[commands/cache] make pip cache purge remove everything from http +…

… wheels caches; make `pip cache remove` prune empty directories.

src/pip/_internal/commands/cache.py

@@ -180,7 +180,21 @@ def remove_cache_items(self, options: Values, args: List[Any]) -> None:
         for filename in files:
             os.unlink(filename)
             logger.verbose("Removed %s", filename)
+
+        dirs = filesystem.list_empty_subdirs(
+            self._cache_dir(options, "http")
+        ) + filesystem.list_empty_subdirs(self._cache_dir(options, "wheels"))
+        for dirname in dirs:
+            os.rmdir(dirname)
+
+        # selfcheck.json is no longer used by pip.
+        selfcheck_json = self._cache_dir(options, "selfcheck.json")
+        if os.path.isfile(selfcheck_json):
+            os.remove(selfcheck_json)
+            logger.verbose("Removed legacy selfcheck.json file")
+
         logger.info("Files removed: %s", len(files))
+        logger.info("Empty directories removed: %s", len(dirs))
 
     def purge_cache(self, options: Values, args: List[Any]) -> None:
         if args:

src/pip/_internal/utils/filesystem.py

@@ -180,3 +180,12 @@ def directory_size(path: str) -> Union[int, float]:
 
 def format_directory_size(path: str) -> str:
     return format_size(directory_size(path))
+
+
+def list_empty_subdirs(path):
+    # type: (str) -> List[str]
+    """Returns a list of absolute paths of empty directories beneath path."""
+    result = []  # type: List[str]
+    for root, dirs, _files in os.walk(path, topdown=False):
+        result.extend(os.path.join(root, d) for d in dirs)
+    return result