Reject project that have neither a pyproject.toml nor a setup.py

Before it sometimes errored out.

src/pip/_internal/pyproject.py

@@ -48,6 +48,12 @@ def load_pyproject_toml(
     has_pyproject = os.path.isfile(pyproject_toml)
     has_setup = os.path.isfile(setup_py)
 
+    if not has_pyproject and not has_setup:
+        raise InstallationError(
+            f"{req_name} does not appear to be a Python project: "
+            f"no pyproject.toml or setup.py"
+        )
+
     if has_pyproject:
         with open(pyproject_toml, encoding="utf-8") as f:
             pp_toml = tomli.load(f)

src/pip/_internal/req/constructors.py

@@ -25,7 +25,6 @@
 from pip._internal.req.req_file import ParsedRequirement
 from pip._internal.req.req_install import InstallRequirement
 from pip._internal.utils.filetypes import is_archive_file
-from pip._internal.utils.misc import is_installable_dir
 from pip._internal.utils.urls import path_to_url
 from pip._internal.vcs import is_url, vcs
 
@@ -232,12 +231,7 @@ def _get_url_from_path(path: str, name: str) -> Optional[str]:
     an @, it will treat it as a PEP 440 URL requirement and return the path.
     """
     if _looks_like_path(name) and os.path.isdir(path):
-        if is_installable_dir(path):
-            return path_to_url(path)
-        raise InstallationError(
-            f"Directory {name!r} is not installable. Neither 'setup.py' "
-            "nor 'pyproject.toml' found."
-        )
+        return path_to_url(path)
     if not is_archive_file(path):
         return None
     if os.path.isfile(path):