Re: tcc 0.9.28rc testing: bug in autoconf 2.71 with AC_CHECK_DEFINE

Hi,

On 2023-09-23, Detlef Riekenberg <[email protected]> wrote:
> During testing of tcc 0.9.28rc,
> I found a strange bug in autoconf 2.71 with `AC_CHECK_DEFINE` for
> `__unix__`.

The word AC_CHECK_DEFINE is not found anywhere in the Autoconf
source code or documentation.

So I am afraid it is a bit difficult to understand this report.

[snip]
> Please test this snipped with the current 2.72rc:
> ```
> AC_CHECK_DEFINE(__unix, CFLAGS="-DFOUND__unix $CFLAGS")
> AC_CHECK_DEFINE(__unix__, CFLAGS="-DFOUND__unix__ $CFLAGS")
> AC_CHECK_DEFINE(__linux__, CFLAGS="-DFOUND__linux__ $CFLAGS")

As expected, if I translate this into an "obvious" configure.ac by
adding the mandatory AC_INIT and AC_OUTPUT expansions, I just get:

  configure.ac:3: error: possibly undefined macro: AC_CHECK_DEFINE
  [...]

So it sounds lkie there must be some third party code involved which
is defining this macro (and this code is defining macros in the AC_*
namespace to make it look like it came from Autoconf when in fact it
did not).

That doesn't mean there isn't a bug in Autoconf.  It would be helpful if
you could produce a complete self-contained test case which demonstrates
the problem, one that doesn't depend on code from outside of Autoconf
which we don't necessarily have.

Cheers,
  Nick