feat(linter): add 'pip check' linter

This linter runs 'pip check' on the venv of the resulting charm and
warns if the virtual environment is inconsistent.

charmcraft/linters.py

@@ -1,4 +1,4 @@
-# Copyright 2021-2022 Canonical Ltd.
+# Copyright 2021-2024 Canonical Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -21,6 +21,8 @@
 import pathlib
 import re
 import shlex
+import subprocess
+import sys
 import typing
 from collections.abc import Generator
 from typing import final
@@ -668,6 +670,49 @@ def run(self, basedir: pathlib.Path) -> str:
         return self._check_additional_files(stage_dir, basedir)
 
 
+class PipCheck(Linter):
+    """Check that the pip virtual environment is valid."""
+
+    name = "pip-check"
+    text = "Virtual environment is valid."
+    url = "https://pip.pypa.io/en/stable/cli/pip_check/"
+
+    def run(self, basedir: pathlib.Path) -> str:
+        """Run pip check."""
+        venv_dir = basedir / "venv"
+        if not venv_dir.is_dir():
+            self.text = "Charm does not contain a Python venv."
+            return self.Result.NONAPPLICABLE
+        python_exe = venv_dir / "bin" / "python"
+        delete_parent = False
+        if not python_exe.parent.exists():
+            delete_parent = True
+            python_exe.parent.mkdir()
+        if not python_exe.exists():
+            delete_python_exe = True
+            python_exe.symlink_to(sys.executable)
+        else:
+            delete_python_exe = False
+
+        pip_cmd = [sys.executable, "-m", "pip", "--python", str(python_exe), "check"]
+        check = subprocess.run(
+            pip_cmd,
+            text=True,
+            capture_output=True,
+        )
+        if check.returncode == 0:
+            result = self.Result.OK
+        else:
+            self.text = check.stdout
+            result = self.Result.WARNING
+        if delete_python_exe:
+            python_exe.unlink()
+        if delete_parent:
+            python_exe.parent.rmdir()
+
+        return result
+
+
 # all checkers to run; the order here is important, as some checkers depend on the
 # results from others
 CHECKERS: list[type[BaseChecker]] = [

pyproject.toml

@@ -29,6 +29,7 @@ dependencies = [
     # https://github.com/msabramo/requests-unixsocket/pull/69
     # When updating, remove the urllib3 constraint from renovate config.
     "urllib3<2.0",
+    "pip>=24.2",
 ]
 classifiers = [
     "Development Status :: 5 - Production/Stable",

tests/integration/test_linters.py

@@ -0,0 +1,60 @@
+# Copyright 2024 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# For further info, check https://github.com/canonical/charmcraft
+"""Unit tests for linters."""
+
+import pathlib
+import subprocess
+import sys
+
+import pytest
+
+from charmcraft import linters
+from charmcraft.models.lint import LintResult
+
+pytestmark = pytest.mark.skipif(sys.platform == "win32", reason="Windows not supported")
+
+
+@pytest.mark.parametrize(
+    "pip_cmd",
+    [
+        ["--version"],
+        ["install", "pytest", "hypothesis"],
+    ]
+)
+def test_pip_check_success(tmp_path: pathlib.Path, pip_cmd: list[str]):
+    venv_path = tmp_path / "venv"
+    subprocess.run([sys.executable, "-m", "venv", venv_path], check=True)
+    subprocess.run([venv_path / "bin" / "python", "-m", "pip", *pip_cmd], check=True)
+
+    lint = linters.PipCheck()
+    assert lint.run(tmp_path) == LintResult.OK
+    assert lint.text == linters.PipCheck.text
+
+
+@pytest.mark.parametrize(
+    "pip_cmd",
+    [
+        ["install", "--no-deps", "pydantic==2.9.2"],
+    ]
+)
+def test_pip_check_failure(tmp_path: pathlib.Path, pip_cmd: list[str]):
+    venv_path = tmp_path / "venv"
+    subprocess.run([sys.executable, "-m", "venv", venv_path], check=True)
+    subprocess.run([venv_path / "bin" / "python", "-m", "pip", *pip_cmd], check=True)
+
+    lint = linters.PipCheck()
+    assert lint.run(tmp_path) == LintResult.WARNING
+    assert "pydantic 2.9.2 requires pydantic-core" in lint.text

tests/unit/test_linters.py

@@ -0,0 +1,54 @@
+# Copyright 2024 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# For further info, check https://github.com/canonical/charmcraft
+"""Unit tests for linters."""
+
+import pathlib
+import subprocess
+import sys
+from charmcraft import linters
+from charmcraft.models.lint import LintResult
+
+
+def test_pip_check_not_venv(fake_path: pathlib.Path):
+    lint = linters.PipCheck()
+    assert lint.run(fake_path) == LintResult.NONAPPLICABLE
+    assert lint.text == "Charm does not contain a Python venv."
+
+
+def test_pip_check_success(fake_path: pathlib.Path, fp):
+    (fake_path / "venv").mkdir()
+    fp.register(
+        [sys.executable, "-m", "pip", "--python", fp.any(), "check"],
+        returncode=0,
+        stdout="Loo loo loo, doing pip stuff. Pip stuff is my favourite stuff."
+    )
+
+    lint = linters.PipCheck()
+    assert lint.run(fake_path) == LintResult.OK
+    assert lint.text == linters.PipCheck.text
+
+
+def test_pip_check_warning(fake_path: pathlib.Path, fp):
+    (fake_path / "venv").mkdir()
+    fp.register(
+        [sys.executable, "-m", "pip", "--python", fp.any(), "check"],
+        returncode=1,
+        stdout="This error was sponsored by Raytheon Knife Missiles™"
+    )
+
+    lint = linters.PipCheck()
+    assert lint.run(fake_path) == LintResult.WARNING
+    assert lint.text == "This error was sponsored by Raytheon Knife Missiles™"