`window.insnstr()` leaks its `bytes` argument when setting `attr` fails

[fedonman]

Bug description:

window.insnstr(str, n, attr) sets the window rendition before the write, and when that fails it never releases the bytes object it converted its argument to, so every failing call leaks one reference. addstr(), addnstr() and insstr() got that release in GH-145609 (gh-145376); insnstr() was missed.

A window detached by screen.close() makes the rendition call fail:

import curses, sys

screen = curses.newterm()
win = screen.stdscr
screen.close()
data = b'x' * 40
before = sys.getrefcount(data)
for _ in range(100):
    try:
        win.insnstr(data, 8, curses.A_BOLD)
    except curses.error:
        pass
print('insnstr leaked', sys.getrefcount(data) - before, 'references', file=sys.stderr)

insnstr leaked 100 references

Expected: insnstr leaked 0 references.

Only main is affected: 3.15 has the same omission, but nothing there detaches a window, so the rendition call cannot fail.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-156953: Fix a reference leak in curses window.insnstr() #156954