Implement optional per-env lockfiles in tox setup

.flake8

@@ -28,6 +28,12 @@ extend-exclude =
   # Metadata of `pip wheel` cmd is autogenerated
   pip-wheel-metadata,
 
+# IMPORTANT: avoid using ignore option, always use extend-ignore instead
+# Completely and unconditionally ignore the following errors:
+extend-ignore =
+  # Legitimate cases, no need to "fix" these violations:
+  WPS326  # "Found implicit string concatenation" -- nothing bad about this
+
 # https://wemake-python-stylegui.de/en/latest/pages/usage/formatter.html
 #format = wemake
 
@@ -43,6 +49,10 @@ per-file-ignores =
   # and subprocesses (import – S404; call – S603) in tests:
   cheroot/test/test_*.py: S101, S404, S603
 
+  # WPS102 Found incorrect module name pattern
+  # This is not a regular module but a standalone script:
+  bin/pip-wrapper: WPS102
+
   # FIXME:
   cheroot/__init__.py: I003, WPS100, WPS412, WPS420, WPS422, WPS433
   cheroot/__main__.py: WPS130, WPS300

bin/pip-wrapper

@@ -0,0 +1,122 @@
+#! /usr/bin/env python
+"""A pip-wrapper that injects platform-specific constraints into pip."""
+from __future__ import print_function  # noqa: WPS422
+
+import functools
+import os
+import platform
+import subprocess  # noqa: S404
+import sys
+
+print_info = functools.partial(print, file=sys.stderr)
+
+
+def get_runtime_python_tag():
+    """Identify the Python tag of the current runtime.
+
+    :returns: Python tag.
+    """
+    python_minor_ver = sys.version_info[:2]
+    python_implementation = platform.python_implementation()
+
+    if python_implementation == 'PyPy':
+        python_tag_prefix = 'py'
+    else:
+        python_tag_prefix = 'cp'
+
+    # pylint: disable=possibly-unused-variable
+    python_minor_ver_tag = ''.join(map(str, python_minor_ver))
+
+    python_tag = (
+        '{python_tag_prefix!s}{python_minor_ver_tag!s}'.
+        format(**locals())  # noqa: WPS421
+    )
+
+    if python_tag_prefix == 'cp' and python_implementation == 'CPython':
+        print_info(
+            'WARNING: The chosen Python interpreter tag "{python_tag}" '
+            'may not match the current '
+            'Python implementation "{python_implementation}"'.
+            format(**locals()),  # noqa: WPS421
+        )
+
+    return python_tag
+
+
+def get_constraint_file_path(req_dir, toxenv, python_tag):
+    """Identify the constraints filename for the current environment.
+
+    :param req_dir: Requirements directory.
+    :param toxenv: tox testenv.
+    :param python_tag: Python tag.
+
+    :returns: Constraints filename for the current environment.
+    """
+    sys_platform = sys.platform
+    # pylint: disable=possibly-unused-variable
+    platform_machine = platform.machine()
+
+    if toxenv in {'py', 'python'}:
+        toxenv = 'py{ver}'.format(ver=python_tag[2:])
+
+    if sys_platform == 'linux2':
+        sys_platform = 'linux'
+
+    constraint_name = (
+        'tox-{toxenv}-{python_tag}-{sys_platform}-{platform_machine}'.
+        format(**locals())  # noqa: WPS421
+    )
+    return os.path.join(req_dir, os.path.extsep.join((constraint_name, 'txt')))
+
+
+def make_pip_cmd(pip_args, constraint_file_path):
+    """Inject a lockfile constraint into the pip command if present.
+
+    :param pip_args: pip arguments.
+    :param constraint_file_path: Path to a ``constraints.txt``-compatible file.
+
+    :returns: pip command.
+    """
+    pip_cmd = [sys.executable, '-m', 'pip'] + pip_args
+    if os.path.isfile(constraint_file_path):
+        pip_cmd += ['--constraint', constraint_file_path]
+    else:
+        print_info(
+            'WARNING: The expected pinned constraints file for the current env'
+            'does not exist (should be "{constraint_file_path}").'.
+            format(**locals()),  # noqa: WPS421
+        )
+    return pip_cmd
+
+
+def run_cmd(cmd):
+    """Invoke a shell command after logging it.
+
+    :param cmd: The command to invoke.
+    """
+    print_info(
+        'Invoking the following command: {cmd}'.
+        format(cmd=' '.join(cmd)),
+    )
+    subprocess.check_call(cmd)  # noqa: S603
+
+
+def main(argv):
+    """Invoke pip with the matching constraints file, if present.
+
+    :param argv: List of command-line arguments.
+    """
+    constraint_file_path = get_constraint_file_path(
+        req_dir=argv[1],
+        toxenv=argv[0],
+        python_tag=get_runtime_python_tag(),
+    )
+    pip_cmd = make_pip_cmd(
+        pip_args=argv[2:],
+        constraint_file_path=constraint_file_path,
+    )
+    run_cmd(pip_cmd)
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])

