Fix a json-to-human schema translation bug (#693)

Signed-off-by: Shaobo He <[email protected]>

cedar-policy-validator/src/human_schema/fmt.rs

@@ -153,6 +153,12 @@ impl Display for ActionType {
                     write!(f, "\n}}")?;
                 }
             }
+        } else {
+            // No `appliesTo` key: both principal and resource must be unspecified entities
+            write!(f, "appliesTo {{")?;
+            // context is an empty record
+            write!(f, "  context: {{}}")?;
+            write!(f, "\n}}")?;
         }
         Ok(())
     }

cedar-policy-validator/src/human_schema/test.rs

@@ -309,7 +309,8 @@ mod demo_tests {
         let namespace = NamespaceDefinition::new(empty(), once(("foo".to_smolstr(), action)));
         let fragment = SchemaFragment(HashMap::from([("bar".to_smolstr(), namespace)]));
         let as_src = fragment.as_natural_schema().unwrap();
-        let expected = r#"action "foo" ;"#;
+        let expected = r#"action "foo" appliesTo {  context: {}
+};"#;
         assert!(as_src.contains(expected), "src was:\n`{as_src}`");
     }