Skip candidate not providing valid metadata

This is done by catching InstallationError from the underlying
distribution preparation logic. There are three cases to catch:

1. Candidates from indexes. These are simply ignored since we can
   potentially satisfy the requirement with other candidates.
2. Candidates from URLs with a dist name (PEP 508 or #egg=). A new
   UnsatisfiableRequirement class is introduced to represent this; it is
   like an ExplicitRequirement without an underlying candidate. As the
   name suggests, an instance of this can never be satisfied, and will
   cause eventual backtracking.
3. Candidates from URLs without a dist name. This is only possible for
   top-level user requirements, and no recourse is possible for them. So
   we error out eagerly.

The InstallationError raised during distribution preparation is cached
in the factory, like successfully prepared candidates, since we don't
want to repeatedly try to build a candidate if we already know it'd
fail. Plus pip's preparation logic also does not allow packages to be
built multiple times anyway.

8 files changed, 119 insertions, 35 deletions

diff --git a/news/9246.bugfix.rst b/news/9246.bugfix.rst
new file mode 100644
index 000000000..e7ebd398f
--- /dev/null
+++ b/news/9246.bugfix.rst
@@ -0,0 +1,2 @@
+New resolver: Discard a candidate if it fails to provide metadata from source,
+or if the provided metadata is inconsistent, instead of quitting outright.
diff --git a/src/pip/_internal/exceptions.py b/src/pip/_internal/exceptions.py
index 56482caf7..3f2659e87 100644
--- a/src/pip/_internal/exceptions.py
+++ b/src/pip/_internal/exceptions.py
@@ -151,6 +151,21 @@ class MetadataInconsistent(InstallationError):
         )
 
 
+class InstallationSubprocessError(InstallationError):
+    """A subprocess call failed during installation."""
+    def __init__(self, returncode, description):
+        # type: (int, str) -> None
+        self.returncode = returncode
+        self.description = description
+
+    def __str__(self):
+        # type: () -> str
+        return (
+            "Command errored out with exit status {}: {} "
+            "Check the logs for full command output."
+        ).format(self.returncode, self.description)
+
+
 class HashErrors(InstallationError):
     """Multiple HashError instances rolled into one for reporting"""
 
diff --git a/src/pip/_internal/resolution/resolvelib/candidates.py b/src/pip/_internal/resolution/resolvelib/candidates.py
index cd1f18870..5d838d1d4 100644
--- a/src/pip/_internal/resolution/resolvelib/candidates.py
+++ b/src/pip/_internal/resolution/resolvelib/candidates.py
@@ -141,7 +141,7 @@ class _InstallRequirementBackedCandidate(Candidate):
         self._ireq = ireq
         self._name = name
         self._version = version
-        self._dist = None  # type: Optional[Distribution]
+        self.dist = self._prepare()
 
     def __str__(self):
         # type: () -> str
@@ -209,8 +209,6 @@ class _InstallRequirementBackedCandidate(Candidate):
     def _check_metadata_consistency(self, dist):
         # type: (Distribution) -> None
         """Check for consistency of project name and version of dist."""
-        # TODO: (Longer term) Rather than abort, reject this candidate
-        #       and backtrack. This would need resolvelib support.
         name = canonicalize_name(dist.project_name)
         if self._name is not None and self._name != name:
             raise MetadataInconsistent(self._ireq, "name", dist.project_name)
@@ -219,25 +217,14 @@ class _InstallRequirementBackedCandidate(Candidate):
             raise MetadataInconsistent(self._ireq, "version", dist.version)
 
     def _prepare(self):
-        # type: () -> None
-        if self._dist is not None:
-            return
+        # type: () -> Distribution
         try:
             dist = self._prepare_distribution()
         except HashError as e:
             e.req = self._ireq
             raise
-
-        assert dist is not None, "Distribution already installed"
         self._check_metadata_consistency(dist)
-        self._dist = dist
-
-    @property
-    def dist(self):
-        # type: () -> Distribution
-        if self._dist is None:
-            self._prepare()
-        return self._dist
+        return dist
 
     def _get_requires_python_dependency(self):
         # type: () -> Optional[Requirement]
@@ -261,7 +248,6 @@ class _InstallRequirementBackedCandidate(Candidate):
 
     def get_install_requirement(self):
         # type: () -> Optional[InstallRequirement]
-        self._prepare()
         return self._ireq
 
