Provide a quick way to run flake8

"run_tests.sh -p" always checks every file for errors even though you
have probably only changed a handful. This patch adds "run_tests.sh -8"
which only checks the files that were modified in the HEAD commit or
in the current working tree.

It is borrowed from the recent nova commit b011325cc6.
The related ML post is:
http://lists.openstack.org/pipermail/openstack-dev/2014-August/043346.html

Change-Id: Ieeabf1b79a0790af8bde3144dca59b4245a0b79a

run_tests.sh

@@ -14,6 +14,8 @@ function usage {
   echo "  -f, --force                 Force a clean re-build of the virtual environment. Useful when dependencies have been added."
   echo "  -u, --update                Update the virtual environment with any newer package versions"
   echo "  -p, --pep8                  Just run PEP8 and HACKING compliance check"
+  echo "  -8, --pep8-only-changed [<basecommit>]"
+  echo "                              Just run PEP8 and HACKING compliance check on files changed since HEAD~1 (or <basecommit>)"
   echo "  -P, --no-pep8               Don't run static code checks"
   echo "  -c, --coverage              Generate coverage report"
   echo "  -d, --debug                 Run tests with testtools instead of testr. This allows you to use the debugger."
@@ -44,6 +46,7 @@ function process_options {
       -f|--force) force=1;;
       -u|--update) update=1;;
       -p|--pep8) just_pep8=1;;
+      -8|--pep8-only-changed) just_pep8_changed=1;;
       -P|--no-pep8) no_pep8=1;;
       -c|--coverage) coverage=1;;
       -d|--debug) debug=1;;
@@ -59,8 +62,8 @@ function process_options {
         (( i++ ))
         tools_path=${!i}
         ;;
-      -*) testropts="$testropts ${!i}";;
-      *) testrargs="$testrargs ${!i}"
+      -*) testopts="$testopts ${!i}";;
+      *) testargs="$testargs ${!i}"
     esac
     (( i++ ))
   done
@@ -75,10 +78,11 @@ never_venv=0
 force=0
 no_site_packages=0
 installvenvopts=
-testrargs=
-testropts=
+testargs=
+testopts=
 wrapper=""
 just_pep8=0
+just_pep8_changed=0
 no_pep8=0
 coverage=0
 debug=0
@@ -107,12 +111,12 @@ function run_tests {
   ${wrapper} find . -type f -name "*.pyc" -delete
 
   if [ $debug -eq 1 ]; then
-    if [ "$testropts" = "" ] && [ "$testrargs" = "" ]; then
+    if [ "$testopts" = "" ] && [ "$testargs" = "" ]; then
       # Default to running all tests if specific test is not
       # provided.
-      testrargs="discover ./neutron/tests"
+      testargs="discover ./neutron/tests"
     fi
-    ${wrapper} python -m testtools.run $testropts $testrargs
+    ${wrapper} python -m testtools.run $testopts $testargs
 
     # Short circuit because all of the testr and coverage stuff
     # below does not make sense when running testtools.run for
@@ -128,9 +132,9 @@ function run_tests {
 
   # Just run the test suites in current environment
   set +e
-  testrargs=`echo "$testrargs" | sed -e's/^\s*\(.*\)\s*$/\1/'`
-  TESTRTESTS="$TESTRTESTS --testr-args='--subunit $testropts $testrargs'"
-  OS_TEST_PATH=`echo $testrargs|grep -o 'neutron\.tests[^[:space:]:]*\+'|tr . /`
+  testargs=`echo "$testargs" | sed -e's/^\s*\(.*\)\s*$/\1/'`
+  TESTRTESTS="$TESTRTESTS --testr-args='--subunit $testopts $testargs'"
+  OS_TEST_PATH=`echo $testargs|grep -o 'neutron\.tests[^[:space:]:]*\+'|tr . /`
   if [ -d "$OS_TEST_PATH" ]; then
       wrapper="OS_TEST_PATH=$OS_TEST_PATH $wrapper"
   elif [ -d "$(dirname $OS_TEST_PATH)" ]; then
@@ -160,12 +164,32 @@ function copy_subunit_log {
   cp $LOGNAME subunit.log
 }
 
+function warn_on_flake8_without_venv {
+  if [ $never_venv -eq 1 ]; then
+    echo "**WARNING**:"
+    echo "Running flake8 without virtual env may miss OpenStack HACKING detection"
+  fi
+}
+
 function run_pep8 {
   echo "Running flake8 ..."
-
+  warn_on_flake8_without_venv
   ${wrapper} flake8
 }
 
+function run_pep8_changed {
+    # NOTE(gilliard) We want use flake8 to check the entirety of every file that has
+    # a change in it. Unfortunately the --filenames argument to flake8 only accepts
+    # file *names* and there are no files named (eg) "nova/compute/manager.py".  The
+    # --diff argument behaves surprisingly as well, because although you feed it a
+    # diff, it actually checks the file on disk anyway.
+    local target=${testargs:-HEAD~1}
+    local files=$(git diff --name-only $target | tr '\n' ' ')
+    echo "Running flake8 on ${files}"
+    warn_on_flake8_without_venv
+    diff -u --from-file /dev/null ${files} | ${wrapper} flake8 --diff
+}
+
 
 TESTRTESTS="python -m neutron.openstack.common.lockutils python setup.py testr"
 
@@ -209,6 +233,11 @@ if [ $just_pep8 -eq 1 ]; then
     exit
 fi
 
+if [ $just_pep8_changed -eq 1 ]; then
+    run_pep8_changed
+    exit
+fi
+
 if [ $recreate_db -eq 1 ]; then
     rm -f tests.sqlite
 fi
@@ -217,9 +246,9 @@ run_tests
 
 # NOTE(sirp): we only want to run pep8 when we're running the full-test suite,
 # not when we're running tests individually. To handle this, we need to
-# distinguish between options (testropts), which begin with a '-', and
-# arguments (testrargs).
-if [ -z "$testrargs" ]; then
+# distinguish between options (testopts), which begin with a '-', and
+# arguments (testargs).
+if [ -z "$testargs" ]; then
   if [ $no_pep8 -eq 0 ]; then
     run_pep8
   fi