set up mypy hook for incremental adoption

.pre-commit-config.yaml

@@ -16,6 +16,21 @@ repos:
               | ^poetry/core/_vendor
           )
 
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v0.910
+    hooks:
+      - id: mypy
+        additional_dependencies:
+          - types-requests
+        files: |
+          (?x)(
+            ^poetry
+          )
+        exclude: |
+          (?x)(
+              ^poetry/core/_vendor
+          )
+
   - repo: https://github.com/pycqa/isort
     rev: 5.9.3
     hooks:

mypy.ini

@@ -0,0 +1,37 @@
+[mypy]
+follow_imports = silent
+
+# The following whitelist is used to allow for incremental adoption
+# of Mypy. Modules should be removed from this whitelist as and when
+# their respective type errors have been addressed. No new modules
+# should be added to this whitelist.
+# see https://github.com/python-poetry/poetry-core/pull/199.
+
+[mypy-poetry.core.factory.*]
+ignore_errors = True
+
+[mypy-poetry.core.masonry.*]
+ignore_errors = True
+
+[mypy-poetry.core.packages.*]
+ignore_errors = True
+
+[mypy-poetry.core.poetry.*]
+ignore_errors = True
+
+[mypy-poetry.core.pyproject.*]
+ignore_errors = True
+
+[mypy-poetry.core.semver.*]
+ignore_errors = True
+
+[mypy-poetry.core.spdx.*]
+ignore_errors = True
+
+[mypy-poetry.core.vcs.*]
+ignore_errors = True
+
+[mypy-poetry.core.version.*]
+ignore_errors = True
+
+# end of whitelist

poetry/__init__.py

@@ -1,4 +1,5 @@
 from pkgutil import extend_path
+from typing import List
 
 
-__path__ = extend_path(__path__, __name__)
+__path__: List[str] = extend_path(__path__, __name__)

poetry/core/utils/helpers.py

@@ -4,22 +4,18 @@
 import stat
 import tempfile
 
+from collections.abc import Mapping
 from contextlib import contextmanager
 from pathlib import Path
 from typing import Any
 from typing import Iterator
 from typing import List
 from typing import Union
+from typing import no_type_check
 
 from poetry.core.version.pep440 import PEP440Version
 
 
-try:
-    from collections.abc import Mapping
-except ImportError:
-    from collections import Mapping
-
-
 _canonicalize_regex = re.compile(r"[-_]+")
 
 
@@ -42,6 +38,7 @@ def temporary_directory(*args: Any, **kwargs: Any) -> Iterator[str]:
     safe_rmtree(name)
 
 
+@no_type_check
 def parse_requires(requires: str) -> List[str]:
     lines = requires.split("\n")