Fix on windows, maybe?

Author: plietar

src/outpack/util.py

@@ -84,9 +84,21 @@ def assert_file_exists(path, *, workdir=None, name="File"):
 
 def assert_relative_path(path: str, name: str):
     path = Path(path)
-    if path.is_absolute():
+
+    # On Windows, this is not equivalent to path.is_absolute().
+    # There are paths which are neither absolute nor relative, but somewhere
+    # between the two. These are paths such as `C:foo` or `\foo`. The former has
+    # a drive but no root, and the latter has a root but no drive. We want to
+    # exclude both scenarios. On POSIX, drive will always be empty and this is
+    # equivalent to calling `is_absolute()`.
+    #
+    # See https://github.com/python/cpython/issues/44626 for some discussion.
+    # Unfortunately, while the issue was closed, the `is_relative` function
+    # mentioned was never added.
+    if path.drive or path.root:
         msg = f"Expected {name} path '{path}' to be a relative path"
         raise Exception(msg)
+
     if ".." in path.parts:
         msg = f"Path '{path}' must not contain '..' component"
         raise Exception(msg)

tests/test_util.py

@@ -1,5 +1,6 @@
 import datetime
 import os
+import re
 
 import pytest
 
@@ -69,22 +70,34 @@ def test_can_test_for_relative_path():
     assert_relative_path("foo.txt", "file")
     assert_relative_path("dir/foo.txt", "file")
 
-    with pytest.raises(
-        Exception, match="Expected file path '/foo.txt' to be a relative path"
-    ):
+    msg = "Expected file path '/foo.txt' to be a relative path"
+    with pytest.raises(Exception, match=re.escape(msg)):
         assert_relative_path("/foo.txt", "file")
 
-    with pytest.raises(
-        Exception, match="Path '../foo.txt' must not contain '..' component"
-    ):
+    msg = "Path '../foo.txt' must not contain '..' component"
+    with pytest.raises(Exception, match=re.escape(msg)):
         assert_relative_path("../foo.txt", "file")
 
-    with pytest.raises(
-        Exception, match="Path 'aa/../foo.txt' must not contain '..' component"
-    ):
+    msg = "Path 'aa/../foo.txt' must not contain '..' component"
+    with pytest.raises(Exception, match=re.escape(msg)):
         assert_relative_path("aa/../foo.txt", "file")
 
 
+@pytest.mark.skipif(os.name != "nt", reason="Windows-specific test")
+def test_can_test_for_relative_path_windows():
+    msg = "Expected file path 'C:\\aa\\foo.txt' to be a relative path"
+    with pytest.raises(Exception, match=re.escape(msg)):
+        assert_relative_path("C:\\aa\\foo.txt", "file")
+
+    msg = "Expected file path 'C:foo.txt' to be a relative path"
+    with pytest.raises(Exception, match=re.escape(msg)):
+        assert_relative_path("C:foo.txt", "file")
+
+    msg = "Expected file path '\\aa\\foo.txt' to be a relative path"
+    with pytest.raises(Exception, match=re.escape(msg)):
+        assert_relative_path("\\aa\\foo.txt", "file")
+
+
 def test_all_normal_files_recurses(tmp_path):
     helpers.touch_files(
         tmp_path / "foo.txt",