 
diff --git a/src/pip/_internal/resolution/resolvelib/factory.py b/src/pip/_internal/resolution/resolvelib/factory.py
index c723d343b..5cd333bad 100644
--- a/src/pip/_internal/resolution/resolvelib/factory.py
+++ b/src/pip/_internal/resolution/resolvelib/factory.py
@@ -5,6 +5,8 @@ from pip._vendor.packaging.utils import canonicalize_name
 from pip._internal.exceptions import (
     DistributionNotFound,
     InstallationError,
+    InstallationSubprocessError,
+    MetadataInconsistent,
     UnsupportedPythonVersion,
     UnsupportedWheel,
 )
@@ -33,6 +35,7 @@ from .requirements import (
     ExplicitRequirement,
     RequiresPythonRequirement,
     SpecifierRequirement,
+    UnsatisfiableRequirement,
 )
 
 if MYPY_CHECK_RUNNING:
@@ -96,6 +99,7 @@ class Factory(object):
 
         self._link_candidate_cache = {}  # type: Cache[LinkCandidate]
         self._editable_candidate_cache = {}  # type: Cache[EditableCandidate]
+        self._build_failures = {}  # type: Cache[InstallationError]
 
         if not ignore_installed:
             self._installed_dists = {
@@ -130,20 +134,34 @@ class Factory(object):
         name,  # type: Optional[str]
         version,  # type: Optional[_BaseVersion]
     ):
-        # type: (...) -> Candidate
+        # type: (...) -> Optional[Candidate]
         # TODO: Check already installed candidate, and use it if the link and
         # editable flag match.
+        if link in self._build_failures:
+            return None
         if template.editable:
             if link not in self._editable_candidate_cache:
-                self._editable_candidate_cache[link] = EditableCandidate(
-                    link, template, factory=self, name=name, version=version,
-                )
+                try:
+                    self._editable_candidate_cache[link] = EditableCandidate(
+                        link, template, factory=self,
+                        name=name, version=version,
+                    )
+                except (InstallationSubprocessError, MetadataInconsistent) as e:
+                    logger.warning("Discarding %s. %s", link, e)
+                    self._build_failures[link] = e
+                    return None
             base = self._editable_candidate_cache[link]  # type: BaseCandidate
         else:
             if link not in self._link_candidate_cache:
-                self._link_candidate_cache[link] = LinkCandidate(
-                    link, template, factory=self, name=name, version=version,
-                )
+                try:
+                    self._link_candidate_cache[link] = LinkCandidate(
+                        link, template, factory=self,
+                        name=name, version=version,
+                    )
+                except (InstallationSubprocessError, MetadataInconsistent) as e:
+                    logger.warning("Discarding %s. %s", link, e)
+                    self._build_failures[link] = e
+                    return None
             base = self._link_candidate_cache[link]
         if extras:
             return ExtrasCandidate(base, extras)
@@ -204,13 +222,16 @@ class Factory(object):
             for ican in reversed(icans):
                 if not all_yanked and ican.link.is_yanked:
                     continue
-                yield self._make_candidate_from_link(
+                candidate = self._make_candidate_from_link(
                     link=ican.link,
                     extras=extras,
                     template=template,
                     name=name,
                     version=ican.version,
                 )
+                if candidate is None:
+                    continue
+                yield candidate
 
         return FoundCandidates(
             iter_index_candidates,
@@ -274,6 +295,10 @@ class Factory(object):
             name=canonicalize_name(ireq.name) if ireq.name else None,
             version=None,
         )
+        if cand is None:
+            if not ireq.name:
+                raise self._build_failures[ireq.link]
+            return UnsatisfiableRequirement(canonicalize_name(ireq.name))
         return self.make_requirement_from_candidate(cand)
 
     def make_requirement_from_candidate(self, candidate):
diff --git a/src/pip/_internal/resolution/resolvelib/requirements.py b/src/pip/_internal/resolution/resolvelib/requirements.py
index d926d0a06..1229f3537 100644
--- a/src/pip/_internal/resolution/resolvelib/requirements.py
+++ b/src/pip/_internal/resolution/resolvelib/requirements.py
@@ -158,3 +158,44 @@ class RequiresPythonRequirement(Requirement):
         # already implements the prerelease logic, and would have filtered out
         # prerelease candidates if the user does not expect them.
         return self.specifier.contains(candidate.version, prereleases=True)
+
+
+class UnsatisfiableRequirement(Requirement):
+    """A requirement that cannot be satisfied.
+    """
+    def __init__(self, name):
+        # type: (str) -> None
+        self._name = name
+
+    def __str__(self):
+        # type: () -> str
+        return "{} (unavailable)".format(self._name)
+
+    def __repr__(self):
+        # type: () -> str
+        return "{class_name}({name!r})".format(
+            class_name=self.__class__.__name__,
+            name=str(self._name),
+        )
+
+    @property
+    def project_name(self):
+        # type: () -> str
+        return self._name
+
+    @property
+    def name(self):
+        # type: () -> str
+        return self._name
+
+    def format_for_error(self):
+        # type: () -> str
+        return str(self)
+
+    def get_candidate_lookup(self):
+        # type: () -> CandidateLookup
+        return None, None
+
+    def is_satisfied_by(self, candidate):
+        # type: (Candidate) -> bool
+        return False
diff --git a/src/pip/_internal/utils/subprocess.py b/src/pip/_internal/utils/subprocess.py
index 605e711e6..325897c87 100644
--- a/src/pip/_internal/utils/subprocess.py
+++ b/src/pip/_internal/utils/subprocess.py
@@ -7,7 +7,7 @@ import subprocess
 from pip._vendor.six.moves import shlex_quote
 
