tox: Integrate mypy

mypy is an experimental optional static type checker for Python that
aims to combine the benefits of dynamic (or "duck") typing and static
typing. While still in development, most features are supported and it's
already being used by real world projects like Sphinx. Let's start small
by integrating it into some of the interfaces that nova exposes. We can
further build upon this if it works out.

This change sets up the boilerplate necessary to use mypy in nova. Type
annotations are not included for any module - these will be added
separately. We're calling mypy by way of a script, as this allows us to
store a list of files that we have converted while we're in the process
of adding type annotations where necessary.

Change-Id: I75ab46a6768c4ca2050fdde2b7f8eeb90724c8c6
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

.gitignore

@@ -9,6 +9,7 @@
 *~
 .autogenerated
 .coverage
+.mypy_cache
 .nova-venv
 .project
 .pydevproject

lower-constraints.txt

@@ -57,6 +57,7 @@ monotonic==1.4
 msgpack==0.5.6
 msgpack-python==0.5.6
 munch==2.2.0
+mypy==0.761
 netaddr==0.7.18
 netifaces==0.10.4
 networkx==1.11

mypy-files.txt

@@ -0,0 +1 @@
+nova/virt/libvirt/__init__.py

setup.cfg

@@ -84,3 +84,12 @@ console_scripts =
 wsgi_scripts =
     nova-api-wsgi = nova.api.openstack.compute.wsgi:init_application
     nova-metadata-wsgi = nova.api.metadata.wsgi:init_application
+
+[mypy]
+show_column_numbers = true
+show_error_context = true
+ignore_missing_imports = true
+follow_imports = skip
+incremental = true
+check_untyped_defs = true
+warn_unused_ignores = true

test-requirements.txt

@@ -3,6 +3,7 @@
 # process, which may cause wedges in the gate later.
 
 hacking>=3.0.1,<3.1.0 # Apache-2.0
+mypy>=0.761 # MIT
 coverage!=4.4,>=4.0 # Apache-2.0
 ddt>=1.0.1 # MIT
 fixtures>=3.0.0 # Apache-2.0/BSD

tools/mypywrap.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+#
+# A wrapper around mypy that allows us to specify what files to run 'mypy' type
+# checks on. Intended to be invoked via tox:
+#
+#   tox -e mypy
+#
+# Eventually this should go away once we have either converted everything or
+# converted enough and ignored [1] the rest.
+#
+# [1] http://mypy.readthedocs.io/en/latest/config_file.html#per-module-flags
+
+ROOT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+if [ $# -eq 0 ]; then
+    # if no arguments provided, use the standard converted lists
+    lines=$(grep -v '#' $ROOT_DIR/../mypy-files.txt)
+    python -m mypy ${lines[@]}
+else
+    # else test what the user asked us to
+    python -m mypy $@
+fi

tox.ini

@@ -38,11 +38,19 @@ commands =
   env TEST_OSPROFILER=1 stestr run --combine --no-discover 'nova.tests.unit.test_profiler'
   stestr slowest
 
+[testenv:mypy]
+description =
+  Run type checks.
+envdir = {toxworkdir}/shared
+commands =
+  bash tools/mypywrap.sh {posargs}
+
 [testenv:pep8]
 description =
   Run style checks.
 envdir = {toxworkdir}/shared
 commands =
+  {[testenv:mypy]commands}
   bash tools/flake8wrap.sh {posargs}
   # Check that all JSON files don't have \r\n in line.
   bash -c "! find doc/ -type f -name *.json | xargs grep -U -n $'\r'"