Re: C++ libtool build error?

[Bruno Haible]

Eric Blake wrote:
> Which begs the question - why is gnulib-tool making C-only projects to
> import C++ test files?  It seems like C++ files should be excluded
> unless the developer explicitly requests that both C and C++ be supported.

Simon Josefsson wrote:
> > So, the fix is to add an LT_LANG([CXX]) invocation to your configure.ac.
> > This fixes it for libunistring.
> 
> That doesn't make a lot of sense to me because
> 
>    1) It violates the modularity of gnulib.  Gnulib is adding the C++
>       code to my project, so I believe gnulib should be responsible for
>       making sure the files build.
> 
>    2) LT_LANG([CXX]) doesn't exist in libtool 1.5.x which is still
>       supported by gnulib.
> 
> The fix you applied is just for --create-testdir (right?) so that patch
> by itself doesn't modify anything for libidn or libunistring as far as I
> can tell.
> ...
> Alternatively, some solution that detected that C++ code isn't relevant
> for the particular project, and didn't try to build those files.

Actually, there are quite a number of tests that not every project may
want to carry in its testsuite, but that should be packageable via
--create-testdir:
  - The C++ tests of the modules 'string', 'stdlib', etc.
  - The tests that ask for the superuser password ('idpriv-drop',
    'idpriv-droptemp').
  - The long-running tests of the 'havelib' module (currently still in
    gettext).

The solution I would propose is to put them into a module '*-extratests'.
It is like '*-tests', except that it is not included by default in
--with-tests.


Additionally, the user who installs a package might want to disable the C++
part even if it is packaged as part of the tarball. I'm applying this.

2010-03-13  Bruno Haible  <address@hidden>

        Allow the user to disable C++ code and tests.
        * m4/ansi-c++.m4 (gl_CXX_CHOICE): New macro.
        (gl_PROG_ANSI_CXX): Require it.

--- m4/ansi-c++.m4.orig Sat Mar 13 17:30:01 2010
+++ m4/ansi-c++.m4      Sat Mar 13 17:28:22 2010
@@ -1,11 +1,26 @@
-# ansi-c++.m4 serial 2
-dnl Copyright (C) 2002-2003, 2010 Free Software Foundation, Inc.
+# ansi-c++.m4 serial 3
+dnl Copyright (C) 2002-2003, 2005, 2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
 dnl From Bruno Haible.
 
+# Sets CXX_CHOICE to 'yes' or 'no', depending on the preferred use of C++.
+
+AC_DEFUN([gl_CXX_CHOICE],
+[
+  AC_MSG_CHECKING([whether to use C++])
+  dnl It would be so nice if plus signs were supported in AC_ARG_ENABLE.
+  dnl Feature request submitted on 2010-03-13.
+  AC_ARG_ENABLE([cxx],
+    [  --disable-cxx           do not build C++ sources],
+    [CXX_CHOICE="$enableval"],
+    [CXX_CHOICE=yes])
+  AC_MSG_RESULT([$CXX_CHOICE])
+  AC_SUBST([CXX_CHOICE])
+])
+
 # gl_PROG_ANSI_CXX([ANSICXX_VARIABLE], [ANSICXX_CONDITIONAL])
 # Sets ANSICXX_VARIABLE to the name of a sufficiently ANSI C++ compliant
 # compiler, or to ":" if none is found.
@@ -14,8 +29,12 @@
 
 AC_DEFUN([gl_PROG_ANSI_CXX],
 [
+  AC_REQUIRE([gl_CXX_CHOICE])
   m4_if([$1], [CXX], [],
     [gl_save_CXX="$CXX"])
+  if test "$CXX_CHOICE" = no; then
+    CXX=":"
+  fi
   if test -z "$CXX"; then
     if test -n "$CCC"; then
       CXX="$CCC"