Basic abstraction and one migration

src/pip/_internal/metadata/__init__.py

@@ -0,0 +1,16 @@
+from pip._internal.utils.compat import lru_cache
+from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+if MYPY_CHECK_RUNNING:
+    from typing import List, Optional
+
+    from .base import BaseEnvironment
+
+
+@lru_cache(maxsize=None)
+def get_environment(paths=None):
+    # type: (Optional[List[str]]) -> BaseEnvironment
+    from .pkg_resources import Environment
+    if paths is None:
+        return Environment.default()
+    return Environment.from_paths(paths)

src/pip/_internal/metadata/base.py

@@ -0,0 +1,35 @@
+import abc
+
+from pip._vendor.six import add_metaclass
+
+from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+if MYPY_CHECK_RUNNING:
+    from typing import List, Optional
+
+
+@add_metaclass(abc.ABCMeta)
+class BaseDistribution(object):
+    @property
+    def installer(self):
+        # type: () -> str
+        raise NotImplementedError()
+
+
+@add_metaclass(abc.ABCMeta)
+class BaseEnvironment(object):
+    """An environment containing distributions to introspect.
+    """
+    @classmethod
+    def default(cls):
+        # type: () -> BaseEnvironment
+        raise NotImplementedError()
+
+    @classmethod
+    def from_paths(cls, paths):
+        # type: (List[str]) -> BaseEnvironment
+        raise NotImplementedError()
+
+    def get_distribution(self, name):
+        # type: (str) -> Optional[BaseDistribution]
+        raise NotImplementedError()

src/pip/_internal/metadata/pkg_resources.py

@@ -0,0 +1,46 @@
+from pip._vendor import pkg_resources
+
+from pip._internal.utils.packaging import get_installer
+from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+from .base import BaseDistribution, BaseEnvironment
+
+if MYPY_CHECK_RUNNING:
+    from typing import List, Optional
+
+
+class Distribution(BaseDistribution):
+    def __init__(self, dist):
+        # type: (pkg_resources.Distribution) -> None
+        self._dist = dist
+
+    @property
+    def installer(self):
+        # type: () -> str
+        # TODO: Move get_installer() implementation here.
+        return get_installer(self._dist)
+
+
+class Environment(BaseEnvironment):
+    def __init__(self, ws):
+        # type: (pkg_resources.WorkingSet) -> None
+        self._ws = ws
+
+    @classmethod
+    def default(cls):
+        # type: () -> BaseEnvironment
+        return cls(pkg_resources.working_set)
+
+    @classmethod
+    def from_paths(cls, paths):
+        # type: (List[str]) -> BaseEnvironment
+        return cls(pkg_resources.WorkingSet(paths))
+
+    def get_distribution(self, name):
+        # type: (str) -> Optional[BaseDistribution]
+        req = pkg_resources.Requirement(name)
+        try:
+            dist = self._ws.find(req)
+        except pkg_resources.DistributionNotFound:
+            return None
+        return Distribution(dist)

src/pip/_internal/self_outdated_check.py

@@ -10,12 +10,12 @@
 import os.path
 import sys
 
-from pip._vendor import pkg_resources
 from pip._vendor.packaging import version as packaging_version
 from pip._vendor.six import ensure_binary
 
 from pip._internal.index.collector import LinkCollector
 from pip._internal.index.package_finder import PackageFinder
+from pip._internal.metadata import get_environment
 from pip._internal.models.search_scope import SearchScope
 from pip._internal.models.selection_prefs import SelectionPreferences
 from pip._internal.utils.filesystem import (
@@ -28,7 +28,6 @@
     get_installed_version,
     redact_auth_from_url,
 )
-from pip._internal.utils.packaging import get_installer
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
@@ -149,11 +148,8 @@ def was_installed_by_pip(pkg):
     This is used not to display the upgrade message when pip is in fact
     installed by system package manager, such as dnf on Fedora.
     """
-    try:
-        dist = pkg_resources.get_distribution(pkg)
-        return "pip" == get_installer(dist)
-    except pkg_resources.DistributionNotFound:
-        return False
+    dist = get_environment().get_distribution(pkg)
+    return dist is not None and "pip" == dist.installer
 
 
 def pip_self_version_check(session, options):