Straighten up extra comps across metadata backends

The importlib.metadata and pkg_resources backends unfortunately
normalize extras differently, and we don't really want to continue using
the latter's logic (being partially lossy while still not compliant to
standards), so we add a new abstraction for the purpose.

src/pip/_internal/metadata/__init__.py

@@ -9,7 +9,7 @@
 from .base import BaseDistribution, BaseEnvironment, FilesystemWheel, MemoryWheel, Wheel
 
 if TYPE_CHECKING:
-    from typing import Protocol
+    from typing import Literal, Protocol
 else:
     Protocol = object
 
@@ -50,6 +50,7 @@ def _should_use_importlib_metadata() -> bool:
 
 
 class Backend(Protocol):
+    NAME: 'Literal["importlib", "pkg_resources"]'
     Distribution: Type[BaseDistribution]
     Environment: Type[BaseEnvironment]
 

src/pip/_internal/metadata/base.py

@@ -24,7 +24,7 @@
 
 from pip._vendor.packaging.requirements import Requirement
 from pip._vendor.packaging.specifiers import InvalidSpecifier, SpecifierSet
-from pip._vendor.packaging.utils import NormalizedName
+from pip._vendor.packaging.utils import NormalizedName, canonicalize_name
 from pip._vendor.packaging.version import LegacyVersion, Version
 
 from pip._internal.exceptions import NoneMetadataError
@@ -37,7 +37,6 @@
 from pip._internal.utils.compat import stdlib_pkgs  # TODO: Move definition here.
 from pip._internal.utils.egg_link import egg_link_path_from_sys_path
 from pip._internal.utils.misc import is_local, normalize_path
-from pip._internal.utils.packaging import safe_extra
 from pip._internal.utils.urls import url_to_path
 
 from ._json import msg_to_json
@@ -460,6 +459,19 @@ def iter_provided_extras(self) -> Iterable[str]:
 
         For modern .dist-info distributions, this is the collection of
         "Provides-Extra:" entries in distribution metadata.
+
+        The return value of this function is not particularly useful other than
+        display purposes due to backward compatibility issues and the extra
+        names being poorly normalized prior to PEP 685. If you want to perform
+        logic operations on extras, use :func:`is_extra_provided` instead.
+        """
+        raise NotImplementedError()
+
+    def is_extra_provided(self, extra: str) -> bool:
+        """Check whether an extra is provided by this distribution.
+
+        This is needed mostly for compatibility issues with pkg_resources not
+        following the extra normalization rules defined in PEP 685.
         """
         raise NotImplementedError()
 
@@ -537,10 +549,11 @@ def _iter_egg_info_extras(self) -> Iterable[str]:
         """Get extras from the egg-info directory."""
         known_extras = {""}
         for entry in self._iter_requires_txt_entries():
-            if entry.extra in known_extras:
+            extra = canonicalize_name(entry.extra)
+            if extra in known_extras:
                 continue
-            known_extras.add(entry.extra)
-            yield entry.extra
+            known_extras.add(extra)
+            yield extra
 
     def _iter_egg_info_dependencies(self) -> Iterable[str]:
         """Get distribution dependencies from the egg-info directory.
@@ -556,10 +569,11 @@ def _iter_egg_info_dependencies(self) -> Iterable[str]:
         all currently available PEP 517 backends, although not standardized.
         """
         for entry in self._iter_requires_txt_entries():
-            if entry.extra and entry.marker:
-                marker = f'({entry.marker}) and extra == "{safe_extra(entry.extra)}"'
-            elif entry.extra:
-                marker = f'extra == "{safe_extra(entry.extra)}"'
+            extra = canonicalize_name(entry.extra)
+            if extra and entry.marker:
+                marker = f'({entry.marker}) and extra == "{extra}"'
+            elif extra:
+                marker = f'extra == "{extra}"'
             elif entry.marker:
                 marker = entry.marker
             else:

src/pip/_internal/metadata/importlib/__init__.py

@@ -1,4 +1,6 @@
 from ._dists import Distribution
 from ._envs import Environment
 
