.Fatalf("wrong type of argument %d to Return for %T.%v: got %v, want %v",
+		if got, want := reflect.TypeOf(ret), mt.Out(i); got == want {
+			// Identical types; nothing to do.
+		} else if got.AssignableTo(want) {
+			// Assignable type relation. Make the assignment now so that the generated code
+			// can return the values with a type assertion.
+			v := reflect.New(want).Elem()
+			v.Set(reflect.ValueOf(ret))
+			rets[i] = v.Interface()
+		} else {
+			c.t.Fatalf("wrong type of argument %d to Return for %T.%v: %v is not assignable to %v",
 				i, c.receiver, c.method, got, want)
 		}
 	}

sample/mock_user/mock_user.go

@@ -134,6 +134,16 @@ func (_mr *_MockIndexRecorder) NillableRet() *gomock.Call {
 	return _mr.mock.ctrl.RecordCall(_mr.mock, "NillableRet")
 }
 
+func (_m *MockIndex) ConcreteRet() chan<- bool {
+	ret := _m.ctrl.Call(_m, "ConcreteRet")
+	ret0, _ := ret[0].(chan<- bool)
+	return ret0
+}
+
+func (_mr *_MockIndexRecorder) ConcreteRet() *gomock.Call {
+	return _mr.mock.ctrl.RecordCall(_mr.mock, "ConcreteRet")
+}
+
 func (_m *MockIndex) Ellip(fmt string, args ...interface{}) {
 	_s := []interface{}{fmt}
 	for _, _x := range args {

sample/user.go

@@ -42,6 +42,8 @@ type Index interface {
 
 	// A method that returns a nillable type.
 	NillableRet() error
+	// A method that returns a non-interface type.
+	ConcreteRet() chan<- bool
 
 	// Methods with an ellipsis argument.
 	Ellip(fmt string, args ...interface{})

sample/user_test.go

@@ -5,9 +5,9 @@ import (
 	"testing"
 
 	"github.com/dsymonds/gomock/gomock"
+	"github.com/dsymonds/gomock/sample"
 	"github.com/dsymonds/gomock/sample/imp1"
 	"github.com/dsymonds/gomock/sample/mock_user"
-	"github.com/dsymonds/gomock/sample"
 )
 
 func TestRemember(t *testing.T) {
@@ -20,6 +20,10 @@ func TestRemember(t *testing.T) {
 
 	// NillableRet returns error. Not declaring it should result in a nil return.
 	mockIndex.EXPECT().NillableRet()
+	// A call that returns something assignable to the return type.
+	// In this case, "chan bool" is assignable to "chan<- bool".
+	boolc := make(chan bool)
+	mockIndex.EXPECT().ConcreteRet().Return(boolc)
 
 	// Should be able to place expectations on variadic methods.
 	mockIndex.EXPECT().Ellip("%d", 0, 1, 1, 2, 3) // direct args
@@ -28,6 +32,10 @@ func TestRemember(t *testing.T) {
 	mockIndex.EXPECT().EllipOnly(gomock.Eq("arg"))
 
 	user.Remember(mockIndex, []string{"a", "b"}, []interface{}{1, 2})
+	// Force checking of the second NillableRet.
+	if c := mockIndex.ConcreteRet(); c != boolc {
+		t.Errorf("ConcreteRet: got %v, want %v", c, boolc)
+	}
 
 	// Try one with an action.
 	calledString := ""