`--without-tail-call-interp` actually enables the tail-call interpreter, instead of disabling!

[nelhage]

In configure.ac, if the user passes --tail-call-interp in the negative, we set Py_TAIL_CALL_INTERP to 0:

cpython/configure.ac

Lines 7027 to 7032 in 1feaecc

	if test "$withval" = no
	then
	AC_DEFINE([Py_TAIL_CALL_INTERP], [0],
	[Define if you want to use tail-calling interpreters in CPython.])
	AC_MSG_RESULT([no])
	fi

However, in ceval_macros.h and bytecodes.c, we check for #ifdef Py_TAIL_CALL_INTERP and #if defined(Py_TAIL_CALL_INTERP), for instance:

cpython/Python/ceval_macros.h

Line 76 in 1feaecc

#ifdef Py_TAIL_CALL_INTERP

)

Thus, defining the macro -- even with a value of 0 -- actually enables the feature! I think the consistent behavior (consistent with USE_COMPUTED_GOTOS) is probably to switch the preprocessor guards to #if, instead of #ifdef.

Linked PRs

• gh-129989: Properly disable tailcall interp in configure #129991
• gh-129989: Change Py_TAIL_CALL_INTERP ifndef to ! #130269

[Fidget-Spinner]

Great catch! Will fix this.

[Fidget-Spinner]

Should be fixed. Please do let us know if there are any further issues.