Check for cycles when traversing the dependency tree

- Cycles may occur in some cases (dependencies like
  a -> b -> c -> a)
- This commit makes #totalStats() and #totalDependencies() safe
  for cyclic.
- The method Package#collectDependencies can be used to avoid cycles
  in future aggregation methods.

src/Package.js

@@ -12,7 +12,7 @@ const debug = require('debug')('analyze-module-size:Package')
  */
 class Package {
   /**
-   * Create a new Packageobject
+   * Create a new Package object
    * @param {object} packageJson the parsed package.json file
    * @param {PackageStats} stats the statistics object
    */
@@ -49,13 +49,23 @@ class Package {
   }
 
   totalStats () {
-    return this.stats.merge(this.dependencies.map((dep) => {
-      return dep.totalStats()
-    }))
+    return this.stats.merge(Array.from(this.collectDependencies()).map((dep) => dep.stats))
   }
 
   totalDependencies () {
-    return this.dependencies.reduce((sum, dep) => sum + dep.totalDependencies() + 1, 0)
+    return this.collectDependencies().size
+  }
+
+  /**
+   * Reduce-function that not reduces the direct and recursive dependencies
+   */
+  collectDependencies (collector = new Set()) {
+    this.dependencies.forEach(function (dep) {
+      if (collector.has(dep)) return
+      collector.add(dep)
+      dep.collectDependencies(collector)
+    })
+    return collector
   }
 
   location () {

test/Package-spec.js

@@ -121,6 +121,15 @@ describe('The Package-class:', function () {
       Package.connectAll(base, [pkg1, pkg2, pkg3])
       expect(base.totalDependencies()).to.equal(2)
     })
+
+    it('should ignore cyclic dependencies', function () {
+      const base = dummy('base@1.0.0', undefined, undefined)
+      const pkg1 = dummy('one@1.0.0', '/one', ['/', '/three'])
+      const pkg2 = dummy('two@1.0.0', '/two', ['/one'])
+      const pkg3 = dummy('dev@1.0.0', '/three', ['/two'])
+      Package.connectAll(base, [pkg1, pkg2, pkg3])
+      expect(base.totalDependencies()).to.equal(3)
+    })
   })
 
   describe('The #totalStats method', function () {
@@ -145,6 +154,14 @@ describe('The Package-class:', function () {
       Package.connectAll(base, [pkg1, pkg2, pkg3])
       expect(base.totalStats()).to.deep.equal(new PackageStats('/base@1.0.0', []).merge([stats1, stats2]))
     })
+
+    it('should stop traversing at dependency cycles', function () {
+      const base = dummy('base@1.0.0', undefined, undefined)
+      const pkg1 = dummy('one@1.0.0', '/one', ['/', '/two'], stats1)
+      const pkg2 = dummy('two@1.0.0', '/two', ['/one'], stats2)
+      Package.connectAll(base, [pkg1, pkg2])
+      expect(base.totalStats()).to.deep.equal(new PackageStats('/base@1.0.0', []).merge([stats1, stats2]))
+    })
   })
 })