database: Add parent feature pointer to Feature struct

Feature now has a pointer to parent feature. If a vulnerability affects
a parent feature, this child feature will be affected.

database/models.go

@@ -165,6 +165,12 @@ type Feature struct {
 	Name          string
 	Version       string
 	VersionFormat string
+
+	// Parent feature indicates that the vulnerability affects parent feature
+	// will also affect this feature.
+	//
+	// e.g. A source package is the parent feature of a binary package.
+	Parent *Feature
 }
 
 // NamespacedFeature is a feature with determined namespace and can be affected

database/pgsql/testutil.go

@@ -26,10 +26,10 @@ import (
 // int keys must be the consistent with the database ID.
 var (
 	realFeatures = map[int]database.Feature{
-		1: {"ourchat", "0.5", "dpkg"},
+		1: {"ourchat", "0.5", "dpkg", nil},
-		2: {"openssl", "1.0", "dpkg"},
+		2: {"openssl", "1.0", "dpkg", nil},
-		3: {"openssl", "2.0", "dpkg"},
+		3: {"openssl", "2.0", "dpkg", nil},
-		4: {"fake", "2.0", "rpm"},
+		4: {"fake", "2.0", "rpm", nil},
 	}
 
 	realNamespaces = map[int]database.Namespace{