fix: Standarize/disambiguate return from Parse

Author: nima

digest.go

@@ -80,7 +80,10 @@ var (
 // be returned if the format is invalid.
 func Parse(s string) (Digest, error) {
 	d := Digest(s)
-	return d, d.Validate()
+	if err := d.Validate(); err != nil {
+		return "", err
+	}
+	return d, nil
 }
 
 // FromReader consumes the content of rd until io.EOF, returning canonical digest.
@@ -137,7 +140,7 @@ func (d Digest) Encoded() string {
 	return string(d[d.sepIndex()+1:])
 }
 
-// Hex is deprecated. Please use Digest.Encoded.
+// Deprecated: Hex has been deprecated in favor of Digest.Encoded
 func (d Digest) Hex() string {
 	return d.Encoded()
 }

digestset/set.go

@@ -91,15 +91,17 @@ func (dst *Set) Lookup(d string) (digest.Digest, error) {
 		searchFunc func(int) bool
 		alg        digest.Algorithm
 		hex        string
+		dgst       digest.Digest
 	)
-	dgst, err := digest.Parse(d)
-	if err == digest.ErrDigestInvalidFormat {
+
+	dgst = digest.Digest(d)
+	if err := dgst.Validate(); err == digest.ErrDigestInvalidFormat {
 		hex = d
 		searchFunc = func(i int) bool {
 			return dst.entries[i].val >= d
 		}
-	} else {
-		hex = dgst.Hex()
+	} else { // Note: `err` is not necessarily `nil` here
+		hex = dgst.Encoded()
 		alg = dgst.Algorithm()
 		searchFunc = func(i int) bool {
 			if dst.entries[i].val == hex {