Add pacman (alpm) parser support (#943)

Co-authored-by: Christopher Phillips <christopher.phillips@anchore.com>

internal/formats/syftjson/model/linux_release.go

@@ -13,6 +13,10 @@ type LinuxRelease struct {
 	IDLike           IDLikes `json:"idLike,omitempty"`
 	Version          string  `json:"version,omitempty"`
 	VersionID        string  `json:"versionID,omitempty"`
+	VersionCodename  string  `json:"versionCodename,omitempty"`
+	BuildID          string  `json:"buildID,omitempty"`
+	ImageID          string  `json:"imageID,omitempty"`
+	ImageVersion     string  `json:"imageVersion,omitempty"`
 	Variant          string  `json:"variant,omitempty"`
 	VariantID        string  `json:"variantID,omitempty"`
 	HomeURL          string  `json:"homeURL,omitempty"`

internal/formats/syftjson/model/package.go

@@ -47,7 +47,6 @@ func (p *packageMetadataUnpacker) String() string {
 }
 
 // UnmarshalJSON is a custom unmarshaller for handling basic values and values with ambiguous types.
-// nolint:funlen
 func (p *Package) UnmarshalJSON(b []byte) error {
 	var basic PackageBasicData
 	if err := json.Unmarshal(b, &basic); err != nil {
@@ -61,9 +60,19 @@ func (p *Package) UnmarshalJSON(b []byte) error {
 		return err
 	}
 
-	p.MetadataType = unpacker.MetadataType
+	return unpackMetadata(p, unpacker)
+}
 
+// nolint:funlen
+func unpackMetadata(p *Package, unpacker packageMetadataUnpacker) error {
+	p.MetadataType = unpacker.MetadataType
 	switch p.MetadataType {
+	case pkg.AlpmMetadataType:
+		var payload pkg.AlpmMetadata
+		if err := json.Unmarshal(unpacker.Metadata, &payload); err != nil {
+			return err
+		}
+		p.Metadata = payload
 	case pkg.ApkMetadataType:
 		var payload pkg.ApkMetadata
 		if err := json.Unmarshal(unpacker.Metadata, &payload); err != nil {