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>

7 files changed, 43 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index 3c64ffabe0..8b87e4d858 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,7 @@
 *~
 .autogenerated
 .coverage
+.mypy_cache
 .nova-venv
 .project
 .pydevproject
diff --git a/lower-constraints.txt b/lower-constraints.txt
index 45fb9b9d5c..d1134653b1 100644
--- a/lower-constraints.txt
+++ b/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
diff --git a/mypy-files.txt b/mypy-files.txt
new file mode 100644
index 0000000000..4ee414816e
--- /dev/null
+++ b/mypy-files.txt
@@ -0,0 +1 @@
+nova/virt/libvirt/__init__.py
diff --git a/setup.cfg b/setup.cfg
index c89f1999a4..6356fc74c2 100644
--- a/setup.cfg
+++ b/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
diff --git a/test-requirements.txt b/test-requirements.txt
index 25ac29b7ef..d42fb05f18 100644
--- a/test-requirements.txt
+++ b/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
diff --git a/tools/mypywrap.sh b/tools/mypywrap.sh
new file mode 100644
index 0000000000..dd5868d6e2
--- /dev/null
+++ b/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
diff --git a/tox.ini b/tox.ini
index 214a8c75f5..5402c7edab 100644
--- a/tox.ini
+++ b/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'"