refactor: Add BuildEnvironmentInstaller protocol

src/pip/_internal/build_env.py

@@ -11,7 +11,7 @@
 from collections import OrderedDict
 from collections.abc import Iterable
 from types import TracebackType
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Protocol
 
 from pip._vendor.packaging.version import Version
 
@@ -26,6 +26,7 @@
 
 if TYPE_CHECKING:
     from pip._internal.index.package_finder import PackageFinder
+    from pip._internal.req.req_install import InstallRequirement
 
 logger = logging.getLogger(__name__)
 
@@ -79,10 +80,108 @@ def _get_system_sitepackages() -> set[str]:
     return {os.path.normcase(path) for path in system_sites}
 
 
+class BuildEnvironmentInstaller(Protocol):
+    """
+    Interface for installing build dependencies into an isolated build
+    environment.
+    """
+
+    def install(
+        self,
+        requirements: Iterable[str],
+        prefix: _Prefix,
+        *,
+        kind: str,
+        for_req: InstallRequirement | None,
+    ) -> None: ...
+
+
+class SubprocessBuildEnvironmentInstaller:
+    """
+    Install build dependencies by calling pip in a subprocess.
+    """
+
+    def __init__(self, finder: PackageFinder) -> None:
+        self.finder = finder
+
+    def install(
+        self,
+        requirements: Iterable[str],
+        prefix: _Prefix,
+        *,
+        kind: str,
+        for_req: InstallRequirement | None,
+    ) -> None:
+        finder = self.finder
+        args: list[str] = [
+            sys.executable,
+            get_runnable_pip(),
+            "install",
+            "--ignore-installed",
+            "--no-user",
+            "--prefix",
+            prefix.path,
+            "--no-warn-script-location",
+            "--disable-pip-version-check",
+            # As the build environment is ephemeral, it's wasteful to
+            # pre-compile everything, especially as not every Python
+            # module will be used/compiled in most cases.
+            "--no-compile",
+            # The prefix specified two lines above, thus
+            # target from config file or env var should be ignored
+            "--target",
+            "",
+        ]
+        if logger.getEffectiveLevel() <= logging.DEBUG:
+            args.append("-vv")
+        elif logger.getEffectiveLevel() <= VERBOSE:
+            args.append("-v")
+        for format_control in ("no_binary", "only_binary"):
+            formats = getattr(finder.format_control, format_control)
+            args.extend(
+                (
+                    "--" + format_control.replace("_", "-"),
+                    ",".join(sorted(formats or {":none:"})),
+                )
+            )
+
+        index_urls = finder.index_urls
+        if index_urls:
+            args.extend(["-i", index_urls[0]])
+            for extra_index in index_urls[1:]:
+                args.extend(["--extra-index-url", extra_index])
+        else:
+            args.append("--no-index")
+        for link in finder.find_links:
+            args.extend(["--find-links", link])
+
+        if finder.proxy:
+            args.extend(["--proxy", finder.proxy])
+        for host in finder.trusted_hosts:
+            args.extend(["--trusted-host", host])
+        if finder.custom_cert:
+            args.extend(["--cert", finder.custom_cert])
+        if finder.client_cert:
+            args.extend(["--client-cert", finder.client_cert])
+        if finder.allow_all_prereleases:
+            args.append("--pre")
+        if finder.prefer_binary:
+            args.append("--prefer-binary")
+        args.append("--")
+        args.extend(requirements)
+        with open_spinner(f"Installing {kind}") as spinner:
+            call_subprocess(
+                args,
+                command_desc=f"pip subprocess to install {kind}",
+                spinner=spinner,
+            )
+
+
 class BuildEnvironment:
     """Creates and manages an isolated environment to install build deps"""
 
