Implement review feedback: omit empty fields and proper error wrapping

- Use %w for proper error wrapping as suggested by @anderseknert
- Omit empty optional fields as suggested by @srenatus
- Update tests to match new behavior
- This makes the API more idiomatic to Rego where checking for field
  existence is clearer than checking for empty strings

Signed-off-by: Anivar A Aravind <[email protected]>

Author: Anivar A Aravind

v1/topdown/purl.go

@@ -31,25 +31,35 @@ func builtinPurlParse(_ BuiltinContext, operands []*ast.Term, iter func(*ast.Ter
 
 	purl, err := packageurl.FromString(string(str))
 	if err != nil {
-		return fmt.Errorf("invalid PURL %q: %s", str, err)
+		return fmt.Errorf("invalid PURL %q: %w", str, err)
 	}
 
-	// Handle qualifiers - always return an object (empty if no qualifiers)
-	qualifiers := ast.NewObject()
-	for _, q := range purl.Qualifiers {
-		qualifiers.Insert(ast.StringTerm(q.Key), ast.StringTerm(q.Value))
-	}
-
-	// Create object with all PURL components in a single operation
+	// Create object with required fields
 	obj := ast.NewObject(
 		[2]*ast.Term{ast.InternedTerm("type"), ast.StringTerm(purl.Type)},
 		[2]*ast.Term{ast.InternedTerm("name"), ast.StringTerm(purl.Name)},
-		[2]*ast.Term{ast.InternedTerm("namespace"), ast.StringTerm(purl.Namespace)},
-		[2]*ast.Term{ast.InternedTerm("version"), ast.StringTerm(purl.Version)},
-		[2]*ast.Term{ast.InternedTerm("subpath"), ast.StringTerm(purl.Subpath)},
-		[2]*ast.Term{ast.InternedTerm("qualifiers"), ast.NewTerm(qualifiers)},
 	)
 
+	// Add optional fields only if present
+	if purl.Namespace != "" {
+		obj.Insert(ast.InternedTerm("namespace"), ast.StringTerm(purl.Namespace))
+	}
+	if purl.Version != "" {
+		obj.Insert(ast.InternedTerm("version"), ast.StringTerm(purl.Version))
+	}
+	if purl.Subpath != "" {
+		obj.Insert(ast.InternedTerm("subpath"), ast.StringTerm(purl.Subpath))
+	}
+	
+	// Add qualifiers only if present
+	if len(purl.Qualifiers) > 0 {
+		qualifiers := ast.NewObject()
+		for _, q := range purl.Qualifiers {
+			qualifiers.Insert(ast.StringTerm(q.Key), ast.StringTerm(q.Value))
+		}
+		obj.Insert(ast.InternedTerm("qualifiers"), ast.NewTerm(qualifiers))
+	}
+
 	return iter(ast.NewTerm(obj))
 }
 

v1/topdown/purl_test.go

@@ -84,23 +84,18 @@ func TestBuiltinPurlParse(t *testing.T) {
 		{
 			input: `"pkg:npm/[email protected]"`,
 			expected: map[string]interface{}{
-				"type":       "npm",
-				"namespace":  "",
-				"name":       "foobar",
-				"version":    "12.3.1",
-				"qualifiers": map[string]interface{}{},
-				"subpath":    "",
+				"type":    "npm",
+				"name":    "foobar",
+				"version": "12.3.1",
 			},
 		},
 		{
 			input: `"pkg:maven/org.apache.xmlgraphics/[email protected]"`,
 			expected: map[string]interface{}{
-				"type":       "maven",
-				"namespace":  "org.apache.xmlgraphics",
-				"name":       "batik-anim",
-				"version":    "1.9.1",
-				"qualifiers": map[string]interface{}{},
-				"subpath":    "",
+				"type":      "maven",
+				"namespace": "org.apache.xmlgraphics",
+				"name":      "batik-anim",
+				"version":   "1.9.1",
 			},
 		},
 		{
@@ -114,18 +109,16 @@ func TestBuiltinPurlParse(t *testing.T) {
 					"arch":   "i386",
 					"distro": "fedora-25",
 				},
-				"subpath": "",
 			},
 		},
 		{
 			input: `"pkg:deb/debian/[email protected]#src/curl.c"`,
 			expected: map[string]interface{}{
-				"type":       "deb",
-				"namespace":  "debian",
-				"name":       "curl",
-				"version":    "7.50.3-1",
-				"qualifiers": map[string]interface{}{},
-				"subpath":    "src/curl.c",
+				"type":      "deb",
+				"namespace": "debian",
+				"name":      "curl",
+				"version":   "7.50.3-1",
+				"subpath":   "src/curl.c",
 			},
 		},
 	}