Drop support for running libcst using a python 3.6 interpreter (#663)

* Drop support for running libcst using a python 3.6 interpreter

* PR feedback

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.6, 3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.7, 3.8, 3.9, "3.10"]
         parser: [pure, native]
     steps:
     - uses: actions/checkout@v1

README.rst

@@ -125,7 +125,7 @@ For a more detailed usage example, `see our documentation
 Installation
 ------------
 
-LibCST requires Python 3.6+ and can be easily installed using most common Python
+LibCST requires Python 3.7+ and can be easily installed using most common Python
 packaging tools. We recommend installing the latest stable release from
 `PyPI <https://pypi.org/project/libcst/>`_ with pip:
 

libcst/_type_enforce.py

@@ -3,17 +3,19 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
-from typing import Any, Iterable, Mapping, MutableMapping, MutableSequence, Tuple
+from typing import (
+    Any,
+    ForwardRef,
+    Iterable,
+    Mapping,
+    MutableMapping,
+    MutableSequence,
+    Tuple,
+)
 
 from typing_extensions import Literal
 from typing_inspect import get_args, get_origin, is_classvar, is_typevar, is_union_type
 
-try:  # py37+
-    from typing import ForwardRef
-except ImportError:  # py36
-    # pyre-fixme[21]: Could not find name `_ForwardRef` in `typing` (stubbed).
-    from typing import _ForwardRef as ForwardRef
-
 
 def is_value_of_type(  # noqa: C901 "too complex"
     # pyre-fixme[2]: Parameter annotation cannot be `Any`.
@@ -47,12 +49,8 @@ def is_value_of_type(  # noqa: C901 "too complex"
     - Type[...]
     """
     if is_classvar(expected_type):
-        # `ClassVar` (no subscript) is implicitly `ClassVar[Any]`
-        if hasattr(expected_type, "__type__"):  # py36
-            expected_type = expected_type.__type__ or Any
-        else:  # py37+
-            classvar_args = get_args(expected_type)
-            expected_type = (classvar_args[0] or Any) if classvar_args else Any
+        classvar_args = get_args(expected_type)
+        expected_type = (classvar_args[0] or Any) if classvar_args else Any
 
     if is_typevar(expected_type):
         # treat this the same as Any
@@ -70,10 +68,7 @@ def is_value_of_type(  # noqa: C901 "too complex"
         )
 
     elif isinstance(expected_origin_type, type(Literal)):
-        if hasattr(expected_type, "__values__"):  # py36
-            literal_values = expected_type.__values__
-        else:  # py37+
-            literal_values = get_args(expected_type, evaluate=True)
+        literal_values = get_args(expected_type, evaluate=True)
         return any(value == literal for literal in literal_values)
 
     elif isinstance(expected_origin_type, ForwardRef):

pyproject.toml

@@ -9,4 +9,4 @@ excludes = ["native/", "stubs/"]
 exclude-modules = '^libcst\.(testing|tests)'
 
 [build-system]
-requires = ["setuptools", "wheel", "setuptools-rust"]
+requires = ["setuptools", "wheel", "setuptools-rust"]

setup.py

@@ -30,7 +30,7 @@ def no_local_scheme(version: str) -> str:
         ),
     },
     name="libcst",
-    description="A concrete syntax tree with AST-like properties for Python 3.5, 3.6, 3.7 and 3.8 programs.",
+    description="A concrete syntax tree with AST-like properties for Python 3.5, 3.6, 3.7, 3.8, 3.9, and 3.10 programs.",
     long_description=long_description,
     long_description_content_type="text/x-rst",
     url="https://github.com/Instagram/LibCST",
@@ -42,7 +42,7 @@ def no_local_scheme(version: str) -> str:
         "libcst.codemod.tests": ["*"],
     },
     test_suite="libcst",
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     setup_requires=["setuptools_scm"],
     install_requires=[dep.strip() for dep in open("requirements.txt").readlines()],
     extras_require={
@@ -62,9 +62,10 @@ def no_local_scheme(version: str) -> str:
     classifiers=[
         "License :: OSI Approved :: MIT License",
         "Topic :: Software Development :: Libraries",
-        "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
     ],
     zip_safe=False,  # for mypy compatibility https://mypy.readthedocs.io/en/latest/installed_packages.html
 )