entc/load: better error reporting for import cycles (#3266)

entc/load/testdata/cycle/fakent/fakent.go

@@ -0,0 +1,15 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+// Package fakent fis a fake generated Ent package.
+package fakent
+
+import (
+	"entgo.io/ent"
+	"entgo.io/ent/entc/load/testdata/cycle"
+)
+
+type Hook = ent.Hook
+
+var _ = &cycle.Used{}

entc/load/testdata/cycle/schema.go

@@ -0,0 +1,36 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+package cycle
+
+import (
+	"entgo.io/ent"
+	"entgo.io/ent/entc/load/testdata/cycle/fakent"
+	"entgo.io/ent/schema/field"
+)
+
+// User holds the user schema.
+type User struct {
+	ent.Schema
+}
+
+func (User) Fields() []ent.Field {
+	return []ent.Field{
+		field.JSON("used", &Used{}),
+		field.Enum("e").
+			GoType(Enum(0)),
+	}
+}
+
+type (
+	Used        struct{}
+	NotUsed     struct{}
+	notExported struct{}
+	Enum        int
+)
+
+func (Enum) Values() []string { return nil }
+
+// The cause for cycle.
+var _ fakent.Hook = nil