Merge pull request #119 from gregory-nisbet/2025-11-01-trailing-comma

Support trailing comma after a resource.

Author: philhassey

internal/parser/cedar_unmarshal.go

@@ -112,6 +112,7 @@ func (p *Policy) fromCedar(parser *parser) error {
 	if err = parser.resource(newPolicy); err != nil {
 		return err
 	}
+	parser.skipAtMostOnce(",")
 	if err = parser.exact(")"); err != nil {
 		return err
 	}
@@ -155,6 +156,13 @@ func (p *parser) exact(tok string) error {
 	return nil
 }
 
+func (p *parser) skipAtMostOnce(tok string) {
+	t := p.peek()
+	if t.Text == tok {
+		p.advance()
+	}
+}
+
 func (p *parser) errorf(s string, args ...interface{}) error {
 	var t Token
 	if p.pos < len(p.tokens) {

internal/parser/cedar_unmarshal_test.go

@@ -590,7 +590,7 @@ func TestParsePolicySet(t *testing.T) {
 		policyStr := []byte(`permit (
 			principal,
 			action,
-			resource
+			resource,
 		);`)
 
 		var policies parser.PolicySlice

policy_test.go

@@ -71,7 +71,7 @@ func TestPolicyCedar(t *testing.T) {
 	t.Parallel()
 
 	// Taken from https://docs.cedarpolicy.com/policies/syntax-policy.html
-	policyStr := `permit (
+	const policyStr = `permit (
     principal,
     action == Action::"editPhoto",
     resource
@@ -84,6 +84,29 @@ when { resource.owner == principal };`
 	testutil.Equals(t, string(policy.MarshalCedar()), policyStr)
 }
 
+func TestPolicyCedar_TrailingComma(t *testing.T) {
+	t.Parallel()
+
+	const policyStr = `permit (
+    principal,
+    action == Action::"editPhoto",
+    resource
+)
+when { resource.owner == principal };`
+
+	const policyStrTrailingComma = `permit (
+    principal,
+    action == Action::"editPhoto",
+    resource,
+)
+when { resource.owner == principal };`
+
+	var policy cedar.Policy
+	testutil.OK(t, policy.UnmarshalCedar([]byte(policyStrTrailingComma)))
+
+	testutil.Equals(t, string(policy.MarshalCedar()), policyStr)
+}
+
 func TestPolicyAST(t *testing.T) {
 	t.Parallel()