tox: make it possible to run pep8 on current patch only

This makes tox use a simple wrapper around flake8 like
Nova, which can be told to restrict the check to only
files changed in the current command. This can be invoked
in a simple manner with 'tox -epep8 -- -HEAD'. Since most
commits only touch a handful of files, this will usually
be far faster than checking all source files.

To check an entire branch for bisectability it can be
automated via

  git rebase -i master -x 'tox -epep8 -- -HEAD'

Change-Id: I75b1cfe3198b1217f8b25877714a4af47ae7069f

1 files changed, 20 insertions, 0 deletions

diff --git a/tools/flake8wrap.sh b/tools/flake8wrap.sh
new file mode 100755
index 000000000..531b407d6
--- /dev/null
+++ b/tools/flake8wrap.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+#
+# A simple wrapper around flake8 which makes it possible
+# to ask it to only verify files changed in the current
+# git HEAD patch.
+#
+# Intended to be invoked via tox:
+#
+#   tox -epep8 -- -HEAD
+#
+
+if test "x$1" = "x-HEAD" ; then
+    shift
+    files=$(git diff --name-only HEAD~1 | tr '\n' ' ')
+    echo "Running flake8 on ${files}"
+    diff -u --from-file /dev/null ${files} | flake8 --diff "$@"
+else
+    echo "Running flake8 on all files"
+    exec flake8 "$@"
+fi