Bazaar: Export directly from the remote branch.

This significantly improves performance, since it allows the remote
server to directly stream a tarball that just contains the requested
revision rather than the full repository contents.

.travis.yml

@@ -2,6 +2,10 @@ language: python
 cache: pip
 dist: xenial
 python: 3.6
+addons:
+  apt:
+    packages:
+    - bzr
 
 stages:
 - primary

news/5443.feature

@@ -0,0 +1 @@
+Avoid creating an unnecessary local clone of a Bazaar branch when exporting.

src/pip/_internal/vcs/bazaar.py

@@ -9,7 +9,6 @@
 from pip._internal.utils.misc import (
     display_path, make_vcs_requirement_url, rmtree,
 )
-from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.vcs import VersionControl, vcs
 
 logger = logging.getLogger(__name__)
@@ -42,13 +41,11 @@ def export(self, location):
         if os.path.exists(location):
             rmtree(location)
 
-        with TempDirectory(kind="export") as temp_dir:
-            self.unpack(temp_dir.path)
-
-            self.run_command(
-                ['export', location],
-                cwd=temp_dir.path, show_stdout=False,
-            )
+        url, rev_options = self.get_url_rev_options(self.url)
+        self.run_command(
+            ['export', location, url] + rev_options.to_args(),
+            show_stdout=False,
+        )
 
     def fetch_new(self, dest, url, rev_options):
         rev_display = rev_options.to_display()

tests/functional/test_vcs_bazaar.py

@@ -0,0 +1,25 @@
+"""
+Contains functional tests of the Bazaar class.
+"""
+
+import os
+
+from pip._internal.vcs.bazaar import Bazaar
+from tests.lib import _test_path_to_file_url, _vcs_add, create_file, need_bzr
+
+
+@need_bzr
+def test_export(script, tmpdir):
+    """Test that a Bazaar branch can be exported."""
+    branch_path = tmpdir / 'test-branch'
+    branch_path.mkdir()
+
+    create_file(branch_path / 'test_file', 'something')
+
+    _vcs_add(script, str(branch_path), vcs='bazaar')
+
+    bzr = Bazaar('bzr+' + _test_path_to_file_url(branch_path))
+    export_dir = str(tmpdir / 'export')
+    bzr.export(export_dir)
+
+    assert os.listdir(export_dir) == ['test_file']