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Re: deprecated symbol warnings

From: Neil Jerram
Subject: Re: deprecated symbol warnings
Date: Sat, 14 May 2005 13:40:42 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.7) Gecko/20050420 Debian/1.7.7-2

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:

# 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 */
# define SCM_DECL_DEPRECATED /* empty, no compile-time warnings */

/* 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.  */
#define SCM_IFRINC              SCM_IFRINC
#define SCM_ICDR                SCM_ICDR

#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?)


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