gh-120754: _io Ensure stat cache is cleared on fd change (#125166)

Performed an audit of `fileio.c` and `_pyio` and made sure anytime the
fd changes the stat result, if set, is also cleared/changed.

There's one case where it's not cleared, if code would clear it in
__init__, keep the memory allocated and just do another fstat with the
existing memory.

1 files changed, 3 insertions, 0 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 7b6d10c..42b0aea 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1480,6 +1480,7 @@ class FileIO(RawIOBase):
         """
         if self._fd >= 0:
             # Have to close the existing file first.
+            self._stat_atopen = None
             try:
                 if self._closefd:
                     os.close(self._fd)
@@ -1583,6 +1584,7 @@ class FileIO(RawIOBase):
                     if e.errno != errno.ESPIPE:
                         raise
         except:
+            self._stat_atopen = None
             if owned_fd is not None:
                 os.close(owned_fd)
             raise
@@ -1756,6 +1758,7 @@ class FileIO(RawIOBase):
         called more than once without error.
         """
         if not self.closed:
+            self._stat_atopen = None
             try:
                 if self._closefd:
                     os.close(self._fd)