readline leaks the completer delimiters buffer on re-import #160353

Bug report

Re-importing readline after removing it from sys.modules leaks the buffer allocated by set_completer_delims().

Reproduced on Linux with an AddressSanitizer build of CPython main, commit ad101c3 (3.16.0a1+dev):

  ASAN_OPTIONS=detect_leaks=1 ./python -I -S -B -c 'import readline, sys; readline.set_completer_delims("x" * 28); del sys.modules["readline"]; import readline'

LeakSanitizer reports 29 bytes leaked in one allocation, originating from strdup() in readline_set_completer_delims_impl() (Modules/readline.c:853).

During re-import, setup_readline() overwrites completer_word_break_characters with a new allocation without freeing the previous buffer. Repeated calls to set_completer_delims() without re-importing do not
reproduce the leak.

Related reports: #94064, #152398.

CPython versions tested on:

CPython main branch, 3.16, 3.15

Operating systems tested on:

Linux

Linked PRs

• gh-160353: Fix readline memory leak on re-import #160379