build_meta: Allow dist-info and egg-info to coexist

PEP 517 does not care if other directories/files are left behind in the
`metadata_directory`, as long as a `.dist_info` directory is produced at
the root. We can leave the `.egg-info` directory behind, so this way
we don't have to run it again when listing files from `build_py`.

3 files changed, 45 insertions, 45 deletions

diff --git a/setuptools/_path.py b/setuptools/_path.py
index ede9cb00..3767523b 100644
--- a/setuptools/_path.py
+++ b/setuptools/_path.py
@@ -1,7 +1,29 @@
 import os
+from typing import Union
+
+_Path = Union[str, os.PathLike]
 
 
 def ensure_directory(path):
     """Ensure that the parent directory of `path` exists"""
     dirname = os.path.dirname(path)
     os.makedirs(dirname, exist_ok=True)
+
+
+def same_path(p1: _Path, p2: _Path) -> bool:
+    """Differs from os.path.samefile because it does not require paths to exist.
+    Purely string based (no comparison between i-nodes).
+    >>> same_path("a/b", "./a/b")
+    True
+    >>> same_path("a/b", "a/./b")
+    True
+    >>> same_path("a/b", "././a/b")
+    True
+    >>> same_path("a/b", "./a/b/c/..")
+    True
+    >>> same_path("a/b", "../a/b/c")
+    False
+    >>> same_path("a", "a/b")
+    False
+    """
+    return os.path.normpath(p1) == os.path.normpath(p2)
diff --git a/setuptools/build_meta.py b/setuptools/build_meta.py
index f39a5a62..8e2af261 100644
--- a/setuptools/build_meta.py
+++ b/setuptools/build_meta.py
@@ -40,6 +40,7 @@ from typing import Dict, Iterator, List, Optional, Union
 
 import setuptools
 import distutils
+from ._path import same_path
 from ._reqs import parse_strings
 from ._deprecation_warning import SetuptoolsDeprecationWarning
 from distutils.util import strtobool
@@ -341,6 +342,23 @@ class _BuildMetaBackend(_ConfigSettingsTranslator):
     def get_requires_for_build_sdist(self, config_settings=None):
         return self._get_build_requires(config_settings, requirements=[])
 
+    def _bubble_up_info_directory(self, metadata_directory: str, suffix: str) -> str:
+        """
+        PEP 517 requires that the .dist-info directory be placed in the
+        metadata_directory. To comply, we MUST copy the directory to the root.
+
+        Returns the basename of the info directory, e.g. `proj-0.0.0.dist-info`.
+        """
+        candidates = list(Path(metadata_directory).glob(f"**/*{suffix}/"))
+        assert len(candidates) == 1, f"Exactly one {suffix} should have been produced"
+        info_dir = candidates[0]
+
+        if not same_path(info_dir.parent, metadata_directory):
+            shutil.move(str(info_dir), metadata_directory)
+            # PEP 517 allow other files and dirs to exist in metadata_directory
+
+        return info_dir.name
+
     def prepare_metadata_for_build_wheel(self, metadata_directory,
                                          config_settings=None):
         sys.argv = [
@@ -348,36 +366,13 @@ class _BuildMetaBackend(_ConfigSettingsTranslator):
             *self._global_args(config_settings),
             "dist_info",
             "--output-dir", metadata_directory,
+            "--keep-egg-info",
         ]
         with no_install_setup_requires():
             self.run_setup()
 
-        dist_info_directory = metadata_directory
-        while True:
-            dist_infos = [f for f in os.listdir(dist_info_directory)
-                          if f.endswith('.dist-info')]
-
-            if (
-                len(dist_infos) == 0 and
-                len(_get_immediate_subdirectories(dist_info_directory)) == 1
-            ):
-
-                dist_info_directory = os.path.join(
-                    dist_info_directory, os.listdir(dist_info_directory)[0])
-                continue
-
-            assert len(dist_infos) == 1
-            break
-
-        # PEP 517 requires that the .dist-info directory be placed in the
-        # metadata_directory. To comply, we MUST copy the directory to the root
-        if dist_info_directory != metadata_directory:
-            shutil.move(
-                os.path.join(dist_info_directory, dist_infos[0]),
-                metadata_directory)
-            shutil.rmtree(dist_info_directory, ignore_errors=True)
-
-        return dist_infos[0]
+        self._bubble_up_info_directory(metadata_directory, ".egg-info")
+        return self._bubble_up_info_directory(metadata_directory, ".dist-info")
 
     def _build_with_temp_dir(self, setup_command, result_extension,
                              result_directory, config_settings):
diff --git a/setuptools/config/expand.py b/setuptools/config/expand.py
index da55d4ee..6ea54969 100644
--- a/setuptools/config/expand.py
+++ b/setuptools/config/expand.py
@@ -43,6 +43,8 @@ from types import ModuleType
 
 from distutils.errors import DistutilsOptionError
 
+from .._path import same_path as _same_path
+
 if TYPE_CHECKING:
     from setuptools.dist import Distribution  # noqa
     from setuptools.discovery import ConfigDiscovery  # noqa
@@ -330,25 +332,6 @@ def find_packages(
     return packages
 
 
-def _same_path(p1: _Path, p2: _Path) -> bool:
-    """Differs from os.path.samefile because it does not require paths to exist.
-    Purely string based (no comparison between i-nodes).
-    >>> _same_path("a/b", "./a/b")
-    True
-    >>> _same_path("a/b", "a/./b")
-    True
-    >>> _same_path("a/b", "././a/b")
-    True
-    >>> _same_path("a/b", "./a/b/c/..")
-    True
-    >>> _same_path("a/b", "../a/b/c")
-    False
-    >>> _same_path("a", "a/b")
-    False
-    """
-    return os.path.normpath(p1) == os.path.normpath(p2)
-
-
 def _nest_path(parent: _Path, path: _Path) -> str:
     path = parent if path in {".", ""} else os.path.join(parent, path)
     return os.path.normpath(path)