Guard PackageFinder imports under TYPE_CHECKING in distributions

So freeze doesn't need to import the index/network modules.

Author: ichard26

src/pip/_internal/distributions/base.py

@@ -1,10 +1,12 @@
 import abc
-from typing import Optional
+from typing import TYPE_CHECKING, Optional
 
-from pip._internal.index.package_finder import PackageFinder
 from pip._internal.metadata.base import BaseDistribution
 from pip._internal.req import InstallRequirement
 
+if TYPE_CHECKING:
+    from pip._internal.index.package_finder import PackageFinder
+
 
 class AbstractDistribution(metaclass=abc.ABCMeta):
     """A base class for handling installable artifacts.
@@ -44,7 +46,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
     @abc.abstractmethod
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        finder: "PackageFinder",
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None:

src/pip/_internal/distributions/sdist.py

@@ -1,13 +1,15 @@
 import logging
-from typing import Iterable, Optional, Set, Tuple
+from typing import TYPE_CHECKING, Iterable, Optional, Set, Tuple
 
 from pip._internal.build_env import BuildEnvironment
 from pip._internal.distributions.base import AbstractDistribution
 from pip._internal.exceptions import InstallationError
-from pip._internal.index.package_finder import PackageFinder
 from pip._internal.metadata import BaseDistribution
 from pip._internal.utils.subprocess import runner_with_spinner_message
 
+if TYPE_CHECKING:
+    from pip._internal.index.package_finder import PackageFinder
+
 logger = logging.getLogger(__name__)
 
 
@@ -29,7 +31,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
 
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        finder: "PackageFinder",
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None:
@@ -66,7 +68,7 @@ def prepare_distribution_metadata(
                 self._raise_missing_reqs(missing)
         self.req.prepare_metadata()
 
-    def _prepare_build_backend(self, finder: PackageFinder) -> None:
+    def _prepare_build_backend(self, finder: "PackageFinder") -> None:
         # Isolate in a BuildEnvironment and install the build-time
         # requirements.
         pyproject_requires = self.req.pyproject_requires
@@ -110,7 +112,7 @@ def _get_build_requires_editable(self) -> Iterable[str]:
             with backend.subprocess_runner(runner):
                 return backend.get_requires_for_build_editable()
 
-    def _install_build_reqs(self, finder: PackageFinder) -> None:
+    def _install_build_reqs(self, finder: "PackageFinder") -> None:
         # Install any extra build dependencies that the backend requests.
         # This must be done in a second pass, as the pyproject.toml
         # dependencies must be installed before we can call the backend.

src/pip/_internal/distributions/wheel.py

@@ -1,15 +1,17 @@
-from typing import Optional
+from typing import TYPE_CHECKING, Optional
 
 from pip._vendor.packaging.utils import canonicalize_name
 
 from pip._internal.distributions.base import AbstractDistribution
-from pip._internal.index.package_finder import PackageFinder
 from pip._internal.metadata import (
     BaseDistribution,
     FilesystemWheel,
     get_wheel_distribution,
 )
 
+if TYPE_CHECKING:
+    from pip._internal.index.package_finder import PackageFinder
+
 
 class WheelDistribution(AbstractDistribution):
     """Represents a wheel distribution.
@@ -33,7 +35,7 @@ def get_metadata_distribution(self) -> BaseDistribution:
 
     def prepare_distribution_metadata(
         self,
-        finder: PackageFinder,
+        finder: "PackageFinder",
         build_isolation: bool,
         check_build_deps: bool,
     ) -> None: