get_vcs: improve Cygwin git support under Windows

src/poetry/core/vcs/__init__.py

@@ -1,17 +1,18 @@
 from __future__ import annotations
 
-import os
 import subprocess
 
-from pathlib import Path
+from typing import TYPE_CHECKING
 
 from poetry.core.vcs.git import Git
 
 
-def get_vcs(directory: Path) -> Git | None:
-    working_dir = Path.cwd()
-    os.chdir(str(directory.resolve()))
+if TYPE_CHECKING:
+    from pathlib import Path
+
 
+def get_vcs(directory: Path) -> Git | None:
+    directory = directory.resolve(strict=True)
     vcs: Git | None
 
     try:
@@ -21,23 +22,23 @@ def get_vcs(directory: Path) -> Git | None:
             [executable(), "check-ignore", "."],
             stderr=subprocess.DEVNULL,
             stdout=subprocess.DEVNULL,
+            cwd=directory,
         ).returncode
 
         if check_ignore == 0:
             vcs = None
         else:
-            git_dir = subprocess.check_output(
-                [executable(), "rev-parse", "--show-toplevel"],
+            rel_path_to_git_dir = subprocess.check_output(
+                [executable(), "rev-parse", "--show-cdup"],
                 stderr=subprocess.STDOUT,
                 text=True,
                 encoding="utf-8",
+                cwd=directory,
             ).strip()
 
-            vcs = Git(Path(git_dir))
+            vcs = Git((directory / rel_path_to_git_dir).resolve())
 
     except (subprocess.CalledProcessError, OSError, RuntimeError):
         vcs = None
-    finally:
-        os.chdir(str(working_dir))
 
     return vcs

tests/vcs/test_vcs.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import os
 import subprocess
 
 from pathlib import Path
@@ -480,3 +481,47 @@ def test_get_vcs_encoding(tmp_path: Path) -> None:
     assert vcs is not None
     assert vcs._work_dir is not None
     assert vcs._work_dir.exists()
+    assert vcs._work_dir == repo_path
+
+
+def test_get_vc_subdir(tmp_path: Path) -> None:
+    repo_path = tmp_path / "répö"
+    repo_path.mkdir()
+    assert repo_path.exists()
+    assert subprocess.check_call([executable(), "init"], cwd=repo_path) == 0
+    subdir = repo_path / "subdir"
+    subdir.mkdir()
+    vcs = get_vcs(subdir)
+    assert vcs is not None
+    assert vcs._work_dir is not None
+    assert vcs._work_dir.exists()
+    assert vcs._work_dir == repo_path
+
+
+def test_get_vcs_no_repo(tmp_path: Path, mocker: MockerFixture) -> None:
+    repo_path = tmp_path / "répö"
+    repo_path.mkdir()
+    assert repo_path.exists()
+    assert subprocess.check_call([executable(), "init"], cwd=repo_path) == 0
+
+    # This makes sure git fails to find the git directory even if one
+    # exists at some higher level in the filesystem
+    mocker.patch.dict(os.environ, {"GIT_DIR": os.devnull})
+
+    vcs = get_vcs(repo_path)
+    assert vcs is None
+
+
+def test_get_vcs_ignored_subdir(tmp_path: Path) -> None:
+    # See https://github.com/python-poetry/poetry-core/pull/611
+    repo_path = tmp_path / "répö"
+    repo_path.mkdir()
+    assert repo_path.exists()
+    assert subprocess.check_call([executable(), "init"], cwd=repo_path) == 0
+    with open(repo_path / ".gitignore", "w", encoding="utf-8") as f:
+        f.write("/ignored")
+    subdir = repo_path / "ignored"
+    subdir.mkdir()
+
+    vcs = get_vcs(subdir)
+    assert vcs is None