Re: [PATCH] bug fixes for AS_IF and _AC_LANG_COMPILER_GNU

[Paul Eggert]

On 3/14/20 7:31 AM, Jannick wrote:

> - AS_IF: cope with blank false branch.
> - _AC_LANG_COMPILER_GNU: make cached result available to calling macro.

Thanks, I installed the _AC_LANG_COMPILER_GNU patch into the master branch on 
savannah. However, the AS_IF patch causes 'make check' to fail, because 
tests/compile.at's AC_RUN_IFELSE test does this:

AC_RUN_IFELSE([AC_LANG_PROGRAM([], [return 2])],
              [AC_MSG_ERROR([saw `return 2' as a success])],
              [estatus=$?
test $estatus != 2 &&
  AC_MSG_ERROR([did not get as 2 exit status: $estatus])])

and because the AS_IF patch inserts ":" between the "else" and the "estatus=$?", 
the ":" sets $? to 0 and makes the test fail. So I did not install that patch.

Autoconf's nblank macros don't test whether the argument eventually expands to 
just blanks; it tests whether the argument currently consists of just blanks. So 
I think we'll just have to advise people to write [] instead of [[]] when they 
want the empty string. The Autoconf manual already contains a couple of examples 
illustrating why [] and [[]] are not the same thing, so I added one more example 
by installing the attached documentation patch.

0001-Document-AS_IF-.-.-glitch.patch
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