-    def __init__(self) -> None:
+    def __init__(self, installer: BuildEnvironmentInstaller) -> None:
+        self.installer = installer
         temp_dir = TempDirectory(kind=tempdir_kinds.BUILD_ENV, globally_managed=True)
 
         self._prefixes = OrderedDict(
@@ -205,96 +304,18 @@ def check_requirements(
 
     def install_requirements(
         self,
-        finder: PackageFinder,
         requirements: Iterable[str],
         prefix_as_string: str,
         *,
         kind: str,
+        for_req: InstallRequirement | None = None,
     ) -> None:
         prefix = self._prefixes[prefix_as_string]
         assert not prefix.setup
         prefix.setup = True
         if not requirements:
             return
-        self._install_requirements(
-            get_runnable_pip(),
-            finder,
-            requirements,
-            prefix,
-            kind=kind,
-        )
-
-    @staticmethod
-    def _install_requirements(
-        pip_runnable: str,
-        finder: PackageFinder,
-        requirements: Iterable[str],
-        prefix: _Prefix,
-        *,
-        kind: str,
-    ) -> None:
-        args: list[str] = [
-            sys.executable,
-            pip_runnable,
-            "install",
-            "--ignore-installed",
-            "--no-user",
-            "--prefix",
-            prefix.path,
-            "--no-warn-script-location",
-            "--disable-pip-version-check",
-            # As the build environment is ephemeral, it's wasteful to
-            # pre-compile everything, especially as not every Python
-            # module will be used/compiled in most cases.
-            "--no-compile",
-            # The prefix specified two lines above, thus
-            # target from config file or env var should be ignored
-            "--target",
-            "",
-        ]
-        if logger.getEffectiveLevel() <= logging.DEBUG:
-            args.append("-vv")
-        elif logger.getEffectiveLevel() <= VERBOSE:
-            args.append("-v")
-        for format_control in ("no_binary", "only_binary"):
-            formats = getattr(finder.format_control, format_control)
-            args.extend(
-                (
-                    "--" + format_control.replace("_", "-"),
-                    ",".join(sorted(formats or {":none:"})),
-                )
-            )
-
-        index_urls = finder.index_urls
-        if index_urls:
-            args.extend(["-i", index_urls[0]])
-            for extra_index in index_urls[1:]:
-                args.extend(["--extra-index-url", extra_index])
-        else:
-            args.append("--no-index")
-        for link in finder.find_links:
-            args.extend(["--find-links", link])
-
-        if finder.proxy:
-            args.extend(["--proxy", finder.proxy])
-        for host in finder.trusted_hosts:
-            args.extend(["--trusted-host", host])
-        if finder.custom_cert:
-            args.extend(["--cert", finder.custom_cert])
-        if finder.client_cert:
-            args.extend(["--client-cert", finder.client_cert])
-        if finder.allow_all_prereleases:
-            args.append("--pre")
-        if finder.prefer_binary:
-            args.append("--prefer-binary")
-        args.append("--")
-        args.extend(requirements)
-        with open_spinner(f"Installing {kind}") as spinner:
-            call_subprocess(
-                args,
-                command_desc=f"pip subprocess to install {kind}",
-                spinner=spinner,
-            )
+        self.installer.install(requirements, prefix, kind=kind, for_req=for_req)
 
 
 class NoOpBuildEnvironment(BuildEnvironment):
@@ -319,10 +340,10 @@ def cleanup(self) -> None:
 
     def install_requirements(
         self,
-        finder: PackageFinder,
         requirements: Iterable[str],
         prefix_as_string: str,
         *,
         kind: str,
+        for_req: InstallRequirement | None = None,
     ) -> None:
         raise NotImplementedError()

src/pip/_internal/cli/req_command.py

@@ -12,6 +12,7 @@
 from optparse import Values
 from typing import Any
 
+from pip._internal.build_env import SubprocessBuildEnvironmentInstaller
 from pip._internal.cache import WheelCache
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.index_command import IndexGroupCommand
@@ -136,6 +137,7 @@ def make_requirement_preparer(
             src_dir=options.src_dir,
             download_dir=download_dir,
             build_isolation=options.build_isolation,
+            build_isolation_installer=SubprocessBuildEnvironmentInstaller(finder),
             check_build_deps=options.check_build_deps,
             build_tracker=build_tracker,
             session=session,

src/pip/_internal/distributions/base.py

@@ -7,7 +7,7 @@
 from pip._internal.req import InstallRequirement
 
 if TYPE_CHECKING:
-    from pip._internal.index.package_finder import PackageFinder
+    from pip._internal.build_env import BuildEnvironmentInstaller
 
 
 class AbstractDistribution(metaclass=abc.ABCMeta):
@@ -48,7 +48,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
     @abc.abstractmethod
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        build_env_installer: BuildEnvironmentInstaller,
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None:

src/pip/_internal/distributions/installed.py

@@ -1,9 +1,13 @@
 from __future__ import annotations
 
+from typing import TYPE_CHECKING
+
 from pip._internal.distributions.base import AbstractDistribution
-from pip._internal.index.package_finder import PackageFinder
 from pip._internal.metadata import BaseDistribution
 
