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, 8 insertions, 6 deletions

diff --git a/lib/module.js b/lib/module.js
index 344ea97af9..ccbb5ba0e0 100644
--- a/lib/module.js
+++ b/lib/module.js
@@ -10,6 +10,7 @@ const fs = require('fs');
 const path = require('path');
 const internalModuleReadFile = process.binding('fs').internalModuleReadFile;
 const internalModuleStat = process.binding('fs').internalModuleStat;
+const preserveSymlinks = !!process.binding('config').preserveSymlinks;
 
 // If obj.hasOwnProperty has been overridden, then calling
 // obj.hasOwnProperty(prop) will break.
@@ -109,14 +110,15 @@ function tryPackage(requestPath, exts, isMain) {
 }
 
 // check if the file exists and is not a directory
-// resolve to the absolute realpath if running main module,
-// otherwise resolve to absolute while keeping symlinks intact.
+// if using --preserve-symlinks and isMain is false,
+// keep symlinks intact, otherwise resolve to the
+// absolute realpath.
 function tryFile(requestPath, isMain) {
   const rc = stat(requestPath);
-  if (isMain) {
-    return rc === 0 && fs.realpathSync(requestPath);
+  if (preserveSymlinks && !isMain) {
+    return rc === 0 && path.resolve(requestPath);
   }
-  return rc === 0 && path.resolve(requestPath);
+  return rc === 0 && fs.realpathSync(requestPath);
 }
 
 // given a path check a the file exists with any of the set extensions
@@ -159,7 +161,7 @@ Module._findPath = function(request, paths, isMain) {
     if (!trailingSlash) {
       const rc = stat(basePath);
       if (rc === 0) {  // File.
-        if (!isMain) {
+        if (preserveSymlinks && !isMain) {
           filename = path.resolve(basePath);
         } else {
           filename = fs.realpathSync(basePath);