Fix upgrade of VCS requirement with otherwise nonexistent egg. Fixes #486.

docs/news.txt

@@ -13,6 +13,9 @@ Beta and final releases planned for the second half of 2012.
 master (unreleased)
 -------------------
 
+* Fixed issue #486 - fix upgrade from VCS url of otherwise nonexistent egg.
+  Thanks aknapp for the report.
+
 * Fixed issue #427 - clearer error message on a malformed VCS url. Thanks
   Thomas Fenzl.
 

pip/req.py

@@ -7,7 +7,8 @@ import pkg_resources
 import tempfile
 from pip.locations import bin_py, running_under_virtualenv
 from pip.exceptions import (InstallationError, UninstallationError,
-                            BestVersionAlreadyInstalled)
+                            BestVersionAlreadyInstalled,
+                            DistributionNotFound)
 from pip.vcs import vcs
 from pip.log import logger
 from pip.util import display_path, rmtree
@@ -910,6 +911,7 @@ class RequirementSet(object):
                 req_to_install = reqs.pop(0)
             install = True
             best_installed = False
+            not_found = None
             if not self.ignore_installed and not req_to_install.editable:
                 req_to_install.check_if_exists()
                 if req_to_install.satisfied_by:
@@ -921,6 +923,8 @@ class RequirementSet(object):
                             except BestVersionAlreadyInstalled:
                                 best_installed = True
                                 install = False
+                            except DistributionNotFound:
+                                not_found = sys.exc_info()[1]
                             else:
                                 # Avoid the need to call find_requirement again
                                 req_to_install.url = url.url
@@ -975,6 +979,8 @@ class RequirementSet(object):
                     if not os.path.exists(os.path.join(location, 'setup.py')):
                         ## FIXME: this won't upgrade when there's an existing package unpacked in `location`
                         if req_to_install.url is None:
+                            if not_found:
+                                raise not_found
                             url = finder.find_requirement(req_to_install, upgrade=self.upgrade)
                         else:
                             ## FIXME: should req_to_install.url already be a link?

tests/test_upgrade.py

@@ -3,6 +3,7 @@ from os.path import join
 from tests.test_pip import (here, reset_env, run_pip, assert_all_changes,
                             write_file, pyversion, _create_test_package,
                             _change_test_package_version)
+from tests.local_repos import local_checkout
 
 
 def test_no_upgrade_unless_requested():
@@ -190,3 +191,12 @@ def test_install_with_ignoreinstalled_requested():
     assert result.files_created, 'pip install -I did not install'
     assert env.site_packages/'INITools-0.1-py%s.egg-info' % pyversion not in result.files_created
 
+
+def test_upgrade_vcs_req_with_no_dists_found():
+    """It can upgrade a VCS requirement that has no distributions otherwise."""
+    reset_env()
+    req = "%s#egg=pip-test-package" % local_checkout(
+        "git+http://github.com/pypa/pip-test-package.git")
+    run_pip("install", req)
+    result = run_pip("install", "-U", req)
+    assert not result.returncode