Use pyproject-api package (#2274)

Author: gaborbernat

.pre-commit-config.yaml

@@ -21,9 +21,9 @@ repos:
     hooks:
       - id: pyupgrade
         args: ["--py36-plus"]
-        exclude: "^(src/tox/util/pep517/backend.py|tests/demo_pkg_inline/build.py)$"
+        exclude: "^(tests/demo_pkg_inline/build.py)$"
       - id: pyupgrade
-        files: "^(src/tox/util/pep517/backend.py|tests/demo_pkg_inline/build.py)$"
+        files: "^(tests/demo_pkg_inline/build.py)$"
   - repo: https://github.com/pre-commit/pygrep-hooks
     rev: v1.9.0
     hooks:

docs/changelog/2274.feature.rst

@@ -0,0 +1,2 @@
+Moved the python packaging logic into a dedicate package `pyproject-api <https://pypi.org/project/pyproject-api>`_ and
+use it as a dependency - by :user:`gaborbernat`.

setup.cfg

@@ -43,6 +43,7 @@ install_requires =
     packaging>=21
     platformdirs>=2.1
     pluggy>=0.13.1
+    pyproject-api>=0.1
     tomli>=1.1
     virtualenv>=20.6
     importlib-metadata>=4.6.1;python_version<"3.8"

src/tox/execute/pep517_backend.py

@@ -6,12 +6,13 @@
 from types import TracebackType
 from typing import Dict, Optional, Sequence, Tuple, Type
 
+from pyproject_api import BackendFailed
+
 from tox.execute import ExecuteRequest
 from tox.execute.api import Execute, ExecuteInstance, ExecuteOptions, ExecuteStatus
 from tox.execute.local_sub_process import LocalSubProcessExecuteInstance
 from tox.execute.request import StdinSource
 from tox.execute.stream import SyncWrite
-from tox.util.pep517.frontend import BackendFailed
 
 
 class LocalSubProcessPep517Executor(Execute):

src/tox/tox_env/python/virtual_env/package/pep517.py

@@ -7,6 +7,7 @@
 
 from cachetools import cached
 from packaging.requirements import Requirement
+from pyproject_api import BackendFailed, CmdStatus, Frontend
 
 from tox.config.sets import EnvConfigSet
 from tox.execute.api import ExecuteStatus
@@ -19,7 +20,6 @@
 from tox.tox_env.python.package import DevLegacyPackage, PythonPackageToxEnv, SdistPackage, WheelPackage
 from tox.tox_env.register import ToxEnvRegister
 from tox.tox_env.runner import RunToxEnv
-from tox.util.pep517.frontend import BackendFailed, CmdStatus, ConfigSettings, Frontend
 
 from ..api import VirtualEnv
 from .util import dependencies_with_extras
@@ -28,6 +28,7 @@
     from importlib.metadata import Distribution, PathDistribution  # type: ignore[attr-defined]
 else:  # pragma: no cover (<py38)
     from importlib_metadata import Distribution, PathDistribution
+ConfigSettings = Optional[Dict[str, Any]]
 
 
 class ToxBackendFailed(Fail, BackendFailed):