On 2020-08-18 I encountered a weird interaction between gl_ANSI_CXX
(used when the C++ compiler is optional) and AC_PROG_CXX (used when
the C++ compiler is mandatory). I scratched my head against it.
Zack Weinberg scratched his head against it. The difference is that
Zack found the solution :-)
2020-12-07 Bruno Haible <br...@clisp.org>
Correct interaction between gl_ANSI_CXX and AC_PROG_CXX.
Suggested by Zack Weinberg in
<https://savannah.gnu.org/support/?110294>.
* m4/ansi-c++.m4 (gl_ANSI_CXX): Mark AC_PROG_CXX as provided.
* modules/uchar-c++-tests: Revert the workaround from 2020-08-18.
diff --git a/m4/ansi-c++.m4 b/m4/ansi-c++.m4
index f93c324..1b81996 100644
--- a/m4/ansi-c++.m4
+++ b/m4/ansi-c++.m4
@@ -1,4 +1,4 @@
-# ansi-c++.m4 serial 11
+# ansi-c++.m4 serial 12
dnl Copyright (C) 2002-2003, 2005, 2010-2020 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -145,4 +145,8 @@ EOF
AC_DEFUN([gl_ANSI_CXX],
[
gl_PROG_ANSI_CXX([CXX], [ANSICXX])
+ dnl This line is needed in order to avoid trouble with Autoconf. It makes
+ dnl sure that Autoconf does not insert expansions of AC_PROG_CXX at random
+ dnl places. See <https://savannah.gnu.org/support/?110294>.
+ m4_provide([AC_PROG_CXX])
])
diff --git a/modules/uchar-c++-tests b/modules/uchar-c++-tests
index 351bdff..2cbc331 100644
--- a/modules/uchar-c++-tests
+++ b/modules/uchar-c++-tests
@@ -16,16 +16,15 @@ if test "$CXX" != no; then
dnl have the <cuchar> header file from C++11.
AC_CACHE_CHECK([whether the C++ compiler has <cuchar>],
[gl_cv_cxxheader_cuchar],
- [dnl We can't use AC_LANG_PUSH([C++]) and AC_LANG_POP([C++]) here, due to
- dnl an autoconf bug <https://savannah.gnu.org/support/?110294>.
- echo '#include <cuchar>' > conftest.cpp
- gl_command="$CXX $CXXFLAGS $CPPFLAGS -c conftest.cpp"
- if AC_TRY_EVAL([gl_command]); then
- gl_cv_cxxheader_cuchar=yes
- else
- gl_cv_cxxheader_cuchar=no
- fi
- rm -fr conftest*
+ [AC_LANG_PUSH([C++])
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <cuchar>]],
+ [[]])
+ ],
+ [gl_cv_cxxheader_cuchar=yes],
+ [gl_cv_cxxheader_cuchar=no])
+ AC_LANG_POP([C++])
])
else
gl_cv_cxxheader_cuchar=no
