mypy 1 and 2 Support

.github/actions/pysen-test-post-313/action.yml

@@ -8,4 +8,4 @@ runs:
     - '-c'
     # Changing the ownership is required. See the following link for more details:
     # https://github.blog/2022-04-12-git-security-vulnerability-announced/
-    - "chown -R $(id -u):$(id -g) . && tox --parallel -e 'py{313,314}-post313'"
+    - "chown -R $(id -u):$(id -g) . && tox --parallel -e 'py{313,314}-post313, py{313,314}-mypy2'"

pyproject.toml

@@ -37,7 +37,7 @@ lint = [
   "flake8>=3.7,<5",
   "flake8-bugbear",  # flake8 doesn't have a dependency for bugbear plugin
   "isort>=4.3,<5.2.0",
-  "mypy>=0.770,<0.800",
+  "mypy>=0.770,<3",
 ]
 
 [project.scripts]

src/pysen/ext/mypy_wrapper.py

@@ -8,7 +8,7 @@
 from pysen.command import check_command_installed
 from pysen.dist_version import get_version
 from pysen.error_lines import parse_error_lines
-from pysen.exceptions import IncompatibleVersionError
+from pysen.exceptions import IncompatibleVersionError, PysenError
 from pysen.path import PathLikeType, change_dir, get_relative_path, resolve_path
 from pysen.py_version import PythonVersion
 from pysen.reporter import Reporter
@@ -191,11 +191,25 @@ class MypyTarget:
 @functools.lru_cache(1)
 def _check_mypy_version() -> None:
     version = get_version("mypy")
-    if version.major >= 2 or version.major == 0 and version.minor < 770:
+    if version.major >= 3 or version.major == 0 and version.minor < 770:
         raise IncompatibleVersionError(
-            f"pysen only supports mypy version >=0.770, <2. "
+            f"pysen only supports mypy version >=0.770, <3. "
             f"version {version} is not supported."
         )
+    if version.major >= 2:
+        # mypy >=2 uses a sqlite-backed cache by default, which requires the
+        # stdlib sqlite3 module (and the underlying libsqlite3 shared library)
+        # to be importable. Fail early with an actionable message instead of
+        # letting mypy crash with an INTERNAL ERROR.
+        try:
+            import sqlite3  # noqa: F401
+        except ImportError as e:
+            raise PysenError(
+                f"mypy {version} requires the sqlite3 module for its cache, "
+                f"but it could not be imported ({e}). Please install sqlite "
+                f"(e.g. the libsqlite3 / sqlite-libs system package) and "
+                f"rebuild Python with sqlite3 support."
+            ) from e
 
 
 def run(

tests/test_mypy_wrapper.py

@@ -1,8 +1,11 @@
 import pathlib
+import sys
+from unittest import mock
 
 import pytest
 
-from pysen.ext.mypy_wrapper import MypyPlugin, MypyTarget, run
+from pysen.exceptions import IncompatibleVersionError, PysenError
+from pysen.ext.mypy_wrapper import MypyPlugin, MypyTarget, _check_mypy_version, run
 from pysen.reporter import Reporter
 
 BASE_DIR = pathlib.Path(__file__).resolve().parent
@@ -13,6 +16,51 @@ def test_run_zero_source() -> None:
     assert run(reporter, BASE_DIR, BASE_DIR, MypyTarget([]), True) == 0
 
 
+def test__check_mypy_version() -> None:
+    def check(version: str) -> None:
+        _check_mypy_version.cache_clear()
+        with mock.patch(
+            "pysen.dist_version.distribution",
+            return_value=mock.Mock(version=version),
+        ):
+            # decouple the version-logic check from the host's sqlite3
+            # availability; the sqlite3 requirement for mypy >=2 is covered by
+            # test__check_mypy_version_requires_sqlite_for_mypy2
+            with mock.patch.dict(sys.modules, {"sqlite3": mock.Mock()}):
+                _check_mypy_version()
+
+    # supported: >=0.770, <3
+    check("0.770")
+    check("0.991")
+    check("1.19.0")
+    check("2.0.0")
+    check("2.1.0")
+
+    # unsupported
+    for version in ("0.760", "3.0.0"):
+        with pytest.raises(IncompatibleVersionError):
+            check(version)
+
+
+def test__check_mypy_version_requires_sqlite_for_mypy2() -> None:
+    def check(version: str) -> None:
+        _check_mypy_version.cache_clear()
+        with mock.patch(
+            "pysen.dist_version.distribution",
+            return_value=mock.Mock(version=version),
+        ):
+            # setting the entry to None makes `import sqlite3` raise ImportError
+            with mock.patch.dict(sys.modules, {"sqlite3": None}):
+                _check_mypy_version()
+
+    # mypy >=2 requires sqlite3
+    with pytest.raises(PysenError, match="sqlite3"):
+        check("2.0.0")
+
+    # mypy <2 does not need sqlite3
+    check("1.19.0")
+
+
 def test_mypy_plugin() -> None:
     script_plugin = MypyPlugin(script=pathlib.Path("/foo/bar/baz"))
     script_plugin2 = MypyPlugin(script=pathlib.Path("./bar/baz"))

