Unused argument variable in header file

[correaa]

• I believe this to be a bug with Open Babel
• This is a feature request

Environment Information

Open Babel version: 3.1
Operating system and version: Ubuntu 20.04

Expected Behavior

Code using reasonable warning level should not warn on header code

Actual Behavior

Code including directly or indirectly openbabel/base.h warns about unused

Steps to Reproduce

Compile any example code with -Wall -Wextra (or anything including -Wunused-parameters).

Proposed fix

I think there is a detail in the definition of the macro UNUSED in the same file.

#ifdef UNUSED
#elif (__GNUC__ == 4)
# define UNUSED(x) UNUSED_ ## x __attribute__((unused))
#elif defined(__LCLINT__)
# define UNUSED(x) /*@unused@*/ x
#else
# define UNUSED(x) x  // <<<<<<<<<<<<<<<< PROBLEM HERE
#endif

The fallback case should be to define UNUSED(x) as empty

# define UNUSED(x)

or

# define UNUSED(x) /**/

[e-kwsm]

In #2075 I use [[maybe_unused]] attribute if available.

[correaa]

I think this change makes a lot of sense: fb7d831