Chose metadata generator in prepare_metadata

src/pip/_internal/operations/build/metadata.py

@@ -5,8 +5,6 @@
 import logging
 import os
 
-from pip._internal.operations.build.metadata_legacy import \
-    generate_metadata as _generate_metadata_legacy
 from pip._internal.utils.subprocess import runner_with_spinner_message
 from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
@@ -19,17 +17,10 @@
 
 def generate_metadata(install_req):
     # type: (InstallRequirement) -> str
-    """Generate metadata and return the metadata directory.
-    """
-    func = _generate_metadata
-    if not install_req.use_pep517:
-        func = _generate_metadata_legacy
-
-    return func(install_req)
-
+    """Generate metadata using mechanisms described in PEP 517.
 
-def _generate_metadata(install_req):
-    # type: (InstallRequirement) -> str
+    Returns the generated metadata directory.
+    """
     assert install_req.pep517_backend is not None
     build_env = install_req.build_env
     backend = install_req.pep517_backend

src/pip/_internal/operations/build/metadata_legacy.py

@@ -80,6 +80,10 @@ def depth_of_directory(dir_):
 
 def generate_metadata(install_req):
     # type: (InstallRequirement) -> str
+    """Generate metadata using setup.py-based defacto mechanisms.ArithmeticError
+
+    Returns the generated metadata directory.
+    """
     assert install_req.unpacked_source_directory
 
     req_details_str = install_req.name or "from {}".format(install_req.link)

src/pip/_internal/req/req_install.py

@@ -25,6 +25,8 @@
 from pip._internal.locations import distutils_scheme
 from pip._internal.models.link import Link
 from pip._internal.operations.build.metadata import generate_metadata
+from pip._internal.operations.build.metadata_legacy import \
+    generate_metadata as generate_metadata_legacy
 from pip._internal.pyproject import load_pyproject_toml, make_pyproject_path
 from pip._internal.req.req_uninstall import UninstallPathSet
 from pip._internal.utils.compat import native_str
@@ -615,8 +617,12 @@ def prepare_metadata(self):
         """
         assert self.source_dir
 
+        metadata_generator = generate_metadata
+        if not self.use_pep517:
+            metadata_generator = generate_metadata_legacy
+
         with indent_log():
-            self.metadata_directory = generate_metadata(self)
+            self.metadata_directory = metadata_generator(self)
 
         # Act on the newly generated metadata, based on the name and version.
         if not self.name: