test: test cases for circular symlinked deps and peer deps

Adds a test case in the known-test cases to catch nodejs#5950
Adds a test to verify that circular symlinked deps do not recurse
forever.

test/known_issues/test-symlinked-peer-modules.js

@@ -0,0 +1,77 @@
+/* eslint no-irregular-whitespace: 0 */
+'use strict';
+// Refs: https://github.com/nodejs/node/pull/5950
+
+// This test illustrates the problem that symlinked modules are unable
+// to find their peer dependencies. This was fixed in #5950 but that is
+// reverted because that particular way of fixing it causes too much
+// breakage (breakage that was not caught by either CI or CITGM on multiple
+// runs.
+
+// This test passes in v6 with https://github.com/nodejs/node/pull/5950 but
+// fails with https://github.com/nodejs/node/pull/5950 reverted. This test
+// will fail in Node.js v4 and v5.
+
+const common = require('../common');
+const fs = require('fs');
+const path = require('path');
+const assert = require('assert');
+
+common.refreshTmpDir();
+
+const tmpDir = common.tmpDir;
+
+// Creates the following structure
+// {tmpDir}
+// ├── app
+// │   ├── index.js
+// │   └── node_modules
+// │       ├── moduleA -> {tmpDir}/moduleA
+// │       └── moduleB
+// │           ├── index.js
+// │           └── package.json
+// └── moduleA
+//     ├── index.js
+//     └── package.json
+
+const moduleA = path.join(tmpDir, 'moduleA');
+const app = path.join(tmpDir, 'app');
+const moduleB = path.join(app, 'node_modules', 'moduleB');
+const moduleA_link = path.join(app, 'node_modules', 'moduleA');
+fs.mkdirSync(moduleA);
+fs.mkdirSync(app);
+fs.mkdirSync(path.join(app, 'node_modules'));
+fs.mkdirSync(moduleB);
+
+// Attempt to make the symlink. If this fails due to lack of sufficient
+// permissions, the test will bail out and be skipped.
+try {
+  fs.symlinkSync(moduleA, moduleA_link);
+} catch (err) {
+  if (err.code !== 'EPERM') throw err;
+  console.log('1..0 # Skipped: insufficient privileges for symlinks');
+  return;
+}
+
+fs.writeFileSync(path.join(moduleA, 'package.json'),
+                 JSON.stringify({name: 'moduleA', main: 'index.js'}), 'utf8');
+fs.writeFileSync(path.join(moduleA, 'index.js'),
+                 'module.exports = require(\'moduleB\');', 'utf8');
+fs.writeFileSync(path.join(app, 'index.js'),
+                 '\'use strict\'; require(\'moduleA\');', 'utf8');
+fs.writeFileSync(path.join(moduleB, 'package.json'),
+                 JSON.stringify({name: 'moduleB', main: 'index.js'}), 'utf8');
+fs.writeFileSync(path.join(moduleB, 'index.js'),
+                 'module.exports = 1;', 'utf8');
+
+// TODO(@jasnell): Update this comment with this issue is fixed and
+// this test is moved out of the known_issues directory.
+//
+// Ideally, this should not throw but it does because moduleA is not
+// able to find it's peer dependency moduleB. The reason it cannot find
+// it's peer is because moduleA is cached at it's realpath and when it's
+// require goes to find moduleA, it can't (because moduleB does not exist
+// within it's lookup path).
+assert.doesNotThrow(() => {
+  require(path.join(app, 'index'));
+});

test/sequential/test-module-circular-symlinks.js

@@ -0,0 +1,69 @@
+/* eslint no-irregular-whitespace: 0 */
+'use strict';
+
+// This tests to make sure that modules with symlinked circular dependencies
+// do not blow out the module cache and recurse forever. See issue
+// https://github.com/nodejs/node/pull/5950 for context. PR #5950 attempted
+// to solve a problem with symlinked peer dependencies by caching using the
+// symlink path. Unfortunately, that breaks the case tested in this module
+// because each symlinked module, despite pointing to the same code on disk,
+// is loaded and cached as a separate module instance, which blows up the
+// cache and leads to a recursion bug.
+
+// This test should pass in Node.js v4 and v5. It should pass in Node.js v6
+// after https://github.com/nodejs/node/pull/5950 has been reverted.
+
+const common = require('../common');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs');
+
+// {tmpDir}
+// ├── index.js
+// └── node_modules
+//     ├── moduleA
+//     │   ├── index.js
+//     │   └── node_modules
+//     │       └── moduleB -> {tmpDir}/node_modules/moduleB
+//     └── moduleB
+//         ├── index.js
+//         └── node_modules
+//             └── moduleA -> {tmpDir}/node_modules/moduleA
+
+common.refreshTmpDir();
+const tmpDir = common.tmpDir;
+
+const node_modules = path.join(tmpDir, 'node_modules');
+const moduleA = path.join(node_modules, 'moduleA');
+const moduleB = path.join(node_modules, 'moduleB');
+const moduleA_link = path.join(moduleB, 'node_modules', 'moduleA');
+const moduleB_link = path.join(moduleA, 'node_modules', 'moduleB');
+
+fs.mkdirSync(node_modules);
+fs.mkdirSync(moduleA);
+fs.mkdirSync(moduleB);
+fs.mkdirSync(path.join(moduleA, 'node_modules'));
+fs.mkdirSync(path.join(moduleB, 'node_modules'));
+
+try {
+  fs.symlinkSync(moduleA, moduleA_link);
+  fs.symlinkSync(moduleB, moduleB_link);
+} catch (err) {
+  if (err.code !== 'EPERM') throw err;
+  console.log('1..0 # Skipped: insufficient privileges for symlinks');
+  return;
+}
+
+fs.writeFileSync(path.join(tmpDir, 'index.js'),
+                 'module.exports = require(\'moduleA\');', 'utf8');
+fs.writeFileSync(path.join(moduleA, 'index.js'),
+                 'module.exports = {b: require(\'moduleB\')};', 'utf8');
+fs.writeFileSync(path.join(moduleB, 'index.js'),
+                 'module.exports = {a: require(\'moduleA\')};', 'utf8');
+
+// Ensure that the symlinks are not followed forever...
+const obj = require(path.join(tmpDir, 'index'));
+assert.ok(obj);
+assert.ok(obj.b);
+assert.ok(obj.b.a);
+assert.ok(!obj.b.a.b);