Drop setup.py install support

docs/html/reference/build-system/setup-py.md

@@ -24,8 +24,6 @@ The overall process for building a package is:
 
 - Generate the package's metadata.
 - Generate a wheel for the package.
-  - If this fails and we're trying to install the package, attempt a direct
-    installation.
 
 The wheel can then be used to perform an installation, if necessary.
 
@@ -58,13 +56,6 @@ If this wheel generation fails, pip runs `setup.py clean` to clean up any build
 artifacts that may have been generated. After that, pip will attempt a direct
 installation.
 
-### Direct Installation
-
-When all else fails, pip will invoke `setup.py install` to install a package
-using setuptools' mechanisms to perform the installation. This is currently the
-last-resort fallback for projects that cannot be built into wheels, and may not
-be supported in the future.
-
 ### Editable Installation
 
 For installing packages in "editable" mode

news/8368.removal.rst

@@ -0,0 +1,2 @@
+Remove ``setup.py install`` fallback when building a wheel failed for projects without
+``pyproject.toml``.

src/pip/_internal/commands/install.py

@@ -30,7 +30,6 @@
     check_legacy_setup_py_options,
 )
 from pip._internal.utils.compat import WINDOWS
-from pip._internal.utils.deprecation import LegacyInstallReasonFailedBdistWheel
 from pip._internal.utils.filesystem import test_writable_dir
 from pip._internal.utils.logging import getLogger
 from pip._internal.utils.misc import (
@@ -423,26 +422,14 @@ def run(self, options: Values, args: List[str]) -> int:
                 global_options=global_options,
             )
 
-            # If we're using PEP 517, we cannot do a legacy setup.py install
-            # so we fail here.
-            pep517_build_failure_names: List[str] = [
-                r.name for r in build_failures if r.use_pep517  # type: ignore
-            ]
-            if pep517_build_failure_names:
+            if build_failures:
                 raise InstallationError(
                     "Could not build wheels for {}, which is required to "
                     "install pyproject.toml-based projects".format(
-                        ", ".join(pep517_build_failure_names)
+                        ", ".join(r.name for r in build_failures)  # type: ignore
                     )
                 )
 
-            # For now, we just warn about failures building legacy
-            # requirements, as we'll fall through to a setup.py install for
-            # those.
-            for r in build_failures:
-                if not r.use_pep517:
-                    r.legacy_install_reason = LegacyInstallReasonFailedBdistWheel
-
             to_install = resolver.get_installation_order(requirement_set)
 
             # Check for conflicts in the package set we're installing.

src/pip/_internal/exceptions.py

@@ -361,20 +361,6 @@ def __str__(self) -> str:
         )
 
 
-class LegacyInstallFailure(DiagnosticPipError):
-    """Error occurred while executing `setup.py install`"""
-
-    reference = "legacy-install-failure"
-
-    def __init__(self, package_details: str) -> None:
-        super().__init__(
-            message="Encountered error while trying to install package.",
-            context=package_details,
-            hint_stmt="See above for output from the failure.",
-            note_stmt="This is an issue with the package mentioned above, not pip.",
-        )
-
-
 class InstallationSubprocessError(DiagnosticPipError, InstallationError):
     """A subprocess call failed."""
 

src/pip/_internal/req/req_install.py

@@ -20,7 +20,7 @@
 from pip._vendor.pyproject_hooks import BuildBackendHookCaller
 
 from pip._internal.build_env import BuildEnvironment, NoOpBuildEnvironment
-from pip._internal.exceptions import InstallationError, LegacyInstallFailure
+from pip._internal.exceptions import InstallationError
 from pip._internal.locations import get_scheme
 from pip._internal.metadata import (
     BaseDistribution,
@@ -39,11 +39,10 @@
 from pip._internal.operations.install.editable_legacy import (
     install_editable as install_editable_legacy,
 )
-from pip._internal.operations.install.legacy import install as install_legacy
 from pip._internal.operations.install.wheel import install_wheel
 from pip._internal.pyproject import load_pyproject_toml, make_pyproject_path
 from pip._internal.req.req_uninstall import UninstallPathSet
-from pip._internal.utils.deprecation import LegacyInstallReason, deprecated
+from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.hashes import Hashes
 from pip._internal.utils.misc import (
     ConfiguredBuildBackendHookCaller,
@@ -93,7 +92,6 @@ def __init__(
         self.constraint = constraint
         self.editable = editable
         self.permit_editable_wheels = permit_editable_wheels
-        self.legacy_install_reason: Optional[LegacyInstallReason] = None
 
