Enable flake8-pyi plugin to automatically include *.pyi files

This simplifies running flake8 tests and reduces the amount of F821 errors
reported (flake8-pyi enables support for forward references in *.pyi files).
The error code is left disabled until I clean up the remaining issues.

.flake8

@@ -15,7 +15,11 @@
 
 [flake8]
 ignore = F401, F811, F821, E127, E128, E301, E302, E305, E501, E701, E704, E999, B303
+# We are checking with Python 3 but many of the stubs are Python 2 stubs.
+# A nice future improvement would be to provide separate .flake8
+# configurations for Python 2 and Python 3 files.
+builtins = StandardError,apply,basestring,buffer,cmp,coerce,execfile,file,intern,long,raw_input,reduce,reload,unichr,unicode,xrange
 
 # Errors that we need to fix before enabling flake8 by default:
-#   936 F821 undefined name - FIXME: re-enable and add missing imports
+#   208 F821 undefined name - FIXME: re-enable and add missing imports
 #     6 E999 invalid syntax - FIXME: re-enable after flake8 is running from Python 3.6

.travis.yml

@@ -4,15 +4,15 @@ language: python
 matrix:
   include:
     - python: "3.5"
-      env: TEST_CMD="./tests/flake8_test.py"
+      env: TEST_CMD="flake8"
     - python: "3.5"
       env: TEST_CMD="./tests/mypy_test.py"
     - python: "2.7"
       env: TEST_CMD="./tests/pytype_test.py --num-parallel=4"
 
 install:
   # pytype needs py-2.7, mypy needs py-3.2+. Additional logic in runtests.py
-  - if [[ $TRAVIS_PYTHON_VERSION == '3.5' ]]; then pip install -U git+git://github.com/python/mypy git+git://github.com/dropbox/typed_ast flake8-bugbear; fi
+  - if [[ $TRAVIS_PYTHON_VERSION == '3.5' ]]; then pip install -U git+git://github.com/python/mypy git+git://github.com/dropbox/typed_ast flake8==3.2.1 flake8-bugbear flake8-pyi; fi
   - if [[ $TRAVIS_PYTHON_VERSION == '2.7' ]]; then pip install -U git+git://github.com/google/pytype; fi
 
 script:

README.md

@@ -116,7 +116,7 @@ mypy tests and flake8 tests by invoking:
 ```
 (.venv3)$ python tests/mypy_test.py
 ...
-(.venv3)$ python tests/flake8_test.py
+(.venv3)$ flake8
 ...
 ```
 To run the pytype tests, you need a separate virtual environment with
@@ -146,7 +146,7 @@ running mypy --python-version 3.2 --strict-optional # with 453 files
 running mypy --python-version 2.7 --strict-optional # with 502 files
 Running pytype tests...
 Ran pytype with 244 pyis, got 0 errors.
-Running flake8 on 886 .pyi files...
+Running flake8...
 flake8 run clean.
 (.venv3)$
 ```

requirements-tests-py3.txt

@@ -1,4 +1,5 @@
 mypy-lang>=0.4.6
 typed-ast>=0.6.1
-flake8>=3.2.1
+flake8==3.2.1
 flake8-bugbear>=16.12.2
+flake8-pyi>=16.12.0

runtests.sh

@@ -2,4 +2,5 @@
 
 ./tests/mypy_test.py
 ./tests/pytype_test.py
-./tests/flake8_test.py
+echo "Running flake8..."
+flake8 && echo "flake8 run clean."

tests/mypy_test.py

@@ -126,7 +126,7 @@ def main():
             flags.append('--strict-optional')
             if (major, minor) >= (3, 6):
                 flags.append('--fast-parser')
-            ##flags.append('--warn-unused-ignores')  # Fast parser and regular parser disagree.
+            # flags.append('--warn-unused-ignores')  # Fast parser and regular parser disagree.
             sys.argv = ['mypy'] + flags + files
             if args.verbose:
                 print("running", ' '.join(sys.argv))