Allow config authors to always use Prefix

Previously an unset Location was only allowed for wildcarded Prefixes.
This commit will allow any valid Prefix.

Fixes: containers#1191 (comment)

Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org>

pkg/sysregistriesv2/system_registries_v2.go

@@ -357,21 +357,26 @@ func (config *V2RegistriesConf) postProcessRegistries() error {
 			return err
 		}
 
-		if reg.Prefix == "" {
-			if reg.Location == "" {
-				return &InvalidRegistries{s: "invalid condition: both location and prefix are unset"}
-			}
-			reg.Prefix = reg.Location
-		} else {
+		// Allow config authors to always use Prefix.
+		if reg.Prefix != "" {
 			reg.Prefix, err = parseLocation(reg.Prefix)
 			if err != nil {
 				return err
 			}
-			// FIXME: allow config authors to always use Prefix.
-			// https://github.com/containers/image/pull/1191#discussion_r610622495
-			if reg.Prefix[:2] != "*." && reg.Location == "" {
-				return &InvalidRegistries{s: "invalid condition: location is unset and prefix is not in the format: *.example.com"}
+			if reg.Location != "" {
+				reg.Location, err = parseLocation(reg.Location)
+				if err != nil {
+					return err
+				}
+			}
+		} else if reg.Location != "" {
+			reg.Prefix, err = parseLocation(reg.Location)
+			if err != nil {
+				return err
 			}
+			reg.Location = reg.Prefix
+		} else {
+			return &InvalidRegistries{s: "invalid condition: both location and prefix are unset"}
 		}
 
 		// make sure mirrors are valid