helper/schema: zero value of a set should be empty

helper/schema/resource_data_test.go

@@ -961,6 +961,32 @@ func TestResourceDataGetOk(t *testing.T) {
 			Value: 0,
 			Ok:    false,
 		},
+
+		{
+			Schema: map[string]*Schema{
+				"ports": &Schema{
+					Type:     TypeSet,
+					Optional: true,
+					Elem:     &Schema{Type: TypeInt},
+					Set:      func(a interface{}) int { return a.(int) },
+				},
+			},
+
+			State: nil,
+
+			Diff: &terraform.InstanceDiff{
+				Attributes: map[string]*terraform.ResourceAttrDiff{
+					"ports.#": &terraform.ResourceAttrDiff{
+						Old: "0",
+						New: "0",
+					},
+				},
+			},
+
+			Key:   "ports",
+			Value: []interface{}{},
+			Ok:    false,
+		},
 	}
 
 	for i, tc := range cases {

helper/schema/schema.go

@@ -1084,3 +1084,29 @@ func (m schemaMap) validateType(
 		return m.validatePrimitive(k, raw, schema, c)
 	}
 }
+
+// Zero returns the zero value for a type.
+func (t ValueType) Zero() interface{} {
+	switch t {
+	case TypeInvalid:
+		return nil
+	case TypeBool:
+		return false
+	case TypeInt:
+		return 0
+	case TypeFloat:
+		return 0.0
+	case TypeString:
+		return ""
+	case TypeList:
+		return []interface{}{}
+	case TypeMap:
+		return map[string]interface{}{}
+	case TypeSet:
+		return new(Set)
+	case typeObject:
+		return map[string]interface{}{}
+	default:
+		panic(fmt.Sprintf("unknown type %s", t))
+	}
+}

helper/schema/schema_test.go

@@ -111,7 +111,7 @@ func TestValueType_Zero(t *testing.T) {
 		{TypeString, ""},
 		{TypeList, []interface{}{}},
 		{TypeMap, map[string]interface{}{}},
-		{TypeSet, nil},
+		{TypeSet, new(Set)},
 	}
 
 	for i, tc := range cases {

helper/schema/valuetype.go

@@ -2,8 +2,6 @@ package schema
 
 //go:generate stringer -type=ValueType valuetype.go
 
-import "fmt"
-
 // ValueType is an enum of the type that can be represented by a schema.
 type ValueType int
 
@@ -19,28 +17,5 @@ const (
 	typeObject
 )
 
-// Zero returns the zero value for a type.
-func (t ValueType) Zero() interface{} {
-	switch t {
-	case TypeInvalid:
-		return nil
-	case TypeBool:
-		return false
-	case TypeInt:
-		return 0
-	case TypeFloat:
-		return 0.0
-	case TypeString:
-		return ""
-	case TypeList:
-		return []interface{}{}
-	case TypeMap:
-		return map[string]interface{}{}
-	case TypeSet:
-		return nil
-	case typeObject:
-		return map[string]interface{}{}
-	default:
-		panic(fmt.Sprintf("unknown type %s", t))
-	}
-}
+// NOTE: ValueType has more functions defined on it in schema.go. We can't
+// put them here because we reference other files.