Implement golang Purl subpath (#2547)

* Added test for golang package that include subpath into the module

Signed-off-by: Laurent Goderre <laurent.goderre@docker.com>

* Implement golang purl subpath

Signed-off-by: Laurent Goderre <laurent.goderre@docker.com>

---------

Signed-off-by: Laurent Goderre <laurent.goderre@docker.com>

syft/pkg/cataloger/golang/package.go

@@ -1,7 +1,6 @@
 package golang
 
 import (
-	"regexp"
 	"runtime/debug"
 	"strings"
 
@@ -48,22 +47,27 @@ func packageURL(moduleName, moduleVersion string) string {
 	// source: https://github.com/package-url/purl-spec/blob/master/PURL-TYPES.rst#golang
 	// note: "The version is often empty when a commit is not specified and should be the commit in most cases when available."
 
-	re := regexp.MustCompile(`(/)[^/]*$`)
-	fields := re.Split(moduleName, -1)
+	fields := strings.Split(moduleName, "/")
 	if len(fields) == 0 {
 		return ""
 	}
-	namespace := fields[0]
-	name := strings.TrimPrefix(strings.TrimPrefix(moduleName, namespace), "/")
-
-	if name == "" {
-		// this is a "short" url (with no namespace)
-		name = namespace
-		namespace = ""
-	}
 
+	namespace := ""
+	name := ""
 	// The subpath is used to point to a subpath inside a package (e.g. pkg:golang/google.golang.org/genproto#googleapis/api/annotations)
-	subpath := "" // TODO: not implemented
+	subpath := ""
+
+	switch len(fields) {
+	case 1:
+		name = fields[0]
+	case 2:
+		name = fields[1]
+		namespace = fields[0]
+	default:
+		name = fields[2]
+		namespace = strings.Join(fields[0:2], "/")
+		subpath = strings.Join(fields[3:], "/")
+	}
 
 	return packageurl.NewPackageURL(
 		packageurl.TypeGolang,

syft/pkg/cataloger/golang/package_test.go

@@ -31,6 +31,21 @@ func Test_packageURL(t *testing.T) {
 			},
 			expected: "pkg:golang/go.opencensus.io@v0.23.0",
 		},
+		{
+			name: "golang with subpath",
+			pkg: pkg.Package{
+				Name:    "github.com/coreos/go-systemd/v22",
+				Version: "v22.1.0",
+			},
+			expected: "pkg:golang/github.com/coreos/go-systemd@v22.1.0#v22",
+		},
+		{
+			name: "golang with subpath deep",
+			pkg: pkg.Package{
+				Name: "google.golang.org/genproto/googleapis/api/annotations",
+			},
+			expected: "pkg:golang/google.golang.org/genproto/googleapis#api/annotations",
+		},
 	}
 
 	for _, test := range tests {

syft/pkg/cataloger/golang/parse_go_binary_test.go

@@ -260,7 +260,7 @@ func TestBuildGoPkgInfo(t *testing.T) {
 				{
 					Name:     "github.com/a/b/c",
 					Version:  "(devel)",
-					PURL:     "pkg:golang/github.com/a/b/c@(devel)",
+					PURL:     "pkg:golang/github.com/a/b@(devel)#c",
 					Language: pkg.Go,
 					Type:     pkg.GoModulePkg,
 					Locations: file.NewLocationSet(