WebUI: Hook up ESLint to web_dev_style PRESUBMIT.

tools/web_dev_style/js_checker.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Presubmit script for Chromium JS resources.
 
 See chrome/browser/PRESUBMIT.py
 """
 
 import regex_check
@@ skipping 50 matching lines @@
   def InheritDocCheck(self, i, line):
     """Checks for use of '@inheritDoc' instead of '@override'."""
     return self.RegexCheck(i, line, r"\* (@inheritDoc)",
         "@inheritDoc is deprecated, use @override instead")
 
   def PolymerLocalIdCheck(self, i, line):
     """Checks for use of element.$.localId."""
     return self.RegexCheck(i, line, r"(?<!this)(\.\$)[\[\.]",
         "Please only use this.$.localId, not element.$.localId")
 
+  def RunEsLintChecks(self, affected_js_files):
+    """Runs lint checks using ESLint. The ESLint rules being applied are defined
+       in the .eslintrc.js configuration file.
+    """
+    os_path = self.input_api.os_path
+
+    try:
+      # Import ESLint.
+      _HERE_PATH = os_path.dirname(os_path.realpath(__file__))

[Dan Beam, 2017/05/25 01:01:20]

why do you need to call realpath?

[dpapad, 2017/05/25 01:11:56]

I might not need to, not sure if calling realpath() has any benefit.

A quick search (both within Chromium and outside) shows that this is pretty
common,

For example see
https://cs.chromium.org/search/?q=%22os.path.dirname(os.path.realpath(__file_...

The equivalent without realpath is also common,
https://cs.chromium.org/search/?q=%22os.path.dirname(__file__)%22&type=cs

+      _SRC_PATH = os_path.normpath(os_path.join(_HERE_PATH, '..', '..'))
+      import sys
+      old_sys_path = sys.path[:]
+      sys.path.append(os_path.join(_SRC_PATH, 'third_party', 'node'))
+      import node, node_modules
+    finally:
+      sys.path = old_sys_path
+
+    # Extract paths to be passed to ESLint.
+    affected_js_files_paths = []
+    presubmit_path = self.input_api.PresubmitLocalPath()
+    for f in affected_js_files:
+      affected_js_files_paths.append(
+          os_path.relpath(f.AbsoluteLocalPath(), presubmit_path))
+
+    output = node.RunNode([
+        node_modules.PathToEsLint(),
+        '--color',
+        '--ignore-pattern \'!.eslintrc.js\'',
+        ' '.join(affected_js_files_paths)])
+
+    return [self.output_api.PresubmitError(output)] if output else []
+
   def WrapperTypeCheck(self, i, line):
     """Check for wrappers (new String()) instead of builtins (string)."""
     return self.RegexCheck(i, line,
         r"(?:/\*)?\*.*?@(?:param|return|type) ?"     # /** @param/@return/@type
         r"{[^}]*\b(String|Boolean|Number)\b[^}]*}",  # {(Boolean|Number|String)}
         "Don't use wrapper types (i.e. new String() or @type {String})")
 
   def VarNameCheck(self, i, line):
     """See the style guide. http://goo.gl/eQiXVW"""
     return self.RegexCheck(i, line,
         r"var (?!g_\w+)(_?[a-z][a-zA-Z]*[_$][\w_$]*)(?<! \$)",
         "Please use var namesLikeThis <https://goo.gl/eQiXVW>")
 
   def _GetErrorHighlight(self, start, length):
     """Takes a start position and a length, and produces a row of '^'s to
        highlight the corresponding part of a string.
     """
     return start * ' ' + length * '^'
 
   def RunChecks(self):
     """Check for violations of the Chromium JavaScript style guide. See
        https://chromium.googlesource.com/chromium/src/+/master/styleguide/web/web.md#JavaScript
     """
     results = []
 
     affected_files = self.input_api.AffectedFiles(file_filter=self.file_filter,
                                                   include_deletes=False)
     affected_js_files = filter(lambda f: f.LocalPath().endswith('.js'),
                                affected_files)
+
+    if affected_js_files:
+      results += self.RunEsLintChecks(affected_js_files)
+
     for f in affected_js_files:
       error_lines = []
 
       for i, line in enumerate(f.NewContents(), start=1):
         error_lines += filter(None, [
             self.ChromeSendCheck(i, line),
             self.CommentIfAndIncludeCheck(i, line),
             self.ConstCheck(i, line),
             self.GetElementByIdCheck(i, line),
             self.EndJsDocCommentCheck(i, line),
             self.ExtraDotInGenericCheck(i, line),
             self.InheritDocCheck(i, line),
             self.PolymerLocalIdCheck(i, line),
             self.WrapperTypeCheck(i, line),
             self.VarNameCheck(i, line),
         ])
 
       if error_lines:
         error_lines = [
             'Found JavaScript style violations in %s:' %
             f.LocalPath()] + error_lines
         results.append(self.output_api.PresubmitError('\n'.join(error_lines)))
 
     if results:
       results.append(self.output_api.PresubmitNotifyResult(
           'See the JavaScript style guide at '
           'https://chromium.googlesource.com/chromium/src/+/master/styleguide/web/web.md#JavaScript'))
 
     return results