         # source_dir is the local directory where the linked requirement is
         # located, or unpacked. In case unpacking is needed, creating and
@@ -757,10 +755,9 @@ def install(
             prefix=prefix,
         )
 
-        global_options = global_options if global_options is not None else []
         if self.editable and not self.is_wheel:
             install_editable_legacy(
-                global_options=global_options,
+                global_options=global_options if global_options is not None else [],
                 prefix=prefix,
                 home=home,
                 use_user_site=use_user_site,
@@ -773,66 +770,20 @@ def install(
             self.install_succeeded = True
             return
 
-        if self.is_wheel:
-            assert self.local_file_path
-            install_wheel(
-                self.name,
-                self.local_file_path,
-                scheme=scheme,
-                req_description=str(self.req),
-                pycompile=pycompile,
-                warn_script_location=warn_script_location,
-                direct_url=self.download_info if self.original_link else None,
-                requested=self.user_supplied,
-            )
-            self.install_succeeded = True
-            return
-
-        # TODO: Why don't we do this for editable installs?
-
-        # Extend the list of global options passed on to
-        # the setup.py call with the ones from the requirements file.
-        # Options specified in requirements file override those
-        # specified on the command line, since the last option given
-        # to setup.py is the one that is used.
-        global_options = list(global_options) + self.global_options
-
-        try:
-            if (
-                self.legacy_install_reason is not None
-                and self.legacy_install_reason.emit_before_install
-            ):
-                self.legacy_install_reason.emit_deprecation(self.name)
-            success = install_legacy(
-                global_options=global_options,
-                root=root,
-                home=home,
-                prefix=prefix,
-                use_user_site=use_user_site,
-                pycompile=pycompile,
-                scheme=scheme,
-                setup_py_path=self.setup_py_path,
-                isolated=self.isolated,
-                req_name=self.name,
-                build_env=self.build_env,
-                unpacked_source_directory=self.unpacked_source_directory,
-                req_description=str(self.req),
-            )
-        except LegacyInstallFailure as exc:
-            self.install_succeeded = False
-            raise exc
-        except Exception:
-            self.install_succeeded = True
-            raise
+        assert self.is_wheel
+        assert self.local_file_path
 
-        self.install_succeeded = success
-
-        if (
-            success
-            and self.legacy_install_reason is not None
-            and self.legacy_install_reason.emit_after_success
-        ):
-            self.legacy_install_reason.emit_deprecation(self.name)
+        install_wheel(
+            self.name,
+            self.local_file_path,
+            scheme=scheme,
+            req_description=str(self.req),
+            pycompile=pycompile,
+            warn_script_location=warn_script_location,
+            direct_url=self.download_info if self.original_link else None,
+            requested=self.user_supplied,
+        )
+        self.install_succeeded = True
 
 
 def check_invalid_constraint_type(req: InstallRequirement) -> str:

src/pip/_internal/utils/deprecation.py

@@ -118,44 +118,3 @@ def deprecated(
         raise PipDeprecationWarning(message)
 
     warnings.warn(message, category=PipDeprecationWarning, stacklevel=2)
-
-
-class LegacyInstallReason:
-    def __init__(
-        self,
-        reason: str,
-        replacement: Optional[str] = None,
-        gone_in: Optional[str] = None,
-        feature_flag: Optional[str] = None,
-        issue: Optional[int] = None,
-        emit_after_success: bool = False,
-        emit_before_install: bool = False,
-    ):
-        self._reason = reason
-        self._replacement = replacement
-        self._gone_in = gone_in
-        self._feature_flag = feature_flag
-        self._issue = issue
-        self.emit_after_success = emit_after_success
-        self.emit_before_install = emit_before_install
-
-    def emit_deprecation(self, name: str) -> None:
-        deprecated(
-            reason=self._reason.format(name=name),
-            replacement=self._replacement,
-            gone_in=self._gone_in,
-            feature_flag=self._feature_flag,
-            issue=self._issue,
-        )
-
-
-LegacyInstallReasonFailedBdistWheel = LegacyInstallReason(
-    reason=(
-        "{name} was installed using the legacy 'setup.py install' "
-        "method, because a wheel could not be built for it."
-    ),
-    replacement="to fix the wheel build issue reported above",
-    gone_in="23.1",
-    issue=8368,
-    emit_after_success=True,
-)