readline error when saving interactive command history when history file path is a symlink to a relative path

Bug report

Bug description:

To reproduce the issue

1. Set up home directory like following:

$HOME/
  .python_history --> foo/history_file
  foo/
    history_file

2. Launch a Python interactive session with CWD different from $HOME
3. Execute the following

import readline
import os
history_path=os.path.expanduser("~/.python_history")
assert os.path.exists(history_path)
readline.write_history_file(history_path)

4. Observe the following error

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory

Possible cause

This is likely due to how GNU readline commits history information to file. As of GNU readline v8.2 (used in Python 3.10 and 3.12 among others), it creates a temporary file in the parent directory of the history file, write to that temporary file, and then rename the temporary file to the history file. See history_tempfile in histfile.c of GNU readline.

GNU readline determines the parent directory from the readlink output of the user-supplied history file path. In this case, since the history file is a symlink with a relative path, the parent directory is resolved to the relative path foo/. If foo/ doesn't exist in the CWD, history saving fails.

CPython versions tested on:

3.10, 3.12

Operating systems tested on:

Linux

相対ターゲットのシンボリックリンクと、$HOME とは異なる作業ディレクトリを使って再現するところから始めます。histfile.c にある GNU readline の history_tempfile のロジックを読み、CPython's readline.write_history_file がどのようにそこへ到達するかを追跡します。テストした Linux 構成で、説明したシンボリックリンク構成に対する履歴の保存が成功し、このケースのリグレッションカバレッジが追加されていれば完了です。