Add a spinner when preparing setup.py metadata

For symmetry with pyproject.toml metadata preparation.

Author: sbidoul

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

@@ -5,6 +5,7 @@
 import os
 
 from pip._internal.build_env import BuildEnvironment
+from pip._internal.cli.spinners import open_spinner
 from pip._internal.exceptions import InstallationError
 from pip._internal.utils.setuptools_build import make_setuptools_egg_info_args
 from pip._internal.utils.subprocess import call_subprocess
@@ -54,11 +55,13 @@ def generate_metadata(
     )
 
     with build_env:
-        call_subprocess(
-            args,
-            cwd=source_dir,
-            command_desc="python setup.py egg_info",
-        )
+        with open_spinner("Preparing metadata (setup.py)") as spinner:
+            call_subprocess(
+                args,
+                cwd=source_dir,
+                command_desc="python setup.py egg_info",
+                spinner=spinner,
+            )
 
     # Return the .egg-info directory.
     return _find_egg_info(egg_info_dir)

src/pip/_internal/req/req_install.py

@@ -528,6 +528,10 @@ def _generate_editable_metadata(self) -> str:
                 # At this point we have determined that the build_editable hook
                 # is missing, and there is a setup.py or setup.cfg
                 # so we fallback to the legacy metadata generation
+                logger.info(
+                    "Build backend does not support editables, "
+                    "falling back to setup.py egg_info."
+                )
             else:
                 self.supports_pyproject_editable = True
                 return metadata_directory