Prevent copying tmp dir to itself in build backend

Previously, setting `TMPDIR="$(pwd)/smth-inside"` would cause the
in-tree PEP 517 build backend to go into infinite recursion,
attempting to copy the project directory into a nested folder.

Specifically, this is happening in the Fedora land because macros
used in RPM packaging (`pyproject-rpm-macros`) are setting it up
like this. Additionally, this is only happening with `pip wheel` and
doesn't affect `pyproject-build`, because the latter pre-copies the
project directory by itself early, and changes current working
directory to it while the former does not.

This patch addresses the issue by excluding the temporary directory
from traversal when copying the directory tree within the build
backend.

Co-Authored-By: Miro Hrončok <miro@hroncok.cz>

packaging/pep517_backend/_backend.py

@@ -7,6 +7,7 @@
 import os
 import typing as t  # noqa: WPS111
 from contextlib import contextmanager, suppress
+from functools import partial
 from pathlib import Path
 from shutil import copytree
 from sys import version_info as _python_version_tuple
@@ -192,12 +193,44 @@ def _get_sanitized_long_description(self):  # noqa: WPS430
         _DistutilsDistributionMetadata.get_long_description = orig_func
 
 
+def _exclude_dir_path(
+    excluded_dir_path: Path,
+    visited_directory: str,
+    _visited_dir_contents: list[str],
+) -> list[str]:
+    """Prevent recursive directory traversal."""
+    # This stops the temporary directory from being copied
+    # into self recursively forever.
+    # Ref: https://github.com/aio-libs/yarl/issues/992
+    visited_directory_subdirs_to_ignore = [
+        subdir
+        for subdir in _visited_dir_contents
+        if excluded_dir_path == Path(visited_directory) / subdir
+    ]
+    if visited_directory_subdirs_to_ignore:
+        print(
+            f'Preventing `{excluded_dir_path !s}` from being '
+            'copied into itself recursively...',
+            file=_standard_error_stream,
+        )
+    return visited_directory_subdirs_to_ignore
+
+
 @contextmanager
 def _in_temporary_directory(src_dir: Path) -> t.Iterator[None]:
     with TemporaryDirectory(prefix='.tmp-ansible-pylibssh-pep517-') as tmp_dir:
+        tmp_dir_path = Path(tmp_dir)
+        root_tmp_dir_path = tmp_dir_path.parent
+        _exclude_tmpdir_parent = partial(_exclude_dir_path, root_tmp_dir_path)
+
         with chdir_cm(tmp_dir):
-            tmp_src_dir = Path(tmp_dir) / 'src'
-            copytree(src_dir, tmp_src_dir, symlinks=True)
+            tmp_src_dir = tmp_dir_path / 'src'
+            copytree(
+                src_dir,
+                tmp_src_dir,
+                ignore=_exclude_tmpdir_parent,
+                symlinks=True,
+            )
             os.chdir(tmp_src_dir)
             yield