Use email.message to parse metadata

src/pip/_internal/metadata/base.py

@@ -1,3 +1,4 @@
+import email.message
 import logging
 import re
 from typing import (
@@ -52,11 +53,6 @@ class BaseDistribution(Protocol):
         """
         raise NotImplementedError()
 
-    @property
-    def metadata_version(self) -> Optional[str]:
-        """Value of "Metadata-Version:" in the distribution, if available."""
-        raise NotImplementedError()
-
     @property
     def canonical_name(self) -> str:
         raise NotImplementedError()
@@ -89,12 +85,27 @@ class BaseDistribution(Protocol):
         """Read a file in the .dist-info (or .egg-info) directory."""
         raise NotImplementedError()
 
-    def iter_dependencies(self, extras: Collection[str]) -> Iterable[Requirement]:
-        raise NotImplementedError()
-
     def iter_entry_points(self) -> Iterable[BaseEntryPoint]:
         raise NotImplementedError()
 
+    @property
+    def metadata(self) -> email.message.Message:
+        """Metadata of distribution parsed from e.g. METADATA or PKG-INFO."""
+        raise NotImplementedError()
+
+    @property
+    def metadata_version(self) -> Optional[str]:
+        """Value of "Metadata-Version:" in the distribution, if available."""
+        return self.metadata.get("Metadata-Version")
+
+    def iter_dependencies(self, extras: Collection[str]) -> Iterable[Requirement]:
+        for value in self.metadata.get_all("Requires-Dist"):
+            requirement = Requirement(value)
+            marker = requirement.marker
+            if marker and any(marker.evaluate({"extra": extra}) for extra in extras):
+                continue
+            yield requirement
+
 
 class BaseEnvironment:
     """An environment containing distributions to introspect."""

src/pip/_internal/metadata/pkg_resources.py

@@ -1,4 +1,5 @@
 import logging
+import email.message
 import zipfile
 from typing import Collection, Iterable, Iterator, List, NamedTuple, Optional
 
@@ -10,7 +11,7 @@ from pip._vendor.packaging.version import parse as parse_version
 from pip._internal.models.direct_url import DirectUrl
 from pip._internal.utils import misc  # TODO: Move definition here.
 from pip._internal.utils.direct_url_helpers import dist_get_direct_url
-from pip._internal.utils.packaging import get_installer
+from pip._internal.utils.packaging import get_installer, get_metadata
 from pip._internal.utils.wheel import pkg_resources_distribution_for_wheel
 
 from .base import BaseDistribution, BaseEntryPoint, BaseEnvironment, DistributionVersion
@@ -38,13 +39,6 @@ class Distribution(BaseDistribution):
     def location(self) -> Optional[str]:
         return self._dist.location
 
-    @property
-    def metadata_version(self) -> Optional[str]:
-        for line in self._dist.get_metadata_lines(self._dist.PKG_INFO):
-            if line.lower().startswith("metadata-version:"):
-                return line.split(":", 1)[-1].strip()
-        return None
-
     @property
     def canonical_name(self) -> str:
         return canonicalize_name(self._dist.project_name)
@@ -73,18 +67,6 @@ class Distribution(BaseDistribution):
     def in_usersite(self) -> bool:
         return misc.dist_in_usersite(self._dist)
 
-    def iter_dependencies(self, extras: Collection[str]) -> Iterable[Requirement]:
-        # pkg_resources raises on invalid extras, so we sanitize.
-        requested_extras = set(extras)
-        valid_extras = requested_extras & set(self._dist.extras)
-        for invalid_extra in requested_extras ^ valid_extras:
-            logger.warning(
-                "Invalid extra %r for package %r discarded",
-                invalid_extra,
-                self.canonical_name,
-            )
-        return self._dist.requires(extras)
-
     def read_text(self, name: str) -> str:
         return self._dist.get_metadata(name)
 
@@ -94,6 +76,16 @@ class Distribution(BaseDistribution):
                 name, _, value = str(entry_point).partition("=")
                 yield EntryPoint(name=name.strip(), value=value.strip(), group=group)
 
+    @property
+    def metadata(self) -> email.message.Message:
+        return get_metadata(self._dist)
+
+    def iter_dependencies(self, extras: Collection[str]) -> Iterable[Requirement]:
+        """pkg_resources caches this for performance so we take advantage of it."""
+        if extras:  # pkg_resources raises on invalid extras, so we sanitize.
+            extras = set(extras).intersection(self._dist.extras)
+        return self._dist.requires(extras)
+
 
 class Environment(BaseEnvironment):
     def __init__(self, ws: pkg_resources.WorkingSet) -> None: