Use Travis CI to run tests on every pull request

This is a second attempt at nodejs#1336 which got into a bad git-state...

Use flake8 to find Python syntax errors and undefined names.  There are Python 3 syntax errors and many undefined names which may raise NameError at runtime. This PR runs flake8 runs in two passes: The first looks at critical issues in stop-the-build mode and the second looks at style violations in everything-is-a-warning mode.

.travis.yml

@@ -0,0 +1,24 @@
+dist: xenial
+language: python
+cache: pip
+python:
+    - 2.7
+    - 3.7
+matrix:
+    allow_failures:
+        - python: 3.7
+install:
+    #- pip install -r requirements.txt
+    - pip install flake8  # pytest  # add another testing frameworks later
+before_script:
+    # stop the build if there are Python syntax errors or undefined names
+    - flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics
+    # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide
+    - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+    - npm install
+script:
+    - npm test
+    #- pytest --capture=sys  # add other tests here
+notifications:
+    on_success: change
+    on_failure: change  # `always` will be the setting once code changes slow down

gyp/pylib/gyp/MSVSVersion.py

@@ -178,15 +178,15 @@ def _RegistryGetValueUsingWinReg(key, value):
   """
   try:
       # Python 2
-      from _winreg import OpenKey, QueryValueEx
+      from _winreg import HKEY_LOCAL_MACHINE, OpenKey, QueryValueEx
   except ImportError:
       # Python 3
-      from winreg import OpenKey, QueryValueEx
+      from winreg import HKEY_LOCAL_MACHINE, OpenKey, QueryValueEx
 
   try:
     root, subkey = key.split('\\', 1)
     assert root == 'HKLM'  # Only need HKLM for now.
-    with OpenKey(_winreg.HKEY_LOCAL_MACHINE, subkey) as hkey:
+    with OpenKey(HKEY_LOCAL_MACHINE, subkey) as hkey:
       return QueryValueEx(hkey, value)[0]
   except WindowsError:
     return None

gyp/pylib/gyp/input.py

@@ -1182,7 +1182,7 @@ def LoadVariablesFromVariablesDict(variables, the_dict, the_dict_key):
       if variable_name in variables:
         # If the variable is already set, don't set it.
         continue
-      if the_dict_key is 'variables' and variable_name in the_dict:
+      if the_dict_key == 'variables' and variable_name in the_dict:
         # If the variable is set without a % in the_dict, and the_dict is a
         # variables dict (making |variables| a varaibles sub-dict of a
         # variables dict), use the_dict's definition.

gyp/pylib/gyp/xcode_emulation.py

@@ -844,7 +844,7 @@ def GetLdflags(self, configname, product_dir, gyp_to_build_path, arch=None):
     if self._IsXCTest():
       platform_root = self._XcodePlatformPath(configname)
       if platform_root:
-        cflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')
+        cflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')  # noqa TODO @cclauss
 
     is_extension = self._IsIosAppExtension() or self._IsIosWatchKitExtension()
     if sdk_root and is_extension: