fbcode_builder: getdeps: add copytree helper

Summary:
this module adds some functions that help with copying
directory trees.  The copytree function is aware of eden and will
issue a prefetch prior to walking the directory.

Reviewed By: simpkins

Differential Revision: D14691006

fbshipit-source-id: 079bf850756f61aca17978453d07bc73b2f91788

build/fbcode_builder/getdeps/copytree.py

@@ -0,0 +1,54 @@
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+import shutil
+import subprocess
+
+
+def is_eden(dirpath):
+    """Returns True if the specified directory is the root directory of,
+    or is a sub-directory of an Eden mount."""
+    return os.path.islink(os.path.join(dirpath, ".eden", "root"))
+
+
+def find_eden_root(dirpath):
+    """If the specified directory is the root directory of, or is a
+    sub-directory of an Eden mount, returns the canonical absolute path
+    to the root of that Eden mount."""
+    return os.readlink(os.path.join(dirpath, ".eden", "root"))
+
+
+def prefetch_dir_if_eden(dirpath):
+    """ After an amend/rebase, Eden may need to fetch a large number
+    of trees from the servers.  The simplistic single threaded walk
+    performed by copytree makes this more expensive than is desirable
+    so we help accelerate things by performing a prefetch on the
+    source directory """
+    if not is_eden(dirpath):
+        return
+    root = find_eden_root(dirpath)
+    rel = os.path.relpath(dirpath, root)
+    print("Prefetching %s..." % rel)
+    # TODO: this should be edenfsctl but until I swing through a new
+    # package deploy, I only have `eden` on my mac to test this
+    subprocess.call(["eden", "prefetch", "--repo", root, "--silent", "%s/**" % rel])
+
+
+def copytree(src_dir, dest_dir, ignore=None):
+    """ Recursively copy the src_dir to the dest_dir, filtering
+    out entries using the ignore lambda.  The behavior of the
+    ignore lambda must match that described by `shutil.copytree`.
+    This `copytree` function knows how to prefetch data when
+    running in an eden repo.
+    TODO: I'd like to either extend this or add a variant that
+    uses watchman to mirror src_dir into dest_dir.
+    """
+    prefetch_dir_if_eden(src_dir)
+    return shutil.copytree(src_dir, dest_dir, ignore=ignore)