src,module: add --preserve-symlinks command line flag

Add the `--preserve-symlinks` flag. This makes the changes added
in #5950 conditional. By default the old behavior is used. With
the flag set, symlinks are preserved, switching to the new
behavior. This should be considered to be a temporary solution
until we figure out how to solve the symlinked peer dependency
problem in a more general way that does not break everything
else.

Additional test cases are included.

PR-URL: https://github.com/nodejs/node/pull/6537
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

1 files changed, 65 insertions, 0 deletions

diff --git a/test/parallel/test-module-symlinked-peer-modules.js b/test/parallel/test-module-symlinked-peer-modules.js
new file mode 100644
index 0000000000..83aca75ed1
--- /dev/null
+++ b/test/parallel/test-module-symlinked-peer-modules.js
@@ -0,0 +1,65 @@
+// Flags: --preserve-symlinks
+'use strict';
+// Refs: https://github.com/nodejs/node/pull/5950
+
+// This test verifies that symlinked modules are able to find their peer
+// dependencies when using the --preserve-symlinks command line flag.
+
+// This test passes in v6.2+ with --preserve-symlinks on and in v6.0/v6.1.
+// This test will fail in Node.js v4 and v5 and should not be backported.
+
+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;
+  common.skip('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');
+
+assert.doesNotThrow(() => {
+  require(path.join(app, 'index'));
+});