From 0578b4ea06e6e44e9152d9b2f82f989348817221 Mon Sep 17 00:00:00 2001
From: Manuel Barkhau <mbarkhau@gmail.com>
Date: Thu, 27 Aug 2020 07:28:20 +0000
Subject: [PATCH] fix 1631 and add test

---
 CHANGES.md            |  2 ++
 src/black/__init__.py |  3 ++-
 tests/test_black.py   | 18 ++++++++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index 7352b857075..1c53604d4d5 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -7,6 +7,8 @@
 - `Black` now respects `--skip-string-normalization` when normalizing multiline
   docstring quotes (#1637)
 
+- fixed a crash when PWD=/ on POSIX (#1631)
+
 ### 20.8b1
 
 #### _Packaging_
diff --git a/src/black/__init__.py b/src/black/__init__.py
index 34d8145c0f7..048e771ce96 100644
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -5831,7 +5831,8 @@ def normalize_path_maybe_ignore(
     `report` is where "path ignored" output goes.
     """
     try:
-        normalized_path = path.resolve().relative_to(root).as_posix()
+        abspath = path if path.is_absolute() else Path.cwd() / path
+        normalized_path = abspath.resolve().relative_to(root).as_posix()
     except OSError as e:
         report.path_ignored(path, f"cannot be read because {e}")
         return None
diff --git a/tests/test_black.py b/tests/test_black.py
index 629afc5b0ad..bc80c8fca8b 100644
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -9,6 +9,7 @@
 from io import BytesIO, TextIOWrapper
 import os
 from pathlib import Path
+from platform import system
 import regex as re
 import sys
 from tempfile import TemporaryDirectory
@@ -1939,6 +1940,23 @@ def test_find_project_root(self) -> None:
             self.assertEqual(black.find_project_root((src_dir,)), src_dir.resolve())
             self.assertEqual(black.find_project_root((src_python,)), src_dir.resolve())
 
+    def test_bpo_33660_workaround(self) -> None:
+        if system() == "Windows":
+            return
+
+        # https://bugs.python.org/issue33660
+
+        old_cwd = Path.cwd()
+        try:
+            root = Path("/")
+            os.chdir(str(root))
+            path = Path("workspace") / "project"
+            report = black.Report(verbose=True)
+            normalized_path = black.normalize_path_maybe_ignore(path, root, report)
+            self.assertEqual(normalized_path, "workspace/project")
+        finally:
+            os.chdir(str(old_cwd))
+
 
 class BlackDTestCase(AioHTTPTestCase):
     async def get_application(self) -> web.Application: