[ENHANCEMENT] use EMBER_NODE_PATH to specify node_modules path

ember-cli will use the value in env.EMBER_NODE_PATH if it is provided
to look up addons when `require`-ing them. This allows a user to
have their `node_modules` path outside of the project root.

Previously, the ember-cli custom require code assumed that
`node_modules` is always in the project's root.

lib/cli/node-modules-path.js

@@ -0,0 +1,51 @@
+'use strict';
+
+var path  = require('path');
+
+function isSubdirectoryOf(parentPath, possibleChildPath) {
+  return possibleChildPath.length > parentPath.length &&
+    possibleChildPath.indexOf(parentPath) === 0;
+}
+
+// A utility function for determining what path an addon may be found at. Addons
+// will only be resolved in the project's local `node_modules/` directory. This
+// is in contrast to a plain `require('some-module')` lookup, which would resolve
+// a library according to the paths in NODE_PATH.
+//
+// A description of node's lookup logic can be found here:
+//
+// * https://nodejs.org/api/modules.html#modules_all_together
+//
+// By requiring with an absolute path this logic is bypassed.
+//
+module.exports = function nodeModulesPath(context) {
+
+  // Optionally configure a different home for `node_modules/` in a parent
+  // directory of the project. Possible use cases for this include caching
+  // the `node_modules/` directory outside of a source code checkout, and
+  // ensuring the same source code (shared over a network) can be used with
+  // different environments (Linux, OSX) where binary compatibility may not
+  // exist.
+  //
+  // For example, you can specify a different home directory for modules:
+  //
+  //   EMBER_NODE_PATH=/opt/deps/node_modules NODE_PATH=/opt/deps/node_modules ember build
+  //
+  var nodePath = process.env.EMBER_NODE_PATH;
+  var contextPath = path.resolve(context);
+
+  if (nodePath) {
+    var configuredPath = path.resolve(nodePath);
+
+    // The contextPath is likely the project root, or possibly a subdirectory in
+    // node_modules/ nested dependencies. If it is more specific (a subdirectory
+    // of) than the configuredPath prefer the more specific contextPath.
+    if (isSubdirectoryOf(configuredPath, contextPath)) {
+      return path.resolve(contextPath,'node_modules');
+    } else {
+      return path.resolve(nodePath);
+    }
+  } else {
+    return path.resolve(contextPath,'node_modules');
+  }
+};

lib/models/addon-discovery.js

@@ -4,13 +4,14 @@
 @module ember-cli
 */
 
-var assign     = require('lodash/object/assign');
-var debug      = require('debug')('ember-cli:addon-discovery');
-var fs         = require('fs');
-var path       = require('path');
-var CoreObject = require('core-object');
-var resolve    = require('resolve');
-var findup     = require('findup');
+var assign          = require('lodash/object/assign');
+var debug           = require('debug')('ember-cli:addon-discovery');
+var fs              = require('fs');
+var path            = require('path');
+var CoreObject      = require('core-object');
+var resolve         = require('resolve');
+var findup          = require('findup');
+var nodeModulesPath = require ('../cli/node-modules-path');
 
 /**
   AddonDiscovery is responsible for collecting information about all of the
@@ -103,7 +104,7 @@ AddonDiscovery.prototype.discoverFromDependencies = function(root, pkg, excludeD
 
       // this supports packages that do not have a valid entry point
       // script (aka `main` entry in `package.json` or `index.js`)
-      addonPath = path.join(root, 'node_modules', name);
+      addonPath = path.join(nodeModulesPath(root), name);
       var addon = discovery.discoverAtPath(addonPath);
       if (addon) {
         var chalk = require('chalk');

