gh-151238: Check for _get_resized_exprs failure in _PyPegen_{joined,template}_str

[StanFromIreland]

There are several cases where _get_resized_exprs can fail and return NULL (all of which are quite rare, however):

cpython/Parser/action_helpers.c

Lines 1341 to 1344 in e2bd50d

	const char* quote_str = PyBytes_AsString(a->bytes);
	if (quote_str == NULL) {
	return NULL;
	}

cpython/Parser/action_helpers.c

Lines 1362 to 1368 in e2bd50d

	if (asdl_seq_LEN(values) != 2) {
	PyErr_Format(PyExc_SystemError,
	string_kind == TSTRING
	? "unexpected TemplateStr node without debug data in t-string at line %d"
	: "unexpected JoinedStr node without debug data in f-string at line %d",
	item->lineno);
	return NULL;

cpython/Parser/action_helpers.c

Lines 1347 to 1351 in e2bd50d

	asdl_expr_seq *seq = _Py_asdl_expr_seq_new(total_items, p->arena);
	if (seq == NULL) {
	return NULL;
	}

cpython/Parser/action_helpers.c

Lines 1401 to 1404 in e2bd50d

	resized_exprs = _Py_asdl_expr_seq_new(index, p->arena);
	if (resized_exprs == NULL) {
	return NULL;
	}

And the one triggered by the reproducer in the issue (which I test):

cpython/Parser/action_helpers.c

Lines 1383 to 1386 in e2bd50d

	item = _PyPegen_decode_fstring_part(p, is_raw, item, b);
	if (item == NULL) {
	return NULL;
	}

_PyPegen_decode_fstring_part returns NULL because it calls _PyPegen_decode_string which in turn calls warn_invalid_escape_sequence which triggers the failure as it tries to import modules to issue a warning, but gets a TypeError.

• Issue: Debug abort compiling fstring concatenation with broken imports #151238

[pablogsal]

Thanks @StanFromIreland

[miss-islington-app]

Thanks @StanFromIreland for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @StanFromIreland, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 4b44b1e1fd654f3a3fefb02ae7fb26456fe33dc3 3.13

[bedevere-app]

GH-151344 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-151345 is a backport of this pull request to the 3.14 branch.

[StanFromIreland]

This doesn’t need a backport to 3.13, this was introduced as part of the t-strings implementation. The _get_resized_exprs function is inline there:

cpython/Parser/action_helpers.c

Lines 1359 to 1368 in 1d74300

	}
	}
	else {
	resized_exprs = seq;
	}
	return _PyAST_JoinedStr(resized_exprs, a->lineno, a->col_offset,
	b->end_lineno, b->end_col_offset,
	p->arena);
	}