Add initial mypy configuration and types

As a first step, add type hints to variables whose type `mypy` cannot
infer automatically. This is the minimal set of type hints that allow
running `mypy` without any arguments, and having it not fail.

We currently ignore C extensions that mypy can't process directly.
Later, we can look into generating stubs for such modules (potentially
automatically).

2 files changed, 4 insertions, 3 deletions

diff --git a/src/buildstream/testing/__init__.py b/src/buildstream/testing/__init__.py
index 5a034cf30..3926b4eab 100644
--- a/src/buildstream/testing/__init__.py
+++ b/src/buildstream/testing/__init__.py
@@ -38,7 +38,7 @@ except ImportError:
 
 
 # Of the form plugin_name -> (repo_class, plugin_package)
-ALL_REPO_KINDS = OrderedDict()
+ALL_REPO_KINDS = OrderedDict()  # type: OrderedDict[Repo, str]
 
 
 def create_repo(kind, directory, subdir='repo'):
diff --git a/src/buildstream/testing/_utils/site.py b/src/buildstream/testing/_utils/site.py
index d51d37525..b098b7d41 100644
--- a/src/buildstream/testing/_utils/site.py
+++ b/src/buildstream/testing/_utils/site.py
@@ -5,13 +5,14 @@ import os
 import subprocess
 import sys
 import platform
+from typing import Optional   # pylint: disable=unused-import
 
 from buildstream import _site, utils, ProgramNotFoundError
 from buildstream._platform import Platform
 
 
 try:
-    GIT = utils.get_host_tool('git')
+    GIT = utils.get_host_tool('git')    # type: Optional[str]
     HAVE_GIT = True
 
     out = str(subprocess.check_output(['git', '--version']), "utf-8")
@@ -33,7 +34,7 @@ except ProgramNotFoundError:
     GIT_ENV = dict()
 
 try:
-    BZR = utils.get_host_tool('bzr')
+    BZR = utils.get_host_tool('bzr')    # type: Optional[str]
     HAVE_BZR = True
     BZR_ENV = {
         "BZR_EMAIL": "Testy McTesterson <testy.mctesterson@example.com>"