Fix #3394 fs.realpath: Properly cache symlink targets

lib/fs.js

@@ -962,21 +962,21 @@ fs.realpathSync = function realpathSync(p, cache) {
 
       // read the link if it wasn't read before
       // dev/ino always return 0 on windows, so skip the check.
-      var linkTarget;
+      var linkTarget = null;
       if (!isWindows) {
         var id = stat.dev.toString(32) + ':' + stat.ino.toString(32);
-        if (seenLinks[id]) {
+        if (seenLinks.hasOwnProperty(id)) {
           linkTarget = seenLinks[id];
         }
       }
-      if (!linkTarget) {
+      if (linkTarget === null) {
         fs.statSync(base);
         linkTarget = fs.readlinkSync(base);
-        resolvedLink = pathModule.resolve(previous, linkTarget);
-        // track this, if given a cache.
-        if (cache) cache[base] = resolvedLink;
-        if (!isWindows) seenLinks[id] = linkTarget;
       }
+      resolvedLink = pathModule.resolve(previous, linkTarget);
+      // track this, if given a cache.
+      if (cache) cache[base] = resolvedLink;
+      if (!isWindows) seenLinks[id] = linkTarget;
     }
 
     // resolve the link, then start over
@@ -1071,7 +1071,7 @@ fs.realpath = function realpath(p, cache, cb) {
     // dev/ino always return 0 on windows, so skip the check.
     if (!isWindows) {
       var id = stat.dev.toString(32) + ':' + stat.ino.toString(32);
-      if (seenLinks[id]) {
+      if (seenLinks.hasOwnProperty(id)) {
         return gotTarget(null, seenLinks[id], base);
       }
     }

test/simple/test-fs-realpath.js

@@ -349,6 +349,40 @@ var uponeActual = fs.realpathSync('..');
 assert.equal(upone, uponeActual,
     'realpathSync("..") expected: ' + upone + ' actual:' + uponeActual);
 
+
+// going up with .. multiple times
+// .
+// `-- a/
+//     |-- b/
+//     |   `-- e -> ..
+//     `-- d -> ..
+// realpath(a/b/e/d/a/b/e/d/a) ==> a
+function test_up_multiple(cb) {
+  fs.mkdirSync(common.tmpDir + '/a', 0755);
+  fs.mkdirSync(common.tmpDir + '/a/b', 0755);
+  fs.symlinkSync(common.tmpDir + '/a/d', '..');
+  fs.symlinkSync(common.tmpDir + '/a/b/e', '..');
+
+  var abedabed = tmp('abedabed'.split('').join('/'));
+  var abedabeda_real = tmp('');
+
+  var abedabeda = tmp('abedabeda'.split('').join('/'));
+  var abedabeda_real = tmp('a');
+
+  assert.equal(fs.realpathSync(abedabeda), abedabeda_real);
+  assert.equal(fs.realpathSync(abedabed), abedabed_real);
+  fs.realpath(abedabeda, function (er, real) {
+    if (er) throw er;
+    assert.equal(abedabeda_real, real);
+    fs.realpath(abedabed, function (er, real) {
+      if (er) throw er;
+      assert.equal(abedabed_real, real);
+      cb();
+    });
+  });
+}
+
+
 // absolute symlinks with children.
 // .
 // `-- a/