Re: [PATCH] build: avoid link failure on systems using gnulib's fcntl but not open

[Bruno Haible]

Jim Meyering wrote:
> I noticed this build failure for grep:
> 
>     http://hydra.nixos.org/build/329919
> 
>       CCLD   grep
>     Undefined symbols:
>       "_rpl_open", referenced from:
>           _grepfile in grep.o
>     ld: symbol(s) not found
>     collect2: ld returned 1 exit status
>     make[2]: *** [grep] Error 1
> 
> I fixed it with this change to grep, and do appreciate
> the implied warning that grep needs the "open" module,
> but this must be a bug in gnulib...
> ...
> * bootstrap.conf (gnulib_modules): Using gnulib's fcntl module
> and including <fcntl.h>, but not also using gnulib's "open" module
> would result in link failure due to references to rpl_open
> on systems requiring the replacement (e.g., Cygwin and Darwin).

I wouldn't say that it's a bug in gnulib. The situation in the 'grep'
package is as follows:
  - The main part, in lib/, has the module 'fcntl' and therefore
    implicitly 'fcntl-h', but not the 'open' module.
  - The tests part, in gnulib-tests/, has the module 'open', as a
    dependency from 'dup2-tests'.
  - The presence of the 'open' module is indicated through an
    AC_SUBSTed variable GNULIB_OPEN. There is only one GNULIB_OPEN
    for the entire package, and it is set to 1.
  - Therefore the lib/fcntl.h replacement defines "#define open rpl_open".

It's a limitation of gnulib that you cannot decide to not use a module in
the main part but use it in the tests. If you really wanted that, you
would need a setup with two different configure.ac files, one for the
main part and one for the tests.

Bruno