Cache Path.is_dir calls (#779)

src/poetry/core/packages/dependency.py

@@ -330,6 +330,7 @@ def create_from_pep_508(
         """
         from poetry.core.packages.url_dependency import URLDependency
         from poetry.core.packages.utils.link import Link
+        from poetry.core.packages.utils.utils import cached_is_dir
         from poetry.core.packages.utils.utils import is_archive_file
         from poetry.core.packages.utils.utils import is_python_project
         from poetry.core.packages.utils.utils import is_url
@@ -361,7 +362,7 @@ def create_from_pep_508(
         else:
             path_str = os.path.normpath(os.path.abspath(name))  # noqa: PTH100
             p, extras = strip_extras(path_str)
-            if p.is_dir() and (os.path.sep in name or name.startswith(".")):
+            if cached_is_dir(p) and (os.path.sep in name or name.startswith(".")):
                 if not is_python_project(Path(name)):
                     raise ValueError(
                         f"Directory {name!r} is not installable. Not a Python project."

src/poetry/core/packages/utils/utils.py

@@ -117,10 +117,16 @@ def strip_extras(path: str) -> tuple[Path, str | None]:
     return Path(path_no_extras), extras
 
 
+@functools.lru_cache(maxsize=None)
+def cached_is_dir(path: Path) -> bool:
+    """A cached version of `Path.is_dir`."""
+    return path.is_dir()
+
+
 @functools.lru_cache(maxsize=None)
 def is_python_project(path: Path) -> bool:
     """Return true if the directory is a Python project"""
-    if not path.is_dir():
+    if not cached_is_dir(path):
         return False
 
     setup_py = path / "setup.py"