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.

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.

src/pip/_internal/exceptions.py

@@ -151,6 +151,21 @@ def __str__(self):
         )
 
 
+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"""
 

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

@@ -141,7 +141,7 @@ def __init__(
         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 @@ def _prepare_distribution(self):
     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 @@ def _check_metadata_consistency(self, dist):
             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 @@ def iter_dependencies(self, with_requires):
 
     def get_install_requirement(self):
         # type: () -> Optional[InstallRequirement]
-        self._prepare()
         return self._ireq
 
 

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

@@ -4,7 +4,10 @@
 
 from pip._internal.exceptions import (
     DistributionNotFound,
+    HashError,
     InstallationError,
+    InstallationSubprocessError,
+    MetadataInconsistent,
     UnsupportedPythonVersion,
     UnsupportedWheel,
 )
@@ -33,6 +36,7 @@
     ExplicitRequirement,
     RequiresPythonRequirement,
     SpecifierRequirement,
+    UnsatisfiableRequirement,
 )
 
 if MYPY_CHECK_RUNNING:
@@ -96,6 +100,7 @@ def __init__(
 
         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 +135,34 @@ def _make_candidate_from_link(
         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 +223,16 @@ def iter_index_candidates():
             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 +296,10 @@ def make_requirement_from_install_req(self, ireq, requested_extras):
             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):

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

@@ -158,3 +158,44 @@ def is_satisfied_by(self, candidate):
         # 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

src/pip/_internal/utils/subprocess.py

@@ -7,7 +7,7 @@
 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',

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")