typing: minimal changes to make a no-op mypy run pass

.gitignore

@@ -12,3 +12,4 @@ archives/
 build/
 dist/
 .tox/
+.mypy_cache/

MANIFEST.in

@@ -3,3 +3,4 @@ include requirements.txt
 include requirements-swh.txt
 include version.txt
 recursive-include swh/loader/svn/tests/resources *
+recursive-include swh py.typed

mypy.ini

+[mypy]
+namespace_packages = True
+warn_unused_ignores = True
+
+
+# 3rd party libraries without stubs (yet)
+
+[mypy-celery.*]
+ignore_missing_imports = True
+
+[mypy-subvertpy.*]
+ignore_missing_imports = True

swh/__init__.py

-__path__ = __import__('pkgutil').extend_path(__path__, __name__)
+from pkgutil import extend_path
+from typing import Iterable
+
+__path__ = extend_path(__path__, __name__)  # type: Iterable[str]

swh/loader/__init__.py

-__path__ = __import__('pkgutil').extend_path(__path__, __name__)
+from pkgutil import extend_path
+from typing import Iterable
+
+__path__ = extend_path(__path__, __name__)  # type: Iterable[str]

swh/loader/svn/py.typed

+# Marker file for PEP 561.

tox.ini

 [tox]
-envlist=flake8,py3
+envlist=flake8,mypy,py3
 
 [testenv:py3]
 deps =
@@ -16,3 +16,11 @@ deps =
   flake8
 commands =
   {envpython} -m flake8
+
+[testenv:mypy]
+skip_install = true
+deps =
+  .[testing]
+  mypy
+commands =
+  mypy swh