lib/models/project.js

@@ -3,23 +3,24 @@
 /**
 @module ember-cli
 */
-var Promise         = require('../ext/promise');
-var path            = require('path');
-var findup          = Promise.denodeify(require('findup'));
-var resolve         = Promise.denodeify(require('resolve'));
-var fs              = require('fs');
-var find            = require('lodash/collection/find');
-var assign          = require('lodash/object/assign');
-var forOwn          = require('lodash/object/forOwn');
-var merge           = require('lodash/object/merge');
-var debug           = require('debug')('ember-cli:project');
-var AddonDiscovery  = require('../models/addon-discovery');
-var AddonsFactory   = require('../models/addons-factory');
-var Command         = require('../models/command');
-var UI              = require('../ui');
-
-var versionUtils    = require('../utilities/version-utils');
-var emberCLIVersion = versionUtils.emberCLIVersion;
+var Promise          = require('../ext/promise');
+var path             = require('path');
+var findup           = Promise.denodeify(require('findup'));
+var resolve          = Promise.denodeify(require('resolve'));
+var fs               = require('fs');
+var find             = require('lodash/collection/find');
+var assign           = require('lodash/object/assign');
+var forOwn           = require('lodash/object/forOwn');
+var merge            = require('lodash/object/merge');
+var debug            = require('debug')('ember-cli:project');
+var AddonDiscovery   = require('../models/addon-discovery');
+var AddonsFactory    = require('../models/addons-factory');
+var Command          = require('../models/command');
+var UI               = require('../ui');
+var nodeModulesPath  = require('../cli/node-modules-path');
+
+var versionUtils     = require('../utilities/version-utils');
+var emberCLIVersion  = versionUtils.emberCLIVersion;
 
 /**
   The Project model is tied to your package.json. It is instiantiated
@@ -216,7 +217,7 @@ Project.prototype.require = function(file) {
   if (/^\.\//.test(file)) { // Starts with ./
     return require(path.join(this.root, file));
   } else {
-    return require(path.join(this.root, 'node_modules', file));
+    return require(path.join(nodeModulesPath(this.root), file));
   }
 };
 

lib/utilities/require-local.js

@@ -1,7 +1,8 @@
 'use strict';
 
-var path = require('path');
+var path            = require('path');
+var nodeModulesPath = require('../cli/node-modules-path');
 
 module.exports = function requireLocal(lib) {
-  return require(path.join(process.cwd(), 'node_modules', lib));
+  return require(path.join(nodeModulesPath(process.cwd()), lib));
 };

tests/unit/cli/node-modules-path-test.js

@@ -0,0 +1,43 @@
+'use strict';
+/*jshint expr: true*/
+
+var expect  = require('chai').expect;
+var path    = require('path');
+var nodeModulesPath = require('../../../lib/cli/node-modules-path');
+
+describe('cli/node-module-path.js', function() {
+
+  afterEach(function() {
+    delete process.env.EMBER_NODE_PATH;
+  });
+
+
+  it('nodeModulesPath() should return the local node_modules path by default.', function() {
+    // Valid commands
+    var expectedPath = path.join(process.cwd(),'node_modules');
+
+    expect(
+      nodeModulesPath(process.cwd())
+    ).to.equal(expectedPath);
+  });
+
+  it('nodeModulesPath() should return subdirectories of EMBER_NODE_PATH when set to an absolute path.', function() {
+    if (process.platform === 'win32') {
+      process.env.EMBER_NODE_PATH = 'C:\\tmp\node_modules';
+    } else {
+      process.env.EMBER_NODE_PATH = '/tmp/node_modules';
+    }
+
+    expect(nodeModulesPath(process.cwd())).to.equal(path.resolve(process.env.EMBER_NODE_PATH));
+
+    var addOnPath = path.resolve(process.env.EMBER_NODE_PATH, 'node_modules', 'my-add-on');
+    var addOnModulesPath = path.resolve(process.env.EMBER_NODE_PATH, 'node_modules', 'my-add-on', 'node_modules');
+    expect(nodeModulesPath(addOnPath)).to.equal(addOnModulesPath);
+  });
+
+  it('nodeModulesPath() should return subdirectories of EMBER_NODE_PATH when set to a relative path.', function() {
+    process.env.EMBER_NODE_PATH = '../../tmp/node_modules';
+    expect(nodeModulesPath(process.cwd())).to.equal(path.resolve('../../tmp','node_modules'));
+    expect(nodeModulesPath('../../tmp/node_modules/my-add-on')).to.equal(path.resolve('../../tmp','node_modules','my-add-on','node_modules'));
+  });
+});