Address issue #1130: make pip ignore GIT_DIR and GIT_WORK_TREE.

news/1130.bugfix

@@ -0,0 +1,2 @@
+Allow pip to work if the ``GIT_DIR`` and ``GIT_WORK_TREE`` environment
+variables are set.

src/pip/_internal/utils/misc.py

@@ -627,7 +627,14 @@ def unpack_file(filename, location, content_type, link):
 def call_subprocess(cmd, show_stdout=True, cwd=None,
                     on_returncode='raise',
                     command_desc=None,
-                    extra_environ=None, spinner=None):
+                    extra_environ=None, unset_environ=None, spinner=None):
+    """
+    Args:
+      unset_environ: an iterable of environment variable names to unset
+        prior to calling subprocess.Popen().
+    """
+    if unset_environ is None:
+        unset_environ = []
     # This function's handling of subprocess output is confusing and I
     # previously broke it terribly, so as penance I will write a long comment
     # explaining things.
@@ -664,6 +671,8 @@ def call_subprocess(cmd, show_stdout=True, cwd=None,
     env = os.environ.copy()
     if extra_environ:
         env.update(extra_environ)
+    for name in unset_environ:
+        env.pop(name, None)
     try:
         proc = subprocess.Popen(
             cmd, stderr=subprocess.STDOUT, stdin=None, stdout=stdout,

src/pip/_internal/vcs/__init__.py

@@ -166,6 +166,8 @@ class VersionControl(object):
     dirname = ''
     # List of supported schemes for this Version Control
     schemes = ()  # type: Tuple[str, ...]
+    # Iterable of environment variable names to pass to call_subprocess().
+    unset_environ = ()
     default_arg_rev = None  # type: Optional[str]
 
     def __init__(self, url=None, *args, **kwargs):
@@ -422,7 +424,8 @@ class VersionControl(object):
             return call_subprocess(cmd, show_stdout, cwd,
                                    on_returncode,
                                    command_desc, extra_environ,
-                                   spinner)
+                                   unset_environ=self.unset_environ,
+                                   spinner=spinner)
         except OSError as e:
             # errno.ENOENT = no such file or directory
             # In other words, the VCS executable isn't available

src/pip/_internal/vcs/git.py

@@ -27,6 +27,9 @@ class Git(VersionControl):
     schemes = (
         'git', 'git+http', 'git+https', 'git+ssh', 'git+git', 'git+file',
     )
+    # Prevent the user's environment variables from interfering with pip:
+    # https://github.com/pypa/pip/issues/1130
+    unset_environ = ('GIT_DIR', 'GIT_WORK_TREE')
     default_arg_rev = 'origin/HEAD'
 
     def __init__(self, url=None, *args, **kwargs):