Experiemental build env backend by pypa/build

news/11602.feature.rst

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+Add support to use `build <https://pypi.org/project/build/>`_ as an alternative
+isolated build environment implementation. The implementation can be enabled by
+installing ``build`` into the environment, and adding the ``--use-feature=build``
+flag to various pip commands.
+
+``build`` is a light-weight build frontend for ``pyproject.toml`` projects,
+providing various benefits by leveraging modern standards and tools. This
+addition only enables pip to use its logic for environment creation and
+populating build dependencies. Depending on feedback, pip may switch to also
+run the build logic with ``build``, and switch the default build interface in
+the future.

src/pip/_internal/build_env/__init__.py

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+"""Build Environment used for isolation during sdist building.
+
+Three implementations are available:
+
+* NoOpBuildEnvironment: Does not actually do anything, used by legacy code.
+* CustomBuildEnvironment: Old build environment implemented by pip developers.
+* PyPABuildEnvironment: New build environment that uses pypa/build.
+"""
+
+from .base import NoOpBuildEnvironment, get_runnable_pip
+from .custom import BuildEnvironment as CustomBuildEnvironment
+from .pypa import BuildEnvironment as PyPABuildEnvironment
+
+BuildEnvironment = NoOpBuildEnvironment
+
+__all__ = [
+    "BuildEnvironment",
+    "CustomBuildEnvironment",
+    "NoOpBuildEnvironment",
+    "PyPABuildEnvironment",
+    "get_runnable_pip",
+]