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{310}-dacite150-isort51-black{20,22}-mypy078, py{311,312}-dacite150-isort51-black22-mypy099, development, latest, py{313,314}-post313
+envlist = py{310}-dacite150-isort51-black{20,22}-mypy078, py{311,312}-dacite150-isort51-black22-mypy099, development, latest, py{313,314}-post313, py{313,314}-mypy2
 isolated_build = True
 
 [testenv]
@@ -26,7 +26,14 @@ setenv =
 basepython = python3.10
 deps =
     pipenv==2022.9.8
+    # pipenv 2022.9.8 imports pkg_resources, which was removed in setuptools
+    # >=81; current virtualenv seeds a newer setuptools, so pin it back.
+    setuptools<81
 extras = lint
+setenv =
+    LANG = C
+    # isolate pipenv's cache per env; the shared default races under --parallel
+    PIPENV_CACHE_DIR = {envdir}/.pipenv-cache
 commands =
     pipenv sync --system
     pip install .
@@ -37,7 +44,14 @@ commands =
 basepython = python3.10
 deps =
     pipenv==2022.9.8
+    # pipenv 2022.9.8 imports pkg_resources, which was removed in setuptools
+    # >=81; current virtualenv seeds a newer setuptools, so pin it back.
+    setuptools<81
 extras = lint
+setenv =
+    LANG = C
+    # isolate pipenv's cache per env; the shared default races under --parallel
+    PIPENV_CACHE_DIR = {envdir}/.pipenv-cache
 commands =
     pipenv sync --system
     pip install .
@@ -57,3 +71,17 @@ changedir = version_testing/post_313
 commands =
     pip install ../../
     pysen run lint
+
+[testenv:py{313,314}-mypy2]
+deps =
+    pipenv==2026.0.2
+    mypy>=2.0,<3
+    isort==7.0.0
+    black==25.12.0
+    flake8==7.3.0
+    flake8-bugbear==25.11.29
+    importlib-metadata==8.7.0
+changedir = version_testing/post_mypy2
+commands =
+    pip install ../../
+    pysen run lint

version_testing/README.md

@@ -3,4 +3,20 @@
 ```bash
 $ docker build -t quay.io/pysen/pysen-test .
 $ docker push quay.io/pysen/pysen-test
-```
+```
+
+## Directories
+
+- `post_310` / `post_313`: smoke-test projects exercised by the corresponding
+  `tox` environments for newer Python interpreters.
+- `post_mypy2`: smoke-test project for `mypy >=2` (`py{313,314}-mypy2` tox env).
+
+### Note on mypy >=2 and `py_version`
+
+mypy `>=2` only supports type-checking against `python_version >= 3.10`. When a
+pysen config sets an older `py_version` (e.g. `py27`, `py38`, `py39`), pysen
+still emits `python_version = 3.x` into the mypy config. mypy `>=2` prints a
+warning (`python_version: Python 3.8 is not supported (must be 3.10 or higher)`)
+and silently falls back to its minimum supported version, so the effective
+type-checking semantics differ from what the user requested. The `post_mypy2`
+example therefore uses `py_version = "py313"`.

version_testing/post_313/Dockerfile

@@ -3,6 +3,8 @@ FROM alpine:3.23
 COPY --from=python:3.13.11-alpine3.23 /usr/local/ /usr/local/
 COPY --from=python:3.14.2-alpine3.23 /usr/local/ /usr/local/
 
-RUN apk add --no-cache bash git \
+# sqlite-libs is required by mypy >=2, whose default cache backend uses sqlite3
+# (mypy <2 used a filesystem metastore and did not need it).
+RUN apk add --no-cache bash git sqlite-libs \
     && pip3.14 install --no-cache-dir tox==3.28.0
 ENV TOX_PARALLEL_NO_SPINNER=1

version_testing/post_mypy2/pyproject.toml

@@ -0,0 +1,20 @@
+[project]
+name = "example_post_mypy2"
+requires-python = ">=3.13"
+description = "example project for mypy version >=2"
+
+[tool.pysen]
+version = "0.12"
+
+[tool.pysen.lint]
+enable_black = true
+enable_flake8 = true
+enable_isort = true
+enable_mypy = true
+mypy_preset = "very_strict"
+# NOTE: mypy >=2 only supports checking python_version >=3.10. Older py_version
+# values (py27/py38/py39) are rejected by mypy and silently fall back to its
+# minimum supported version. See version_testing/README.md.
+py_version = "py313"
+[[tool.pysen.lint.mypy_targets]]
+  paths = ["src"]

version_testing/post_mypy2/src/example_code.py

@@ -0,0 +1,2 @@
+def main(arg1: str, arg2: int) -> bool:
+    return arg1.isdigit() and arg2 > 0