From 8d963638825aceeaa06bf350685e4ac1d4cccd12 Mon Sep 17 00:00:00 2001
From: Dustin Ingram <di@users.noreply.github.com>
Date: Fri, 29 Sep 2017 17:30:30 -0500
Subject: [PATCH] Don't assume master branch exists when reinstalling editable
 package from Git (#4450)

* Add failing test

* Don't assume master branch is default

* Don't expect output to stderr

* Use the 'short ref' instead of the 'full ref'
---
 news/4448.bugfix                     |  2 ++
 src/pip/_internal/vcs/git.py         |  2 +-
 tests/functional/test_install_vcs.py | 29 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 news/4448.bugfix

diff --git a/news/4448.bugfix b/news/4448.bugfix
new file mode 100644
index 00000000000..28088dd6301
--- /dev/null
+++ b/news/4448.bugfix
@@ -0,0 +1,2 @@
+Reinstalling an editable package from Git no longer assumes that the ``master``
+branch exists.
diff --git a/src/pip/_internal/vcs/git.py b/src/pip/_internal/vcs/git.py
index 6262f2729de..b7b12817772 100644
--- a/src/pip/_internal/vcs/git.py
+++ b/src/pip/_internal/vcs/git.py
@@ -132,7 +132,7 @@ def obtain(self, dest):
             rev_options = [rev]
             rev_display = ' (to %s)' % rev
         else:
-            rev_options = ['origin/master']
+            rev_options = ['origin/HEAD']
             rev_display = ''
         if self.check_destination(dest, url, rev_options, rev_display):
             logger.info(
diff --git a/tests/functional/test_install_vcs.py b/tests/functional/test_install_vcs.py
index d8175331e7d..4845f91ad1f 100644
--- a/tests/functional/test_install_vcs.py
+++ b/tests/functional/test_install_vcs.py
@@ -253,3 +253,32 @@ def test_git_works_with_editable_non_origin_repo(script):
     assert "Error when trying to get requirement" in result.stderr
     assert "Could not determine repository location" in result.stdout
     assert "version-pkg==0.1" in result.stdout
+
+
+@pytest.mark.network
+def test_reinstalling_works_with_editible_non_master_branch(script):
+    """
+    Reinstalling an editable installation should not assume that the "master"
+    branch exists. See https://github.com/pypa/pip/issues/4448.
+    """
+    version_pkg_path = _create_test_package(script)
+
+    # Switch the default branch to something other than 'master'
+    script.run('git', 'branch', '-m', 'foobar', cwd=version_pkg_path)
+
+    script.pip(
+        'install', '-e',
+        '%s#egg=version_pkg' %
+        ('git+file://' + version_pkg_path.abspath.replace('\\', '/')),
+    )
+    version = script.run('version_pkg')
+    assert '0.1' in version.stdout
+
+    _change_test_package_version(script, version_pkg_path)
+    script.pip(
+        'install', '-e',
+        '%s#egg=version_pkg' %
+        ('git+file://' + version_pkg_path.abspath.replace('\\', '/')),
+    )
+    version = script.run('version_pkg')
+    assert 'some different version' in version.stdout