requirements/tox-build-dists-cp310-linux-x86_64.in

@@ -0,0 +1 @@
+tox-build-dists.in

requirements/tox-build-dists-cp310-linux-x86_64.txt

@@ -0,0 +1,18 @@
+#
+# This file is autogenerated by pip-compile with python 3.10
+# To update, run:
+#
+#    pip-compile --allow-unsafe --output-file=requirements/tox-build-dists-cp310-linux-x86_64.txt --strip-extras requirements/tox-build-dists-cp310-linux-x86_64.in
+#
+build==0.7.0
+    # via -r requirements/tox-build-dists-cp310-linux-x86_64.in
+packaging==21.3
+    # via build
+pep517==0.12.0
+    # via build
+pyparsing==3.0.6
+    # via packaging
+tomli==2.0.0
+    # via
+    #   build
+    #   pep517

requirements/tox-build-dists-cp39-linux-x86_64.in

@@ -0,0 +1 @@
+tox-build-dists.in

requirements/tox-build-dists-cp39-linux-x86_64.txt

@@ -0,0 +1,18 @@
+#
+# This file is autogenerated by pip-compile with python 3.9
+# To update, run:
+#
+#    pip-compile --allow-unsafe --output-file=requirements/tox-build-dists-cp39-linux-x86_64.txt --strip-extras requirements/tox-build-dists-cp39-linux-x86_64.in
+#
+build==0.7.0
+    # via -r requirements/tox-build-dists-cp39-linux-x86_64.in
+packaging==21.3
+    # via build
+pep517==0.12.0
+    # via build
+pyparsing==3.0.6
+    # via packaging
+tomli==2.0.0
+    # via
+    #   build
+    #   pep517

requirements/tox-build-dists.in

@@ -0,0 +1 @@
+build ~= 0.7.0

requirements/tox-pre-commit-cp310-linux-x86_64.in

@@ -0,0 +1 @@
+tox-pre-commit.in

requirements/tox-pre-commit-cp310-linux-x86_64.txt

@@ -0,0 +1,28 @@
+#
+# This file is autogenerated by pip-compile with python 3.10
+# To update, run:
+#
+#    pip-compile --allow-unsafe --output-file=requirements/tox-pre-commit-cp310-linux-x86_64.txt --strip-extras requirements/tox-pre-commit-cp310-linux-x86_64.in
+#
+cfgv==3.3.1
+    # via pre-commit
+distlib==0.3.4
+    # via virtualenv
+filelock==3.4.2
+    # via virtualenv
+identify==2.4.1
+    # via pre-commit
+nodeenv==1.6.0
+    # via pre-commit
+platformdirs==2.4.1
+    # via virtualenv
+pre-commit==2.16.0
+    # via -r requirements/tox-pre-commit-cp310-linux-x86_64.in
+pyyaml==6.0
+    # via pre-commit
+six==1.16.0
+    # via virtualenv
+toml==0.10.2
+    # via pre-commit
+virtualenv==20.13.0
+    # via pre-commit

requirements/tox-pre-commit-cp39-linux-x86_64.in

@@ -0,0 +1 @@
+tox-pre-commit.in

requirements/tox-pre-commit-cp39-linux-x86_64.txt

@@ -0,0 +1,28 @@
+#
+# This file is autogenerated by pip-compile with python 3.9
+# To update, run:
+#
+#    pip-compile --allow-unsafe --output-file=requirements/tox-pre-commit-cp39-linux-x86_64.txt --strip-extras requirements/tox-pre-commit-cp39-linux-x86_64.in
+#
+cfgv==3.3.1
+    # via pre-commit
+distlib==0.3.4
+    # via virtualenv
+filelock==3.4.2
+    # via virtualenv
+identify==2.4.1
+    # via pre-commit
+nodeenv==1.6.0
+    # via pre-commit
+platformdirs==2.4.1
+    # via virtualenv
+pre-commit==2.16.0
+    # via -r requirements/tox-pre-commit-cp39-linux-x86_64.in
+pyyaml==6.0
+    # via pre-commit
+six==1.16.0
+    # via virtualenv
+toml==0.10.2
+    # via pre-commit
+virtualenv==20.13.0
+    # via pre-commit

requirements/tox-pre-commit.in

@@ -0,0 +1 @@
+pre-commit

requirements/tox-py27-cp27-linux-x86_64.in

@@ -0,0 +1 @@
+tests.in