Re: deprecated symbol warnings

[Neil Jerram <neil@ossau.uklinux.net>]

Ken Raeburn wrote:
> 
> Well, I've got a rough version up and limping, that does both 
> compile-time and link-time warnings:

This looks very useful.  I'm not an expert in this kind of thing, but 
here are some comments.

> % make depr
> gcc -I/var/raeburn/guile/guile-afs/Install/include -g   -c -o depr.o 
> depr.c
> depr.c: In function `main':
> depr.c:6: warning: `SCM_ICDR' is deprecated (declared at 
> /var/raeburn/guile/guile-afs/Install/include/libguile/deprecated.h:54)
> gcc -o depr depr.o -L/var/raeburn/guile/guile-afs/Install/lib -lguile
> depr.o(.text+0x15): In function `main':
> /var/raeburn/guile/guile-afs/test/depr.c:6: SCM_ICDR is deprecated, 
> please don't use it

Nice output.

> (No warning is printed at run time.)

Yes, that makes sense.

> The warnings can be disabled while building guile (only while building 
> deprecated.c, I hope) so that -Werror doesn't kill the build.
> 
> In the header files, here's how it's taking shape, roughly:
> 
> #if defined(SCM_DISABLE_DEPRECATION_WARNINGS)
> # define SCM_DECL_DEPRECATED /* empty */
> #elif __GNUC__ >= 3
> # define SCM_DECL_DEPRECATED __attribute__((deprecated))
> #elif defined _WIN32

Does the __declspec syntax work for all Windows compilers?  If it's 
actually specific to MSVC (which is the only compiler I'm familiar 
with), you should use _MSC_VER.  If it's for all Windows compilers, I'm 
surprised by the underscore - i.e. I'd normally use WIN32; are WIN32 and 
_WIN32 equivalent?

> /* TBD: How many old versions of the compiler support this?
>     Will older ones complain, or ignore it?  */
> # define SCM_DECL_DEPRECATED __declspec(deprecated) /* UNTESTED */
> #else
> # define SCM_DECL_DEPRECATED /* empty, no compile-time warnings */
> #endif
> 
> 
> /* N.B.: Application code will sometimes test whether one of these
>     macros is defined, to figure out if the version of Guile in use
>     predates the creation of the macro.  So at deprecation time, we
>     still want the macro to be visible.  ANSI C says "#define foo foo"
>     is okay, but if we get complaints about it, try switching the
>     non-macro name to "foo_" or "foo_deprecated" or something; make it
>     a simple concatenation so that we can make the other macros
>     continue to be simple.  */

I think we should assume in advance that we'll hit trouble with this on 
some platforms.  Otherwise it's just another hiccup to push people away 
from trying Guile out.

> 
> /* From eval.h: Macros for handling ilocs.  These were deprecated in 
> guile
>   * 1.7.0 on 2004-04-22.  */
> extern SCM_DECL_DEPRECATED scm_t_bits SCM_IFRINC;
> extern SCM_DECL_DEPRECATED scm_t_bits SCM_ICDR;
> #define SCM_IFRINC		SCM_IFRINC
> #define SCM_ICDR		SCM_ICDR
> 
> extern SCM_DECL_DEPRECATED long SCM_IFRAME(SCM n);
> #define SCM_IFRAME		SCM_IFRAME

Nice.  Slight extra overhead, but well worth it IMO for the extra function.

> The link-time warnings are a bit messier.

What is the extra benefit of link-time warnings over compile-time?  Are 
there any cases where the user will see a link-time warning without a 
corresponding compile-time one?  Would link-time warnings show up when 
linking against a 3rd party library that chose to use deprecated symbols?

> scm_c_issue_deprecation_warning (though I don't know if I need to worry 
> about i18n interactions there).

I don't believe it's yet been suggested that we would translate the 
Scheme names of primitives, so I doubt there would be a problem here. 
(Out of interest, do any other scripting languages do this?)

Regards,
	Neil


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