 from pip._internal.cli.spinners import SpinnerInterface, open_spinner
-from pip._internal.exceptions import InstallationError
+from pip._internal.exceptions import InstallationSubprocessError
 from pip._internal.utils.compat import console_to_str, str_to_display
 from pip._internal.utils.logging import subprocess_logger
 from pip._internal.utils.misc import HiddenText, path_to_display
@@ -233,11 +233,7 @@ def call_subprocess(
                     exit_status=proc.returncode,
                 )
                 subprocess_logger.error(msg)
-            exc_msg = (
-                'Command errored out with exit status {}: {} '
-                'Check the logs for full command output.'
-            ).format(proc.returncode, command_desc)
-            raise InstallationError(exc_msg)
+            raise InstallationSubprocessError(proc.returncode, command_desc)
         elif on_returncode == 'warn':
             subprocess_logger.warning(
                 'Command "%s" had error code %s in %s',
diff --git a/tests/functional/test_new_resolver.py b/tests/functional/test_new_resolver.py
index b730b3cbd..00d82fb95 100644
--- a/tests/functional/test_new_resolver.py
+++ b/tests/functional/test_new_resolver.py
@@ -1218,3 +1218,22 @@ def test_new_resolver_does_not_reinstall_when_from_a_local_index(script):
     assert "Installing collected packages: simple" not in result.stdout, str(result)
     assert "Requirement already satisfied: simple" in result.stdout, str(result)
     assert_installed(script, simple="0.1.0")
+
+
+def test_new_resolver_skip_inconsistent_metadata(script):
+    create_basic_wheel_for_package(script, "A", "1")
+
+    a_2 = create_basic_wheel_for_package(script, "A", "2")
+    a_2.rename(a_2.parent.joinpath("a-3-py2.py3-none-any.whl"))
+
+    result = script.pip(
+        "install",
+        "--no-cache-dir", "--no-index",
+        "--find-links", script.scratch_path,
+        "--verbose",
+        "A",
+        allow_stderr_warning=True,
+    )
+
+    assert " different version in metadata: '2'" in result.stderr, str(result)
+    assert_installed(script, a="1")
diff --git a/tests/unit/test_utils_subprocess.py b/tests/unit/test_utils_subprocess.py
index b0de2bf57..1a0310651 100644
--- a/tests/unit/test_utils_subprocess.py
+++ b/tests/unit/test_utils_subprocess.py
@@ -7,7 +7,7 @@ from textwrap import dedent
 import pytest
 
 from pip._internal.cli.spinners import SpinnerInterface
-from pip._internal.exceptions import InstallationError
+from pip._internal.exceptions import InstallationSubprocessError
 from pip._internal.utils.misc import hide_value
 from pip._internal.utils.subprocess import (
     call_subprocess,
@@ -276,7 +276,7 @@ class TestCallSubprocess(object):
         command = 'print("Hello"); print("world"); exit("fail")'
         args, spinner = self.prepare_call(caplog, log_level, command=command)
 
-        with pytest.raises(InstallationError) as exc:
+        with pytest.raises(InstallationSubprocessError) as exc:
             call_subprocess(args, spinner=spinner)
         result = None
         exc_message = str(exc.value)
@@ -360,7 +360,7 @@ class TestCallSubprocess(object):
             # log level is only WARNING.
             (0, True, None, WARNING, (None, 'done', 2)),
             # Test a non-zero exit status.
-            (3, False, None, INFO, (InstallationError, 'error', 2)),
+            (3, False, None, INFO, (InstallationSubprocessError, 'error', 2)),
             # Test a non-zero exit status also in extra_ok_returncodes.
             (3, False, (3, ), INFO, (None, 'done', 2)),
     ])
@@ -396,7 +396,7 @@ class TestCallSubprocess(object):
         assert spinner.spin_count == expected_spin_count
 
     def test_closes_stdin(self):
-        with pytest.raises(InstallationError):
+        with pytest.raises(InstallationSubprocessError):
             call_subprocess(
                 [sys.executable, '-c', 'input()'],
                 show_stdout=True,