Resolve symlinked modules correctly

.travis.yml

@@ -1,7 +1,5 @@
 language: node_js
 node_js:
-    - "0.8"
-    - "0.10"
-    - "4"
-    - "5"
-    - "6"
+  - "8"
+  - "10"
+  - "12"

index.js

@@ -206,7 +206,7 @@ function build_resolve_opts(opts, base) {
     return opts;
 }
 
-function resolve(id, opts, cb) {
+function resolve(id, opts, callback) {
 
     // opts.filename
     // opts.paths
@@ -216,6 +216,24 @@ function resolve(id, opts, cb) {
     opts = opts || {};
     opts.filename = opts.filename || '';
 
+    var cb = function(err, path, pkg) {
+        fs.stat(path, function(notPath) {
+            if (notPath) {
+                callback(err, path, pkg);
+            }
+            else {
+                fs.realpath(path, function(notReal, real) {
+                    if (notReal) {
+                        callback(err, path, pkg);
+                    }
+                    else {
+                        callback(err, real, pkg);
+                    }
+                });
+            }
+        });
+    }
+
     var base = path.dirname(opts.filename);
 
     if (opts.basedir) {

package.json

@@ -8,7 +8,7 @@
     "empty.js"
   ],
   "scripts": {
-    "test": "mocha --reporter list test/*.js"
+    "test": "node scripts/setup-symlinks.js && mocha --reporter list test/*.js"
   },
   "repository": {
     "type": "git",

scripts/setup-symlinks.js

@@ -0,0 +1,10 @@
+var fs = require('fs');
+
+try {
+  fs.mkdirSync(__dirname + '/../test/fixtures/node_modules/linker/node_modules');
+} catch (e) {}
+process.chdir(__dirname + '/../test/fixtures/node_modules/linker/node_modules');
+try {
+  fs.unlinkSync('linked');
+} catch (e) {}
+fs.symlinkSync('../../../linked', 'linked', 'dir');

test/fixtures/linked/index.js

@@ -0,0 +1 @@
+// dummy

test/modules.js

@@ -319,3 +319,25 @@ test('not fail on accessing path name defined in Object.prototype', function (do
         done();
     });
 });
+
+test('respect symlinks', function (done) {
+    // some systems (e.g. rush, pnpm) use symlinks to create a recursive dependency graph
+    // instead of relying on the hoisting aspect of the node module resolution algorithm (like npm and yarn do)
+    // in these cases, we want to resolve to the real path of a module, so that the tree structure below
+    // only ever tries to run the `x` module once (rather than once on each module that depends on it)
+    //
+    // - node_modules
+    //   - a
+    //     - node_modules
+    //       - symlink to x
+    //   - b
+    //     - node_modules
+    //       - symlink to x
+    //
+    resolve('linked', { paths: [ fixtures_dir + '/linker/node_modules' ], package: { main: 'fixtures' } }, function(err, path, pkg) {
+        assert.ifError(err);
+        assert.equal(path, require.resolve('./fixtures/linked/index'));
+        assert.strictEqual(pkg, undefined);
+        done();
+    });
+});