Support type aliases when type-hashing

src/type-hash.js

@@ -116,6 +116,12 @@ function hashType(type, level = 0, seenTypes = new Map()) {
 					typeHash: hashType(actualTrait, level + 1, seenTypes)
 				};
 			}
+		} else if (rule._isTypeAlias === true) {
+			/* Should we wrap this in an `alias` to represent alias-level additional constraints? Or should we just return the canonical rule for the _alias itself? */
+			props = {
+				ruleType: "alias",
+				type: rule._alias
+			};
 		} else {
 			throw new Error(`Unrecognized rule type: ${util.inspect(rule)}`);
 		}