Change type notation to HCL2 type annotation

Fixes #9

Terraform v0.12 introduced a new `SchemaConfigModeAttr` feature.
Most attributes have simple types, but if `SchemaConfigModeAttr` is set for
an attribute, it is syntactically NestedBlock but semantically interpreted
as an Attribute. In this case, Attribute has a complex data type. It is
reasonable to use the same notation as the type annotation in HCL2 to
represent the correct data type. However, it seems that HCL2 has a type
annotation parser but no writer, so we implement it by ourselves.

See also:
- #9
- hashicorp/terraform-provider-aws#8187
- hashicorp/terraform#20626
- https://www.terraform.io/docs/configuration/types.html

This is a breaking change caused by the upstream,
so I think it is impossible to maintain tfschema backward compatibility.
I tried to be as consistent as possible.

tfschema/type.go

@@ -1,6 +1,8 @@
 package tfschema
 
 import (
+	"fmt"
+	"sort"
 	"strings"
 
 	"github.com/zclconf/go-cty/cty"
@@ -30,11 +32,99 @@ func (t *Type) MarshalJSON() ([]byte, error) {
 }
 
 // Name returns a name of type.
-// This method customize cty.GoString() to make it easy to read.
+// Terraform v0.12 introduced a new `SchemaConfigModeAttr` feature.
+// Most attributes have simple types, but if `SchemaConfigModeAttr` is set for
+// an attribute, it is syntactically NestedBlock but semantically interpreted
+// as an Attribute. In this case, Attribute has a complex data type. It is
+// reasonable to use the same notation as the type annotation in HCL2 to
+// represent the correct data type. However, it seems that HCL2 has a type
+// annotation parser but no writer, so we implement it by ourselves.
+//
+// See also:
+// - https://github.com/minamijoyo/tfschema/issues/9
+// - https://github.com/terraform-providers/terraform-provider-aws/pull/8187
+// - https://github.com/hashicorp/terraform/pull/20626
+// - https://www.terraform.io/docs/configuration/types.html
 func (t *Type) Name() (string, error) {
-	goString := t.GoString()
-	// drop `cty.` prefix for simplicity. (e.g. cty.String => String)
-	name := strings.Replace(goString, "cty.", "", -1)
+	switch {
+	case t.IsPrimitiveType():
+		switch t.Type {
+		case cty.String:
+			return "string", nil
+		case cty.Number:
+			return "number", nil
+		case cty.Bool:
+			return "bool", nil
+		}
 
-	return name, nil
+	case t.IsListType():
+		elementType := NewType(t.ElementType())
+		elementName, err := elementType.Name()
+		if err != nil {
+			return "", err
+		}
+		return "list(" + elementName + ")", nil
+
+	case t.IsSetType():
+		elementType := NewType(t.ElementType())
+		elementName, err := elementType.Name()
+		if err != nil {
+			return "", err
+		}
+		return "set(" + elementName + ")", nil
+
+	case t.IsMapType():
+		elementType := NewType(t.ElementType())
+		elementName, err := elementType.Name()
+		if err != nil {
+			return "", err
+		}
+		return "map(" + elementName + ")", nil
+
+	case t.IsTupleType():
+		elementTypes := t.TupleElementTypes()
+		elementNames := make([]string, 0, len(elementTypes))
+		for i := range elementTypes {
+			elementType := NewType(t.TupleElementType(i))
+			elementName, err := elementType.Name()
+			if err != nil {
+				return "", err
+			}
+
+			elementNames = append(elementNames, elementName)
+		}
+		return "tuple([ " + strings.Join(elementNames, ", ") + " ])", nil
+	case t.IsObjectType():
+		attributeTypes := t.AttributeTypes()
+		attributeNames := make([]string, 0, len(attributeTypes))
+		for k := range attributeTypes {
+			attributeNames = append(attributeNames, k)
+		}
+		sort.Strings(attributeNames)
+
+		attributes := make([]string, 0, len(attributeTypes))
+		for _, k := range attributeNames {
+			elementType := NewType(t.AttributeType(k))
+			elementName, err := elementType.Name()
+			if err != nil {
+				return "", err
+			}
+
+			attributes = append(attributes, k+"="+elementName)
+		}
+		return "object({ " + strings.Join(attributes, ", ") + " })", nil
+
+	case t.IsCapsuleType():
+		// We notice that there is a capsule type as a cty specification,
+		// but we don't know how to handle it properly,
+		// so we should make an error for now..
+		return "", fmt.Errorf("Failed to get name for unsupported capsule type: %#v", t)
+
+	default:
+		// should never happen
+		return "", fmt.Errorf("Failed to get name for unknown type: %#v", t)
+	}
+
+	// should never happen
+	return "", fmt.Errorf("Failed to get name for type: %#v", t)
 }