Re: new module 'noreturn'

[Bruno Haible]

Hi Paul,

> I thought we had established that in some cases one should apply both 
> _Noreturn and __attribute__ ((__noreturn__)) to the same declaration? I 
> don't see that in this module.

Apparently we've been thinking at different solutions of the clang problem
(which, for type checking / assignment purposes, considers _Noreturn to
be different from __attribute__((__noreturn__))).

My solution in the proposed noreturn.h is to
  #define _GL_NORETURN_FUNC    __attribute__ ((__noreturn__))
  #define _GL_NORETURN_FUNCPTR __attribute__ ((__noreturn__))
in this case. So clang won't warn.

You have been thinking of this?
  #define _GL_NORETURN_FUNC    _Noreturn
  #define _GL_NORETURN_FUNCPTR _Noreturn __attribute__ ((__noreturn__))

> Also, I hope we're not envisioning a lot of replacement of _Noreturn 
> with _GL_NORETURN_FUNC in other modules.

No, most of these functions (dfaerror, openat_save_fail, _Exit, xalloc_die, ...)
are not likely to be stored in function pointers.

> As I understand it, 
> _GL_NORETURN_FUNC is needed only for functions that one wants to take 
> addresses of, and to store these addresses in _GL_NORETURN_FUNCPTR 
> variables. Most existing modules don't need to do this, and so can 
> continue to use _Noreturn. This point should be made in the comments.

Good point. And for C++ support (other than g++ and MSVC) as well. I'm squashing
in this comment change:

--- a/lib/noreturn.h
+++ b/lib/noreturn.h
@@ -29,6 +29,16 @@
    _GL_NORETURN_FUNC is for use in function declarations and function
    definitions.
    _GL_NORETURN_FUNCPTR is for use on function pointers.
+
+   Comparison of this file with <stdnoreturn.h>:
+   <stdnoreturn.h> defines a macro (or keyword) _Noreturn that declares
+   a function to be non-returning.  _Noreturn is only for use in function
+   declarations and function definitions.
+   Therefore, if the non-returning functions you have to declare are unlikely
+   to be accessed through function pointers, and if the efficiency with C++
+   compilers other than g++, clang, MSVC++ is not an issue to you, you can use
+   module 'stdnoreturn' instead of this one, and _Noreturn instead of
+   _GL_NORETURN_FUNC.
  */
 
 /* Declares that a function is nonreturning.