Fix pre-commit install on subst drives

pre_commit/git.py

@@ -52,10 +52,10 @@ def get_root() -> str:
     # "rev-parse --show-cdup" to get the appropriate path, but must perform
     # an extra check to see if we are in the .git directory.
     try:
-        root = os.path.realpath(
+        root = os.path.abspath(
             cmd_output('git', 'rev-parse', '--show-cdup')[1].strip(),
         )
-        git_dir = os.path.realpath(get_git_dir())
+        git_dir = os.path.abspath(get_git_dir())
     except CalledProcessError:
         raise FatalError(
             'git failed. Is it installed, and are you in a Git repository '

tests/main_test.py

@@ -7,7 +7,9 @@ import pytest
 import pre_commit.constants as C
 from pre_commit import main
 from pre_commit.errors import FatalError
+from pre_commit.util import cmd_output
 from testing.auto_namedtuple import auto_namedtuple
+from testing.util import cwd
 
 
 @pytest.mark.parametrize(
@@ -54,6 +56,17 @@ def test_adjust_args_and_chdir_relative_things(in_git_dir):
     assert args.files == [os.path.join('foo', 'f1'), os.path.join('foo', 'f2')]
 
 
+@pytest.mark.skipif(os.name != 'nt', reason='windows feature')
+def test_install_on_subst(in_git_dir, store):  # pragma: posix no cover
+    assert not os.path.exists('Z:')
+    cmd_output('subst', 'Z:', str(in_git_dir))
+    try:
+        with cwd('Z:'):
+            test_adjust_args_and_chdir_noop('Z:\\')
+    finally:
+        cmd_output('subst', '/d', 'Z:')
+
+
 def test_adjust_args_and_chdir_non_relative_config(in_git_dir):
     in_git_dir.join('foo').ensure_dir().chdir()