Bring mypy into the tox config

Author: wsanchez

.gitignore

@@ -3,6 +3,7 @@ tmp.py
 htmlcov/
 .coverage.*
 *.py[cod]
+.mypy_cache
 
 # emacs
 *~

setup.py

@@ -30,7 +30,10 @@
       zip_safe=False,
       license=__license__,
       platforms='any',
-      install_requires=['idna>=2.5'],
+      install_requires=[
+          'idna>=2.5',
+          'typing ; python_version<"3.5"',
+      ],
       classifiers=[
           'Topic :: Utilities',
           'Intended Audience :: Developers',

tox.ini

@@ -31,6 +31,7 @@ basepython =
 deps =
     test: coverage==4.5.4
     test: idna==2.8
+    test: typing==3.7.4.1
     test: {py26,py27,py34}: pytest==4.6.6
     test: {py35,py36,py37,py38}: pytest==5.2.1
     test: pytest-cov==2.8.1
@@ -122,6 +123,74 @@ ignore =
 application-import-names = deploy
 
 
+##
+# Mypy static type checking
+##
+
+[testenv:mypy]
+
+description = run Mypy (static type checker)
+
+basepython = python3.7
+
+skip_install = True
+
+
+deps =
+    mypy==0.730
+
+
+commands =
+    mypy                                       \
+        --config-file="{toxinidir}/tox.ini"    \
+        --cache-dir="{toxworkdir}/mypy_cache"  \
+        {tty:--pretty:}                        \
+        {posargs:src}
+
+
+[mypy]
+
+# Global settings
+
+no_implicit_optional     = True
+show_column_numbers      = True
+show_error_codes         = True
+strict_optional          = True
+warn_no_return           = True
+warn_redundant_casts     = True
+warn_return_any          = True
+warn_unused_ignores      = True
+warn_unreachable         = True
+
+# Enable these over time
+check_untyped_defs       = False
+disallow_incomplete_defs = False
+disallow_untyped_defs    = False
+
+# Disable checks until effected files fully adopt mypy
+
+[mypy-hyperlink._url]
+allow_untyped_defs = True
+
+[mypy-hyperlink.test.common]
+allow_untyped_defs = True
+
+[mypy-hyperlink.test.test_common]
+allow_untyped_defs = True
+
+[mypy-hyperlink.test.test_decoded_url]
+allow_untyped_defs = True
+
+[mypy-hyperlink.test.test_scheme_registration]
+allow_untyped_defs = True
+
+[mypy-hyperlink.test.test_url]
+allow_untyped_defs = True
+
+[mypy-idna]
+ignore_missing_imports = True
+
+
 ##
 # Coverage report
 ##