BUG: look for dist-infos in subdirectories

This code is a bit ugly, but it's also been tested with the pip test suite
It's not the best solution long term (the best solution is to get the egg_info
directory directly from egg_info), but it works for now and avoids
technical risk.

setuptools/build_meta.py

@@ -93,6 +93,11 @@ def _get_build_requires(config_settings):
     return requirements
 
 
+def _get_immediate_subdirectories(a_dir):
+    return [name for name in os.listdir(a_dir)
+            if os.path.isdir(os.path.join(a_dir, name))]
+
+
 def get_requires_for_build_wheel(config_settings=None):
     config_settings = _fix_config(config_settings)
     return _get_build_requires(config_settings)
@@ -106,11 +111,29 @@ def get_requires_for_build_sdist(config_settings=None):
 def prepare_metadata_for_build_wheel(metadata_directory, config_settings=None):
     sys.argv = sys.argv[:1] + ['dist_info', '--egg-base', metadata_directory]
     _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)
 
-    dist_infos = [f for f in os.listdir(metadata_directory)
-                  if f.endswith('.dist-info')]
-
-    assert len(dist_infos) == 1
     return dist_infos[0]