+if TYPE_CHECKING:
+    from pip._internal.build_env import BuildEnvironmentInstaller
+
 
 class InstalledDistribution(AbstractDistribution):
     """Represents an installed package.
@@ -22,7 +26,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
 
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        build_env_installer: BuildEnvironmentInstaller,
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None:

src/pip/_internal/distributions/sdist.py

@@ -11,7 +11,7 @@
 from pip._internal.utils.subprocess import runner_with_spinner_message
 
 if TYPE_CHECKING:
-    from pip._internal.index.package_finder import PackageFinder
+    from pip._internal.build_env import BuildEnvironmentInstaller
 
 logger = logging.getLogger(__name__)
 
@@ -34,7 +34,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
 
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        build_env_installer: BuildEnvironmentInstaller,
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None:
@@ -46,7 +46,7 @@ def prepare_distribution_metadata(
         if should_isolate:
             # Setup an isolated environment and install the build backend static
             # requirements in it.
-            self._prepare_build_backend(finder)
+            self._prepare_build_backend(build_env_installer)
             # Check that if the requirement is editable, it either supports PEP 660 or
             # has a setup.py or a setup.cfg. This cannot be done earlier because we need
             # to setup the build backend to verify it supports build_editable, nor can
@@ -56,7 +56,7 @@ def prepare_distribution_metadata(
             # without setup.py nor setup.cfg.
             self.req.isolated_editable_sanity_check()
             # Install the dynamic build requirements.
-            self._install_build_reqs(finder)
+            self._install_build_reqs(build_env_installer)
         # Check if the current environment provides build dependencies
         should_check_deps = self.req.use_pep517 and check_build_deps
         if should_check_deps:
@@ -71,15 +71,17 @@ def prepare_distribution_metadata(
                 self._raise_missing_reqs(missing)
         self.req.prepare_metadata()
 
-    def _prepare_build_backend(self, finder: PackageFinder) -> None:
+    def _prepare_build_backend(
+        self, build_env_installer: BuildEnvironmentInstaller
+    ) -> None:
         # Isolate in a BuildEnvironment and install the build-time
         # requirements.
         pyproject_requires = self.req.pyproject_requires
         assert pyproject_requires is not None
 
-        self.req.build_env = BuildEnvironment()
+        self.req.build_env = BuildEnvironment(build_env_installer)
         self.req.build_env.install_requirements(
-            finder, pyproject_requires, "overlay", kind="build dependencies"
+            pyproject_requires, "overlay", kind="build dependencies", for_req=self.req
         )
         conflicting, missing = self.req.build_env.check_requirements(
             self.req.requirements_to_check
@@ -115,7 +117,9 @@ def _get_build_requires_editable(self) -> Iterable[str]:
             with backend.subprocess_runner(runner):
                 return backend.get_requires_for_build_editable()
 
-    def _install_build_reqs(self, finder: PackageFinder) -> None:
+    def _install_build_reqs(
+        self, build_env_installer: BuildEnvironmentInstaller
+    ) -> None:
         # Install any extra build dependencies that the backend requests.
         # This must be done in a second pass, as the pyproject.toml
         # dependencies must be installed before we can call the backend.
@@ -131,7 +135,7 @@ def _install_build_reqs(self, finder: PackageFinder) -> None:
         if conflicting:
             self._raise_conflicts("the backend dependencies", conflicting)
         self.req.build_env.install_requirements(
-            finder, missing, "normal", kind="backend dependencies"
+            missing, "normal", kind="backend dependencies", for_req=self.req
         )
 
     def _raise_conflicts(

src/pip/_internal/distributions/wheel.py

@@ -12,7 +12,7 @@
 )
 
 if TYPE_CHECKING:
-    from pip._internal.index.package_finder import PackageFinder
+    from pip._internal.build_env import BuildEnvironmentInstaller
 
 
 class WheelDistribution(AbstractDistribution):
@@ -37,7 +37,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
 
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        build_env_installer: BuildEnvironmentInstaller,
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None: