Surprising behavior of AM_CONDITIONAL

[Phil Edwards <phil at jaj dot com>]

A snippet of irc conversation:

  [13:44:09] <pme> Here's the question:  we have some AM_CONDITIONAL
     statements in configure, and in a Makefile.am, we have some
     corresponding "if" statements.  What happens if the AM_CONDITIONAL
     is never executed?
  [13:44:49] <DannyB> pme: Nuclear holocaust?
  [13:44:47] <pme> It /looks/ like neither the true nor false case gets a
     '#' setting in config.status, which means that /both/ statements in
     the Makefile are executed.
  [13:45:21] <pme> I say "looks"... that's the behavior I'm actually seeing,
     and my working theory is that the AM_CONDITIONAL isn't being run.
  [13:46:49] <pme> ...and it really surprises me that  a binary conditional
     defaults to "both".  :-(

So, the code in, e.g., testsuite/Makefile.am which goes

    # Enable wchar_t tests if capable.
    if GLIBCPP_TEST_WCHAR_T
    all-local: stamp_wchar
    else
    all-local:
    endif

becomes

    all-local: stamp_wchar
    all-local:

which is Extraordinarily Bad on a platform which /would/ have taken the
'false' branch, /if/ this

    AM_CONDITIONAL(GLIBCPP_TEST_WCHAR_T, test "$enable_wchar_t" = yes)

had ever been executed.

Two problems here.  One is the "you get both results" behavior of automake.
No ideas on what to do about that, if anything.  I suspect this is simply a
"don't do that".

The other problem is that, in the cross-compiling case, where we don't
specify a particular target, the generic branch isn't doing those GLIBCPP_*
calls which would eventually call AM_CONDITIONAL.  I think we might have
to pull all the AM_CONDITIONAL calls out to the bottom of configure.in,
after the Big Painful 'if' Statement.  This will entail pulling all the
variables used by the AM_CONDITIONALs out to before the BPiS, to give them
sane defaults:

    # configure.in
    enable_wchar_t=no

    if test x"$build" != x"$host"; then
        ...300+ lines...
    else
        ...native tests...
        GLIBCPP_CHECK_WCHAR_T_SUPPORT
    fi

    AM_CONDITIONAL(GLIBCPP_TEST_WCHAR_T, test "$enable_wchar_t" = yes)

Thoughts?

Phil

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