small adjustments to string prefix

Author: austinvalle

tftypes/refinement/nullness.go

@@ -2,34 +2,38 @@ package refinement
 
 import "github.com/vmihailenco/msgpack/v5"
 
-type nullness struct {
-	Value bool
+type Nullness struct {
+	value bool
 }
 
-func (n nullness) Encode(enc *msgpack.Encoder) error {
+func (n Nullness) Encode(enc *msgpack.Encoder) error {
 	err := enc.EncodeInt(int64(KeyNullness))
 	if err != nil {
 		return err
 	}
 
-	// A value that is definitely null cannot be unknown
-	return enc.EncodeBool(false)
+	// It shouldn't be possible for an unknown value to be definitely null (i.e. nullness.value = true),
+	// as that should be represented by a known null value instead. This encoding is in place to be compliant
+	// with Terraform's encoding which uses a definitely null refinement to collapse into a known null value.
+	return enc.EncodeBool(n.value)
 }
 
-func (n nullness) Equal(Refinement) bool {
+func (n Nullness) Equal(Refinement) bool {
 	return false
 }
 
-func (n nullness) String() string {
-	return "todo - nullness"
+func (n Nullness) String() string {
+	return "todo - Nullness"
 }
 
-func (n nullness) unimplementable() {}
+func (n Nullness) NotNull() bool {
+	return !n.value
+}
+
+func (n Nullness) unimplementable() {}
 
-// TODO: Should this accept a value? If a value is unknown and the it's refined to be null
-// then the value should be a known value of null instead.
-func Nullness(value bool) Refinement {
-	return nullness{
-		Value: value,
+func NewNullness(value bool) Refinement {
+	return Nullness{
+		value: value,
 	}
 }

tftypes/refinement/string_prefix.go

@@ -2,21 +2,21 @@ package refinement
 
 import "github.com/vmihailenco/msgpack/v5"
 
-type stringPrefix struct {
-	Value string
+type StringPrefix struct {
+	value string
 }
 
 // TODO: What if the prefix is empty? Should we skip encoding? Throw an error earlier? Throw an error here?
 // - I think an empty prefix string is valid, empty string is still more information then wholly unknown?
 // - I wonder what Terraform does in this situation today
-func (s stringPrefix) Encode(enc *msgpack.Encoder) error {
+func (s StringPrefix) Encode(enc *msgpack.Encoder) error {
 	// Matching go-cty for the max prefix length allowed here
 	//
 	// This ensures the total size of the refinements blob does not exceed the limit
 	// set by the decoder (1024).
 	maxPrefixLength := 256
-	prefix := s.Value
-	if len(s.Value) > maxPrefixLength {
+	prefix := s.value
+	if len(s.value) > maxPrefixLength {
 		prefix = prefix[:maxPrefixLength-1]
 	}
 
@@ -28,18 +28,22 @@ func (s stringPrefix) Encode(enc *msgpack.Encoder) error {
 	return enc.EncodeString(prefix)
 }
 
-func (s stringPrefix) Equal(Refinement) bool {
+func (s StringPrefix) Equal(Refinement) bool {
 	return false
 }
 
-func (s stringPrefix) String() string {
+func (s StringPrefix) String() string {
 	return "todo - stringPrefix"
 }
 
-func (s stringPrefix) unimplementable() {}
+func (s StringPrefix) PrefixValue() string {
+	return s.value
+}
+
+func (s StringPrefix) unimplementable() {}
 
-func StringPrefix(value string) Refinement {
-	return stringPrefix{
-		Value: value,
+func NewStringPrefix(value string) Refinement {
+	return StringPrefix{
+		value: value,
 	}
 }

tftypes/value_msgpack.go

@@ -421,7 +421,11 @@ func msgpackUnmarshalUnknown(dec *msgpack.Decoder, typ Type, path *AttributePath
 			// The presence of this key means we're refining the null-ness one
 			// way or another. If nullness is unknown then this key should not
 			// be present at all.
-			newRefinements[keyCode] = refinement.Nullness(isNull)
+			//
+			// isNull should always be false if this refinement is present, but to match Terraform's support
+			// of this encoding, we will pass along the value. If isNull is true, then the value should not be
+			// unknown with refinements, it should be a known null value.
+			newRefinements[keyCode] = refinement.NewNullness(isNull)
 		case refinement.KeyStringPrefix:
 			if !typ.Is(String) {
 				return Value{}, path.NewErrorf("failed to decode msgpack extension body: string prefix refinement for non-string type")
@@ -436,7 +440,7 @@ func msgpackUnmarshalUnknown(dec *msgpack.Decoder, typ Type, path *AttributePath
 
 			// TODO: If terraform doesn't support an empty string prefix, then neither should we, potentially return an error here.
 
-			newRefinements[keyCode] = refinement.StringPrefix(prefix)
+			newRefinements[keyCode] = refinement.NewStringPrefix(prefix)
 		default:
 			// We don't want to error here, as go-cty could introduce new refinements that we'd
 			// want to just ignore until this logic is updated