Forward warnings during backend calls to the subprocess logger

src/pip/_internal/distributions/sdist.py

@@ -6,7 +6,10 @@
 from pip._internal.exceptions import InstallationError
 from pip._internal.index.package_finder import PackageFinder
 from pip._internal.metadata import BaseDistribution
-from pip._internal.utils.subprocess import runner_with_spinner_message
+from pip._internal.utils.subprocess import (
+    log_backend_warnings,
+    runner_with_spinner_message,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -87,15 +90,15 @@ def _prepare_build_backend(self, finder: PackageFinder) -> None:
             )
 
     def _get_build_requires_wheel(self) -> Iterable[str]:
-        with self.req.build_env:
+        with self.req.build_env, log_backend_warnings():
             runner = runner_with_spinner_message("Getting requirements to build wheel")
             backend = self.req.pep517_backend
             assert backend is not None
             with backend.subprocess_runner(runner):
                 return backend.get_requires_for_build_wheel()
 
     def _get_build_requires_editable(self) -> Iterable[str]:
-        with self.req.build_env:
+        with self.req.build_env, log_backend_warnings():
             runner = runner_with_spinner_message(
                 "Getting requirements to build editable"
             )

src/pip/_internal/operations/build/metadata.py

@@ -10,7 +10,10 @@
     InstallationSubprocessError,
     MetadataGenerationFailed,
 )
-from pip._internal.utils.subprocess import runner_with_spinner_message
+from pip._internal.utils.subprocess import (
+    log_backend_warnings,
+    runner_with_spinner_message,
+)
 from pip._internal.utils.temp_dir import TempDirectory
 
 
@@ -25,7 +28,7 @@ def generate_metadata(
 
     metadata_dir = metadata_tmpdir.path
 
-    with build_env:
+    with build_env, log_backend_warnings():
         # Note that BuildBackendHookCaller implements a fallback for
         # prepare_metadata_for_build_wheel, so we don't have to
         # consider the possibility that this hook doesn't exist.

src/pip/_internal/operations/build/metadata_editable.py

@@ -10,7 +10,10 @@
     InstallationSubprocessError,
     MetadataGenerationFailed,
 )
-from pip._internal.utils.subprocess import runner_with_spinner_message
+from pip._internal.utils.subprocess import (
+    log_backend_warnings,
+    runner_with_spinner_message,
+)
 from pip._internal.utils.temp_dir import TempDirectory
 
 
@@ -25,7 +28,7 @@ def generate_editable_metadata(
 
     metadata_dir = metadata_tmpdir.path
 
-    with build_env:
+    with build_env, log_backend_warnings():
         # Note that BuildBackendHookCaller implements a fallback for
         # prepare_metadata_for_build_wheel/editable, so we don't have to
         # consider the possibility that this hook doesn't exist.

src/pip/_internal/operations/build/metadata_legacy.py

@@ -12,7 +12,7 @@
     MetadataGenerationFailed,
 )
 from pip._internal.utils.setuptools_build import make_setuptools_egg_info_args
-from pip._internal.utils.subprocess import call_subprocess
+from pip._internal.utils.subprocess import call_subprocess, log_backend_warnings
 from pip._internal.utils.temp_dir import TempDirectory
 
 logger = logging.getLogger(__name__)
@@ -58,7 +58,7 @@ def generate_metadata(
         no_user_config=isolated,
     )
 
-    with build_env:
+    with build_env, log_backend_warnings():
         with open_spinner("Preparing metadata (setup.py)") as spinner:
             try:
                 call_subprocess(

src/pip/_internal/operations/install/editable_legacy.py

@@ -6,7 +6,7 @@
 from pip._internal.build_env import BuildEnvironment
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.setuptools_build import make_setuptools_develop_args
-from pip._internal.utils.subprocess import call_subprocess
+from pip._internal.utils.subprocess import call_subprocess, log_backend_warnings
 
 logger = logging.getLogger(__name__)
 
@@ -38,7 +38,7 @@ def install_editable(
     )
 
     with indent_log():
-        with build_env:
+        with build_env, log_backend_warnings():
             call_subprocess(
                 args,
                 command_desc="python setup.py develop",

src/pip/_internal/req/req_install.py

@@ -53,7 +53,10 @@
     redact_auth_from_url,
 )
 from pip._internal.utils.packaging import safe_extra
-from pip._internal.utils.subprocess import runner_with_spinner_message
+from pip._internal.utils.subprocess import (
+    log_backend_warnings,
+    runner_with_spinner_message,
+)
 from pip._internal.utils.temp_dir import TempDirectory, tempdir_kinds
 from pip._internal.utils.virtualenv import running_under_virtualenv
 from pip._internal.vcs import vcs
@@ -235,7 +238,7 @@ def supports_pyproject_editable(self) -> bool:
         if not self.use_pep517:
             return False
         assert self.pep517_backend
-        with self.build_env:
+        with self.build_env, log_backend_warnings():
             runner = runner_with_spinner_message(
                 "Checking if build backend supports build_editable"
             )

src/pip/_internal/utils/subprocess.py

@@ -1,18 +1,24 @@
+import contextlib
 import logging
 import os
 import shlex
 import subprocess
+import warnings
 from typing import (
     TYPE_CHECKING,
     Any,
     Callable,
+    Generator,
     Iterable,
     List,
     Mapping,
     Optional,
+    TextIO,
+    Type,
     Union,
 )
 
+from pip._vendor.pyproject_hooks import BuildBackendWarning
 from pip._vendor.rich.markup import escape
 
 from pip._internal.cli.spinners import SpinnerInterface, open_spinner
@@ -258,3 +264,24 @@ def runner(
             )
 
     return runner
+
+
+@contextlib.contextmanager
+def log_backend_warnings() -> Generator[None, None, None]:
+    def showwarning(
+        message: Warning | str,
+        category: Type[Warning],
+        filename: str,
+        lineno: int,
+        file: TextIO | None = None,
+        line: str | None = None,
+    ) -> None:
+        if category == BuildBackendWarning:
+            subprocess_logger.warning(message)
+
+    try:
+        original_showwarning = warnings.showwarning
+        warnings.showwarning = showwarning
+        yield
+    finally:
+        warnings.showwarning = original_showwarning

src/pip/_internal/wheel_builder.py

@@ -22,7 +22,7 @@
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.misc import ensure_dir, hash_file
 from pip._internal.utils.setuptools_build import make_setuptools_clean_args
-from pip._internal.utils.subprocess import call_subprocess
+from pip._internal.utils.subprocess import call_subprocess, log_backend_warnings
 from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.utils.urls import path_to_url
 from pip._internal.vcs import vcs
@@ -190,7 +190,7 @@ def _build_one(
         return None
 
     # Install build deps into temporary directory (PEP 518)
-    with req.build_env:
+    with req.build_env, log_backend_warnings():
         wheel_path = _build_one_inside_env(
             req, output_dir, build_options, global_options, editable
         )