Test type stubs with stubtest

Author: jorio

Diff for: build.sh

@@ -236,9 +236,19 @@ fi
 
 # Tests
 if [ "$1" = "test" ]; then
+    shift
     if [ -n "$WHEELDIR" ]; then
         $PREFIX/bin/pip install $WHEELDIR/pygit2*-$PYTHON_TAG-*.whl
     fi
     $PREFIX/bin/pip install -r requirements-test.txt
     $PREFIX/bin/pytest --cov=pygit2
 fi
+
+# Test .pyi stub file
+if [ "$1" = "stubtest" ]; then
+    shift
+    $PREFIX/bin/pip install mypy
+    PYTHONPATH=. $PREFIX/bin/stubtest --mypy-config-file mypy-stubtest.ini pygit2._pygit2
+    [ $? == 0 ] && echo "stubtest OK"
+fi
+

Diff for: mypy-stubtest.ini

@@ -0,0 +1,16 @@
+# Config file for testing the stub file (_pygit2.pyi) with "stubtest"
+# (tool shipped with mypy).
+#
+# Run "build.sh stubtest", or:
+#   stubtest --mypy-config-file test/mypy-stubtest.ini pygit2._pygit2
+#
+# Format info:
+#   https://mypy.readthedocs.io/en/stable/config_file.html
+
+[mypy]
+warn_unused_configs = True
+disallow_any_explicit = True
+
+# don't follow import pygit2 from _pygit2.pyi, we only want to check the pyi file.
+[mypy-pygit2]
+follow_imports = skip