-__all__ = ["Distribution", "Environment"]
+__all__ = ["NAME", "Distribution", "Environment"]
+
+NAME = "importlib"

src/pip/_internal/metadata/importlib/_dists.py

@@ -207,7 +207,13 @@ def _metadata_impl(self) -> email.message.Message:
         return cast(email.message.Message, self._dist.metadata)
 
     def iter_provided_extras(self) -> Iterable[str]:
-        return (extra for extra in self.metadata.get_all("Provides-Extra", []))
+        return self.metadata.get_all("Provides-Extra", [])
+
+    def is_extra_provided(self, extra: str) -> bool:
+        return any(
+            canonicalize_name(provided_extra) == canonicalize_name(extra)
+            for provided_extra in self.metadata.get_all("Provides-Extra", [])
+        )
 
     def iter_dependencies(self, extras: Collection[str] = ()) -> Iterable[Requirement]:
         contexts: Sequence[Dict[str, str]] = [{"extra": e} for e in extras]

src/pip/_internal/metadata/pkg_resources.py

@@ -24,8 +24,12 @@
     Wheel,
 )
 
+__all__ = ["NAME", "Distribution", "Environment"]
+
 logger = logging.getLogger(__name__)
 
+NAME = "pkg_resources"
+
 
 class EntryPoint(NamedTuple):
     name: str
@@ -212,12 +216,16 @@ def _metadata_impl(self) -> email.message.Message:
 
     def iter_dependencies(self, extras: Collection[str] = ()) -> Iterable[Requirement]:
         if extras:  # pkg_resources raises on invalid extras, so we sanitize.
-            extras = frozenset(extras).intersection(self._dist.extras)
+            extras = frozenset(pkg_resources.safe_extra(e) for e in extras)
+            extras = extras.intersection(self._dist.extras)
         return self._dist.requires(extras)
 
     def iter_provided_extras(self) -> Iterable[str]:
         return self._dist.extras
 
+    def is_extra_provided(self, extra: str) -> bool:
+        return pkg_resources.safe_extra(extra) in self._dist.extras
+
 
 class Environment(BaseEnvironment):
     def __init__(self, ws: pkg_resources.WorkingSet) -> None:

src/pip/_internal/req/req_install.py

@@ -272,7 +272,11 @@ def match_markers(self, extras_requested: Optional[Iterable[str]] = None) -> boo
             extras_requested = ("",)
         if self.markers is not None:
             return any(
-                self.markers.evaluate({"extra": safe_extra(extra)})
+                self.markers.evaluate({"extra": extra})
+                # TODO: Remove these two variants when packaging is upgraded to
+                # support the marker comparison logic specified in PEP 685.
+                or self.markers.evaluate({"extra": safe_extra(extra)})
+                or self.markers.evaluate({"extra": canonicalize_name(extra)})
                 for extra in extras_requested
             )
         else:

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

@@ -435,7 +435,8 @@ def __init__(
         # since PEP 685 has not been implemented for marker-matching, and using
         # the non-normalized extra for lookup ensures the user can select a
         # non-normalized extra in a package with its non-normalized form.
-        # TODO: Remove this when packaging is upgraded to support PEP 685.
+        # TODO: Remove this attribute when packaging is upgraded to support the
+        # marker comparison logic specified in PEP 685.
         self._unnormalized_extras = extras.difference(self.extras)
 
     def __str__(self) -> str:
@@ -490,18 +491,20 @@ def source_link(self) -> Optional[Link]:
     def _warn_invalid_extras(
         self,
         requested: FrozenSet[str],
-        provided: FrozenSet[str],
+        valid: FrozenSet[str],
     ) -> None:
         """Emit warnings for invalid extras being requested.
 
         This emits a warning for each requested extra that is not in the
         candidate's ``Provides-Extra`` list.
         """
-        invalid_extras_to_warn = requested.difference(
-            provided,
+        invalid_extras_to_warn = frozenset(
+            extra
+            for extra in requested
+            if extra not in valid
             # If an extra is requested in an unnormalized form, skip warning
             # about the normalized form being missing.
-            (canonicalize_name(e) for e in self._unnormalized_extras),
+            and extra in self.extras
         )
         if not invalid_extras_to_warn:
             return
@@ -521,9 +524,13 @@ def _calculate_valid_requested_extras(self) -> FrozenSet[str]:
         cause a warning to be logged here.
         """
         requested_extras = self.extras.union(self._unnormalized_extras)
-        provided_extras = frozenset(self.base.dist.iter_provided_extras())
-        self._warn_invalid_extras(requested_extras, provided_extras)
-        return requested_extras.intersection(provided_extras)
+        valid_extras = frozenset(
+            extra
+            for extra in requested_extras
+            if self.base.dist.is_extra_provided(extra)
+        )
+        self._warn_invalid_extras(requested_extras, valid_extras)
+        return valid_extras
 
     def iter_dependencies(self, with_requires: bool) -> Iterable[Optional[Requirement]]:
         factory = self.base._factory