fs: include filename in watch errors

This commit adds the relevant filename to fs.watch() errors.

Refs: nodejs/node-v0.x-archive#25542
PR-URL: #2748
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/fs.js

@@ -1219,7 +1219,9 @@ function FSWatcher() {
   this._handle.onchange = function(status, event, filename) {
     if (status < 0) {
       self._handle.close();
-      self.emit('error', errnoException(status, 'watch'));
+      const error = errnoException(status, `watch ${filename}`);
+      error.filename = filename;
+      self.emit('error', error);
     } else {
       self.emit('change', event, filename);
     }
@@ -1234,7 +1236,9 @@ FSWatcher.prototype.start = function(filename, persistent, recursive) {
                                recursive);
   if (err) {
     this._handle.close();
-    throw errnoException(err, 'watch');
+    const error = errnoException(err, `watch ${filename}`);
+    error.filename = filename;
+    throw error;
   }
 };
 

test/sequential/test-fs-watch.js

@@ -126,3 +126,20 @@ assert.throws(function() {
   w.stop();
 }, TypeError);
 oldhandle.stop(); // clean up
+
+assert.throws(function() {
+  fs.watch('non-existent-file');
+}, function(err) {
+  assert(err);
+  assert(/non-existent-file/.test(err));
+  assert.equal(err.filename, 'non-existent-file');
+  return true;
+});
+
+var watcher = fs.watch(__filename);
+watcher.on('error', common.mustCall(function(err) {
+  assert(err);
+  assert(/non-existent-file/.test(err));
+  assert.equal(err.filename, 'non-existent-file');
+}));
+watcher._handle.onchange(-1, 'ENOENT', 'non-existent-file');