Add --use-deprecated=backtrack-on-build-failures

This serves as an opt-out from build failures causing the entire
installation to abort.

src/pip/_internal/cli/cmdoptions.py

@@ -964,7 +964,7 @@ use_deprecated_feature: Callable[..., Option] = partial(
     metavar="feature",
     action="append",
     default=[],
-    choices=["legacy-resolver", "out-of-tree-build"],
+    choices=["legacy-resolver", "out-of-tree-build", "backtrack-on-build-failures"],
     help=("Enable deprecated functionality, that will be removed in the future."),
 )
 

src/pip/_internal/cli/req_command.py

@@ -227,6 +227,31 @@ class RequirementCommand(IndexGroupCommand):
 
         return "2020-resolver"
 
+    @staticmethod
+    def determine_build_failure_suppression(options: Values) -> bool:
+        """Determines whether build failures should be suppressed and backtracked on."""
+        if "backtrack-on-build-failures" not in options.deprecated_features_enabled:
+            return False
+
+        if "legacy-resolver" in options.deprecated_features_enabled:
+            raise CommandError("Cannot backtrack with legacy resolver.")
+
+        deprecated(
+            reason=(
+                "Backtracking on build failures can mask issues related to how "
+                "a package generates metadata or builds a wheel. This flag will "
+                "be removed in pip 22.2."
+            ),
+            gone_in=None,
+            replacement=(
+                "avoiding known-bad versions by explicitly telling pip to ignore them "
+                "(either directly as requirements, or via a constraints file)"
+            ),
+            feature_flag=None,
+            issue=10655,
+        )
+        return True
+
     @classmethod
     def make_requirement_preparer(
         cls,
@@ -323,6 +348,7 @@ class RequirementCommand(IndexGroupCommand):
             isolated=options.isolated_mode,
             use_pep517=use_pep517,
         )
+        suppress_build_failures = cls.determine_build_failure_suppression(options)
         resolver_variant = cls.determine_resolver_variant(options)
         # The long import name and duplicated invocation is needed to convince
         # Mypy into correctly typechecking. Otherwise it would complain the
@@ -342,6 +368,7 @@ class RequirementCommand(IndexGroupCommand):
                 force_reinstall=force_reinstall,
                 upgrade_strategy=upgrade_strategy,
                 py_version_info=py_version_info,
+                suppress_build_failures=suppress_build_failures,
             )
         import pip._internal.resolution.legacy.resolver
 

src/pip/_internal/resolution/resolvelib/factory.py

@@ -27,6 +27,7 @@ from pip._internal.cache import CacheEntry, WheelCache
 from pip._internal.exceptions import (
     DistributionNotFound,
     InstallationError,
+    InstallationSubprocessError,
     MetadataInconsistent,
     UnsupportedPythonVersion,
     UnsupportedWheel,
@@ -96,6 +97,7 @@ class Factory:
         force_reinstall: bool,
         ignore_installed: bool,
         ignore_requires_python: bool,
+        suppress_build_failures: bool,
         py_version_info: Optional[Tuple[int, ...]] = None,
     ) -> None:
         self._finder = finder
@@ -106,6 +108,7 @@ class Factory:
         self._use_user_site = use_user_site
         self._force_reinstall = force_reinstall
         self._ignore_requires_python = ignore_requires_python
+        self._suppress_build_failures = suppress_build_failures
 
         self._build_failures: Cache[InstallationError] = {}
         self._link_candidate_cache: Cache[LinkCandidate] = {}
@@ -198,6 +201,13 @@ class Factory:
                     )
                     self._build_failures[link] = e
                     return None
+                except InstallationSubprocessError as e:
+                    if not self._suppress_build_failures:
+                        raise
+                    logger.warning("Discarding %s due to build failure: %s", link, e)
+                    self._build_failures[link] = e
+                    return None
+
             base: BaseCandidate = self._editable_candidate_cache[link]
         else:
             if link not in self._link_candidate_cache:
@@ -218,6 +228,12 @@ class Factory:
                     )
                     self._build_failures[link] = e
                     return None
+                except InstallationSubprocessError as e:
+                    if not self._suppress_build_failures:
+                        raise
+                    logger.warning("Discarding %s due to build failure: %s", link, e)
+                    self._build_failures[link] = e
+                    return None
             base = self._link_candidate_cache[link]
 
         if not extras:

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -47,6 +47,7 @@ class Resolver(BaseResolver):
         ignore_requires_python: bool,
         force_reinstall: bool,
         upgrade_strategy: str,
+        suppress_build_failures: bool,
         py_version_info: Optional[Tuple[int, ...]] = None,
     ):
         super().__init__()
@@ -61,6 +62,7 @@ class Resolver(BaseResolver):
             force_reinstall=force_reinstall,
             ignore_installed=ignore_installed,
             ignore_requires_python=ignore_requires_python,
+            suppress_build_failures=suppress_build_failures,
             py_version_info=py_version_info,
         )
         self.ignore_dependencies = ignore_dependencies

tests/functional/test_new_resolver.py

@@ -2329,6 +2329,26 @@ def test_new_resolver_do_not_backtrack_on_build_failure(
     assert "egg_info" in result.stderr
 
 
+def test_new_resolver_flag_permits_backtracking_on_build_failure(
+    script: PipTestEnvironment,
+) -> None:
+    create_basic_sdist_for_package(script, "pkg1", "2.0", fails_egg_info=True)
+    create_basic_wheel_for_package(script, "pkg1", "1.0")
+
+    script.pip(
+        "install",
+        "--use-deprecated=backtrack-on-build-failures",
+        "--no-cache-dir",
+        "--no-index",
+        "--find-links",
+        script.scratch_path,
+        "pkg1",
+        allow_stderr_warning=True,
+    )
+
+    script.assert_installed(pkg1="1.0")
+
+
 def test_new_resolver_works_when_failing_package_builds_are_disallowed(
     script: PipTestEnvironment,
 ) -> None:

tests/unit/resolution_resolvelib/conftest.py

@@ -63,6 +63,7 @@ def factory(finder: PackageFinder, preparer: RequirementPreparer) -> Iterator[Fa
         force_reinstall=False,
         ignore_installed=False,
         ignore_requires_python=False,
+        suppress_build_failures=False,
         py_version_info=None,
     )
 

tests/unit/resolution_resolvelib/test_resolver.py

@@ -29,6 +29,7 @@ def resolver(preparer: RequirementPreparer, finder: PackageFinder) -> Resolver:
         ignore_requires_python=False,
         force_reinstall=False,
         upgrade_strategy="to-satisfy-only",
+        suppress_build_failures=False,
     )
     return resolver