Speed up unpack_file_url

E.g.: `pip install /path/to/dir`

by building an sdist and then unpacking it instead of doing
`shutil.copytree`. `shutil.copytree` may copy files that aren't included
in the sdist, which means that:

1. If those files are large, a `pip install` could take much longer than
it should.

2. Folks that are using `python setup.py install` to test their package
are not fully testing it, because it may copy over files that wouldn't
be there if they built and sdist and installed that.

So this method building an sdist is both more accurate and faster.

Fixes pypa#2195

pip/download.py

@@ -22,8 +22,10 @@
 from pip.exceptions import InstallationError, HashMismatch
 from pip.models import PyPI
 from pip.utils import (splitext, rmtree, format_size, display_path,
-                       backup_dir, ask_path_exists, unpack_file)
+                       backup_dir, ask_path_exists, unpack_file,
+                       call_subprocess)
 from pip.utils.filesystem import check_path_owner
+from pip.utils.logging import indent_log
 from pip.utils.ui import DownloadProgressBar, DownloadProgressSpinner
 from pip.locations import write_delete_marker_file
 from pip.vcs import vcs
@@ -725,6 +727,45 @@ def unpack_file_url(link, location, download_dir=None):
         _copy_file(from_path, download_dir, content_type, link)
 
 
+def _copy_dist_from_dir(link_path, location):
+    """Copy distribution files in `link_path` to `location`.
+
+    Invoked when user requests to install a local directory. E.g.:
+
+        pip install .
+        pip install ~/dev/git-repos/python-prompt-toolkit
+
+    """
+
+    # Note: This is currently VERY SLOW if you have a lot of data in the
+    # directory, because it copies everything with `shutil.copytree`.
+    # What it should really do is build an sdist and install that.
+    # See https://github.com/pypa/pip/issues/2195
+
+    if os.path.isdir(location):
+        rmtree(location)
+
+    # build an sdist
+    setup_py = 'setup.py'
+    sdist_args = [sys.executable]
+    sdist_args.append('-c')
+    sdist_args.append(
+        "import setuptools, tokenize;__file__=%r;"
+        "exec(compile(getattr(tokenize, 'open', open)(__file__).read()"
+        ".replace('\\r\\n', '\\n'), __file__, 'exec'))" % setup_py)
+    sdist_args.append('sdist')
+    sdist_args += ['--dist-dir', location]
+    logger.info('Running setup.py sdist for %s', link_path)
+
+    with indent_log():
+        call_subprocess(sdist_args, cwd=link_path, show_stdout=False)
+
+    # unpack sdist into `location`
+    sdist = os.path.join(location, os.listdir(location)[0])
+    logger.info('Unpacking sdist %s into %s', sdist, location)
+    unpack_file(sdist, location, content_type=None, link=None)
+
+
 class PipXmlrpcTransport(xmlrpc_client.Transport):
     """Provide a `xmlrpclib.Transport` implementation via a `PipSession`
     object.