WebUI: Hook up ESLint to web_dev_style PRESUBMIT.

tools/web_dev_style/js_checker.py

Index: tools/web_dev_style/js_checker.py
diff --git a/tools/web_dev_style/js_checker.py b/tools/web_dev_style/js_checker.py
index a42a1a22aeef70d5e538bde352d2f0fac7aaf38a..82a69da78f714e7d09e75e7ee5ce9da706fb7549 100644
--- a/tools/web_dev_style/js_checker.py
+++ b/tools/web_dev_style/js_checker.py
@@ -68,6 +68,39 @@ class JSChecker(object):
     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.
+    """
+    # Import ESLint.
+    try:
+      import os

[Dan Beam, 2017/05/24 22:57:53]

use self.input_api.os_path instead of `import os`

[dpapad, 2017/05/24 23:46:02]

Done.

+      _HERE_PATH = os.path.dirname(os.path.realpath(__file__))

[Dan Beam, 2017/05/24 22:57:53]

i'm not totalllly sure how __file__ works here, but can you use

input_api.PresubmitLocalPath() instead maybe?

__file__ doesn't exist when eval()'d

[dpapad, 2017/05/24 23:46:02]

input_api.PresubmitLocalPath() returns the location of the current PRESUBMIT.py
file, not the location of js_checker.py file, which is what needed here.

For example when modifying a file inside chrome/browser/resources/settings/, it
would return chrome/browser/resources/ (because that's where the PRESUBMIT.py
file resides).

Is js_checker.py ever invoked with eval()? I have been using 'git cl presubmit'
to test my changes locally and that line seems to always work as expected.

[Dan Beam, 2017/05/25 00:14:51]

probably not.  if it works for now with `git cl presubmit` it's probably fine

+      _SRC_PATH = os.path.normpath(os.path.join(_HERE_PATH, '..', '..'))
+      import sys
+      _NODE_PATH = os.path.join(_SRC_PATH, 'third_party', 'node')
+      old_path = sys.path[::]

[Dan Beam, 2017/05/24 23:01:34]

nit: [::] -> [:]

[dpapad, 2017/05/24 23:46:02]

Done.

+      sys.path.append(os.path.join(_SRC_PATH, 'third_party', 'node'))
+      import node
+      import node_modules

[Dan Beam, 2017/05/24 23:01:34]

import node, node_modules

[dpapad, 2017/05/24 23:46:02]

Done.

+    finally:
+      sys.path = old_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,
@@ -97,6 +130,10 @@ class JSChecker(object):
                                                   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 = []