Re: conditionally include gnulib regex

[Bruno Haible]

Hi,

> The strategy is to hide
> lib/regex.h until configure requests it.  If there’s a better
> way, I’d be interested to know and apologize if this
> has been covered previously.

Technically, the way you use regex here is OK.

Nevertheless, here is why few package have an option like this:
The user of 'configure', i.e. the person who builds the package, usually
for a distro, when seeing this

   $ ./configure --help
   ...
   --with-included-regex       use GNU gnulib regex library included here
   ...

will ask themselves: Should I use this option or not? What is the benefit
(added feature?) if I use it?

Many GNU packages therefore offer to the user of 'configure' a set of
features, with a clear meaning, and the configure script then makes decisions
(in this case, whether to include the system's <regex.h>). For example:

   $ ./configure --help
   ...
   --enable-posix              enable strict POSIX compliance
   --enable-gnu                enable GNU extensions
   --enable-embedded           produce binaries of minimal code size
   ...

Then, you can implement a logic such as:
  included_regex = (enable_posix && !system_has_posix_regex)
                   || (enable_gnu && !system_has_gnu_regex)
                   || (!enable_embedded && system_regex_is_buggy)

This is just a hypothetical example.

> AM_CPPFLAGS += -DRE_ENABLE_I18N=1 -D__USE_GNU=1

You shouldn't set __USE_GNU. That's a glibc-internal macro. If you want
GNU extensions to be defined in glibc, define _GNU_SOURCE to 1 before
the first include file. If you want platform specific functions to be
declared on all platforms, use the gnulib module 'extensions'.

Bruno