find-cycles (aws#350)

Add a tool by @rix0rrr to help find cycles.
Add instructions in CONTRIBUTING

CONTRIBUTING.md

@@ -206,6 +206,22 @@ Guidelines:
    `^1.2.3`). This enables non-breaking updates to automatically be picked up.
  * Make sure `package-lock.json` files are included in your commit.
 
+### Finding Dependency Cycles
+
+You can use `find-cycles` to print a list of internal dependency cycles:
+
+```shell
+$ tools/find-cycles/find-cycles.sh
+Cycle: @aws-cdk/iam => @aws-cdk/assert => aws-cdk => @aws-cdk/s3 => @aws-cdk/kms => @aws-cdk/iam
+Cycle: @aws-cdk/assert => aws-cdk => @aws-cdk/s3 => @aws-cdk/kms => @aws-cdk/assert
+Cycle: @aws-cdk/iam => @aws-cdk/assert => aws-cdk => @aws-cdk/s3 => @aws-cdk/iam
+Cycle: @aws-cdk/assert => aws-cdk => @aws-cdk/s3 => @aws-cdk/assert
+Cycle: @aws-cdk/assert => aws-cdk => @aws-cdk/cloudformation => @aws-cdk/assert
+Cycle: @aws-cdk/iam => @aws-cdk/assert => aws-cdk => @aws-cdk/util => @aws-cdk/iam
+Cycle: @aws-cdk/sns => @aws-cdk/lambda => @aws-cdk/codecommit => @aws-cdk/sns
+Cycle: @aws-cdk/sns => @aws-cdk/lambda => @aws-cdk/codecommit => @aws-cdk/codepipeline => @aws-cdk/sns
+```
+
 ### Updating all Dependencies
 
 We use `npm update` to
@@ -223,4 +239,4 @@ We use `npm update` to
 5. Now, run `./build.sh` again to verify all tests pass.
 6. Submit a Pull Request.
 
-[CHANGELOG]: [./CHANGELOG.md]
+[CHANGELOG]: [./CHANGELOG.md]

tools/find-cycles/find-cycles.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+import json
+import sys
+import collections
+import pprint
+
+def find(xs, x):
+  for i, value in enumerate(xs):
+    if x == value:
+      return i
+  return None
+
+filenames = sys.argv[1:]
+
+graph = collections.defaultdict(set)
+for filename in filenames:
+  with file(filename) as f:
+    package_json = json.load(f)
+
+  for key in ['devDependencies', 'dependencies']:
+    if key in package_json:
+      graph[package_json['name']].update(package_json[key].keys())
+
+
+checked = set()
+
+# Do a check for cycles for each package. This is slow but it works,
+# and it has the advantage that it can give good diagnostics.
+def check_for_cycles(package, path):
+  i = find(path, package)
+  if i is not None:
+    cycle = path[i:] + [package]
+    print 'Cycle: %s' % ' => '.join(cycle)
+    return
+
+  if package in checked:
+    return
+
+  checked.add(package)
+
+  deps = graph.get(package, [])
+  for dep in deps:
+    check_for_cycles(dep, path + [package])
+
+for package in graph.keys():
+  check_for_cycles(package, [])

tools/find-cycles/find-cycles.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+set -euo pipefail
+scriptdir="$(cd $(dirname $0) && pwd)"
+python ${scriptdir}/find-cycles.py  $(find . -name package.json | grep -v node_modules)