fix and simplify cycle detection

store.js

@@ -50,29 +50,29 @@ assign(Store.prototype, {
 		var computed = this._computed;
 		var sorted = this._sortedComputedProperties = [];
 		var visited = blankObject();
-		var cycles = blankObject();
+		var currentKey;
 
 		function visit(key) {
-			if (visited[key]) return;
-			visited[key] = true;
-
 			var c = computed[key];
 
 			if (c) {
-				if (!cycles[key]) cycles[key] = blankObject();
 				c.deps.forEach(dep => {
-					if (cycles[dep] && cycles[dep][key]) {
+					if (dep === currentKey) {
 						throw new Error(`Cyclical dependency detected between ${dep} <-> ${key}`);
 					}
-					cycles[key][dep] = true;
+
 					visit(dep);
 				});
+
+				if (!visited[key]) {
+					visited[key] = true;
 					sorted.push(c);
 				}
 			}
+		}
 
 		for (var key in this._computed) {
-			visit(key);
+			visit(currentKey = key);
 		}
 	},
 

test/store/index.js

@@ -141,8 +141,9 @@ describe('store', () => {
 
 			assert.throws(() => {
 				store.compute('a', ['b'], b => b + 1);
-				store.compute('b', ['a'], a => a + 1);
+				store.compute('b', ['c'], c => c + 1);
-			}, /Cyclical dependency detected/);
+				store.compute('c', ['a'], a => a + 1);
+			}, /Cyclical dependency detected between a <-> c/);
 		});
 
 		it('does not falsely report cycles', () => {