Guillaume Le Vaillant writes:

> Zhu Zihao <all_but_last@163.com> skribis:
>
>> ECL's header includes the header of gmp, libgc, libatomic-ops and
>> libffi. This help fix some program use ecl as build input failed to link
>> with it.
>
> I tried a `guix environment -C --ad-hoc ecl -- ecl --eval '(compile-file "test.lisp")'`
> and ECL compiled the file successfully, so it must have found the
> headers it needed.

Because we already wrapped ECL executable with CPATH and LIBRARY_PATH
environment variable. so any compilation done in ECL can find the
library and header.

If some 3-rd party program want to link with ECL(If they use ECL as
thier extension language). Compiler will failed to find gmp, libgc etc.

A simple example here, start with `guix environment --ad-hoc ecl`

```
chino@asus-laptop:~/tmp$ cat test.c
#include <ecl/ecl.h>

int main() {
  cl_boot(0, NULL);
  return 0;
}
chino@asus-laptop:~/tmp$ CFLAGS="$(ecl-config --cflags) $(ecl-config --ldflags) $(ecl-config --libs)"
chino@asus-laptop:~/tmp$ LANG=en_US.utf-8 gcc -c test.c -o test $CFLAGS
In file included from /gnu/store/lzfxjn036h3kis13lcc222rpwcnqazkr-ecl-20.4.24/include/ecl/ecl.h:37,
                 from test.c:1:
/gnu/store/lzfxjn036h3kis13lcc222rpwcnqazkr-ecl-20.4.24/include/ecl/config.h:59:10: fatal error: gmp.h: No such file or directory
   59 | #include "gmp.h"
      |          ^~~~~~~
compilation terminated.
```

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Zihao